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The hypocretin (Hcrt) system modulates arousal and anxiety-related behaviors and has been considered as a novel treatment target for stress-related affective disorders. We examined the effects of Hcrt acting in the nucleus accumbens shell (NAcSh) and anterodorsal bed nucleus of the stria terminalis (adBNST) on social behavior in male and female California mice (Peromyscus californicus). In female but not male California mice, infusion of Hcrt1 into NAcSh decreased social approach. Weak effects of Hcrt1 on social vigilance were observed in both females and males. No behavioral effects of Hcrt1 infused into the adBNST were observed. Analyses of sequencing data from California mice and Mus musculus NAc showed that Hcrtr2 was more abundant than Hcrtr1, so we infused the selective Hcrt receptor 2 antagonist into the NAcSh, which increased social approach in females previously exposed to social defeat. A calcium imaging study in the NAcSh of females before and after stress exposure showed that neural activity increased immediately following the expression of social avoidance but not during freezing behavior. This observation is consistent with previous studies that identified populations of neurons in the NAc that drive avoidance. Intriguingly, calcium transients were not affected by stress. These data suggest that hypocretin acting in the NAcSh plays a key role in modulating stress-induced social avoidance.

Oxytocin is a versatile neuropeptide that modulates many different forms of social behavior. Recent hypotheses pose that oxytocin enhances the salience of rewarding and aversive social experiences, and the field has been working to identify mechanisms that allow oxytocin to have diverse effects on behavior. Here we review studies conducted on the California mouse (Peromyscus californicus) that shed light on how oxytocin modulates social behavior following stressful experiences. In this species, both males and females exhibit high levels of aggression, which has facilitated the study of how social stress impacts both sexes. We review findings of short- and long-term effects of social stress on the reactivity of oxytocin neurons. We also consider the results of pharmacological studies which show that oxytocin receptors in the bed nucleus of the stria terminalis and nucleus accumbens have distinct but overlapping effects on social approach behaviors. These findings help explain how social stress can have different behavioral effects in males and females, and how oxytocin can have such divergent effects on behavior. Finally, we consider how new technological developments and innovative research programs take advantage of the unique social organization of California mice to address questions that can be difficult to study in conventional rodent model species. These new methods and questions have opened new avenues for studying the neurobiology of social behavior.

A key question in biology concerns the extent to which distributional range limits of species are determined by intrinsic limits of physiological tolerance. Here, we use common‐garden data for wild rodents to assess whether species with higher elevational range limits typically have higher thermogenic capacities in comparison to closely related lowland species. Among South American leaf‐eared mice (genus Phyllotis), mean thermogenic performance is higher in species with higher elevational range limits, but there is little among‐species variation in the magnitude of plasticity in this trait. In the North American rodent genus Peromyscus, highland deer mice (Peromyscus maniculatus) have greater thermogenic maximal oxygen uptake (V̇O2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$) than lowland white‐footed mice (Peromyscus leucopus) at a level of hypoxia that matches the upper elevational range limit of the former species. In highland deer mice, the enhanced thermogenic V̇O2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ in hypoxia is attributable to a combination of evolved and plastic changes in physiological pathways that govern the transport and utilization of O2 and metabolic substrates. Experiments with Peromyscus mice also demonstrate that exposure to hypoxia during different stages of development elicits plastic changes in cardiorespiratory traits that improve thermogenic V̇O2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ via distinct physiological mechanisms. Evolved differences in thermogenic capacity provide clues about why some species are able to persist in higher‐elevation habitats that lie slightly beyond the tolerable limits of other species. Such differences in environmental tolerance also suggest why some species might be more vulnerable to climate change than others. [ABSTRACT FROM AUTHOR]

Simple Summary: Mercury is one of the most common pollutants in agricultural and industrial areas; therefore, its study has become increasingly important. This element is often quantified using biomonitors, whose gradual response is representative of the entire community. This is especially important in areas where pollution is known or suspected, like the Mezquital Valley in central Mexico. Here, we aimed to determine the total mercury concentration in three species of small wild mammals that differ in diet to identify possible exposure threats in their habitat. We took hair and liver samples from two bat species and one wild mouse species over the course of a year. We found no difference in mercury concentration among species, but liver mercury was significantly lower during the dry season. This supports previous studies that pointed to wastewater as the main source of mercury exposure in this location. This is the first study to use small wild mammals as biomonitors in the Mezquital Valley, which is a critically contaminated site, as well as the first record of toxic metals in the protected bat species Leptonycteris yerbabuenae. Mercury (Hg) has been extensively studied due to its impact on the environment and health, but its effects on wild mammal populations are still poorly known. Therefore, the use of biomonitors has gained importance. Our objective was to report and compare, for the first time, the amount of mercury in small mammals belonging to three trophic guilds and to provide an initial toxicology perspective in the Mezquital Valley, a critically polluted area of Central Mexico. We quantified total Hg from the hair and liver of a nectarivorous bat (Leptonycteris yerbabuenae), an insectivorous bat (Corynorhinus townsendii) and a granivorous mouse (Peromyscus melanophrys) using atomic absorption spectrometry during the dry and rainy seasons. We compared the mercury concentrations between seasons, species and matrices. In all species, the average mercury content was higher in hair than liver, and there was no correlation between matrices. There was no difference in mercury content among species. Hg concentrations in the livers of P. melanophrys and C. townsendii were lower during the dry season than the rainy season, suggesting a seasonal decline in mercury availability. All of the values detected were below the neurotoxicity threshold reported in small mammals (10 ppm); however, we propose constant monitoring of Hg in their environment and confirm the utility of these species as biomonitors. [ABSTRACT FROM AUTHOR]

Abstract The harsh and dry conditions of desert environments have resulted in genomic adaptations, allowing for desert organisms to withstand prolonged drought, extreme temperatures, and limited food resources. Here, we present a comprehensive exploration of gene expression across five tissues (kidney, liver, lung, gastrointestinal tract, and hypothalamus) and 19 phenotypic measurements to explore the whole-organism physiological and genomic response to water deprivation in the desert-adapted cactus mouse (Peromyscus eremicus). The findings encompass the identification of differentially expressed genes and correlative analysis between phenotypes and gene expression patterns across multiple tissues. Specifically, we found robust activation of the vasopressin renin-angiotensin-aldosterone system (RAAS) pathways, whose primary function is to manage water and solute balance. Animals reduced food intake during water deprivation, and upregulation of PCK1 highlights the adaptive response to reduced oral intake via its actions aimed at maintained serum glucose levels. Even with such responses to maintain water balance, hemoconcentration still occurred, prompting a protective downregulation of genes responsible for the production of clotting factors while simultaneously enhancing angiogenesis which is thought to maintain tissue perfusion. In this study, we elucidate the complex mechanisms involved in water balance in the desert-adapted cactus mouse, P. eremicus. By prioritizing a comprehensive analysis of whole-organism physiology and multi-tissue gene expression in a simulated desert environment, we describe the complex response of regulatory processes.

The harsh and dry conditions of desert environments have resulted in genomic adaptations, allowing for desert organisms to withstand prolonged drought, extreme temperatures, and limited food resources. Here, we present a comprehensive exploration of gene expression across five tissues (kidney, liver, lung, gastrointestinal tract, and hypothalamus) and 19 phenotypic measurements to explore the whole-organism physiological and genomic response to water deprivation in the desert-adapted cactus mouse (Peromyscus eremicus). The findings encompass the identification of differentially expressed genes and correlative analysis between phenotypes and gene expression patterns across multiple tissues. Specifically, we found robust activation of the vasopressin renin-angiotensin-aldosterone system (RAAS) pathways, whose primary function is to manage water and solute balance. Animals reduced food intake during water deprivation, and upregulation of PCK1 highlights the adaptive response to reduced oral intake via its actions aimed at maintained serum glucose levels. Even with such responses to maintain water balance, hemoconcentration still occurred, prompting a protective downregulation of genes responsible for the production of clotting factors while simultaneously enhancing angiogenesis which is thought to maintain tissue perfusion. In this study, we elucidate the complex mechanisms involved in water balance in the desert-adapted cactus mouse, P. eremicus. By prioritizing a comprehensive analysis of whole-organism physiology and multi-tissue gene expression in a simulated desert environment, we describe the complex response of regulatory processes. [ABSTRACT FROM AUTHOR]

Current grassland restoration strategies aim to recreate grassland vegetation communities, and often rely on high‐diversity native seeding to promote vegetation diversity. Questions remain concerning the influence of vegetation richness and diversity on grassland fauna. Small‐mammal communities are integral parts of grassland ecosystems, but their responses to restoration are often mixed or overlooked. During July 2014 to 2016, we used Sherman live traps to survey grassland small‐mammal communities of 24 study sites in northeastern South Dakota and southeastern North Dakota, USA, to better understand their responses to vegetation cover type, diversity, richness, and site‐specific vegetation structure. Sites represented a vegetation species richness gradient and 3 vegetation cover types including low‐diversity restorations planted with dense nesting cover (DNC) seed mix, high‐diversity seeded restorations, and unseeded reference grasslands. Small‐mammal abundance was highest at low‐diversity DNC restoration sites and lowest in reference grassland. Small‐mammal diversity was highest at high‐diversity restoration sites and lowest at low‐diversity DNC restoration sites. Models assessing the influence of vegetation structure on the abundance of focal taxa differed. Deer mice (Peromyscus spp.) were negatively influenced by percent native vegetation cover, and voles (Microtus spp.) showed yearly variation and were influenced positively by litter depth and negatively by vegetation richness. Small‐mammal communities of low‐diversity DNC restorations differed from reference sites, but high‐diversity restorations were not different from reference or low‐diversity DNC sites. Thirteen‐lined ground squirrel (Ictidomys tridecemlineatus) abundance was higher at reference and high‐diversity restored sites, while low‐diversity DNC sites had higher deer mice abundance. Results indicate small mammals are unlikely to respond uniformly to vegetation characteristics, and diversity of seed mixes used in grassland restoration is likely to influence grassland small‐mammal communities. [ABSTRACT FROM AUTHOR]

Endangered species recovery requires knowledge of species abundance, distribution, habitat preferences, and threats. Endangered beach mouse populations (Peromyscus polionotus subspp.) occur on barrier islands in Florida and Alabama. Camera traps may supplement current methods and strengthen inferences of animal activity. Between November 2020-February 2022, we conducted 140 camera surveys across 86 track tubes on Tyndall Air Force Base, Florida. We used generalized linear models to explore the relationships between beach mouse detections and environmental factors. We detected beach mice on 6,397 occasions across all tubes. Detections ranged from 0 to 147 observations/survey. Our top model suggested that beach mouse detection was related to cover type with positive associations with grassland and dune compared to scrub. Detections further varied depending on islands, were negatively associated with predator detections, and increased in winter months. Our results suggest that cameras can supplement inference about vegetation associations at broader scales to complement monthly track tube surveys since detection counts are more informative than presence/absence data alone. Given that all tubes exhibited at least one observation, the camera trap network may provide a less frequent and more robust survey method relative to monthly track tube surveys. Adopting such a multifaceted approach may reduce effort and strengthen inference to inform recovery objectives and adaptive management range-wide for all listed beach mouse subspecies. [ABSTRACT FROM AUTHOR]

Lyme disease has expanded into the Great Plains of the USA. To investigate local enzootic transmission, small mammals were trapped in two forested tracts in northeastern North Dakota during 2012 and 2013. Peromyscus mice and southern red-backed voles, Myodes gapperi, comprised over 90% of all mammals captured. One site was dominated by Peromyscus (79% of 100 mammals captured). At the other site, M. gapperi (59% of 107 mammals captured) was more abundant than Peromyscus (36%). Immature stages of two tick species parasitized small mammals: Dermacentor variabilis and Ixodes scapularis. Larval I. scapularis ectoparasitism was significantly higher on Peromyscus (81% infested; 3.7 larvae per infested mouse) than M. gapperi (47% infested; 2.6 larvae per infested vole) whereas larval and nymphal D. variabilis ectoparasitism were highest on M. gapperi. Over 45% of infested rodents were concurrently infested with both tick species. Testing engorged I. scapularis larvae from Peromyscus (n = 66) and M. gapperi (n = 20) yielded xenopositivity prevalence for Borrelia burgdorferi sensu lato (s.l.) in these rodents of 6% and 5%, respectively. Progeny of field collected M. gapperi were used to determine host infectivity for a local isolate of B. burgdorferi sensu stricto (s.s.). Five M. gapperi were injected with spirochetes, infested with pathogen-free I. scapularis larvae on days 10, 20, and 40 after infection, and engorged larvae molted to nymphs. Subsamples of nymphs were tested by PCR for B. burgdorferi s. s. DNA and yielded infection rates of 56% (n = 100 nymphs tested), 75% (n = 8) and 64% (n = 31), respectively. The remaining infected nymphs were fed on BALB/c Mus musculus mice and 7 d later, mice were euthanized, and tissues were cultured for B. burgdorferi s.s. Nymphs successfully transmitted spirochetes to 13 of 18 (72%) mice that were exposed to 1–5 infected ticks. Theoretical reservoir potentials – i.e., ability to generate B. burgdorferi infected nymphs – were compared between Peromyscus and M. gapperi. At one site, Peromyscus accounted for nearly all Borrelia-infected nymphs produced (reservoir potential value of 0.935). At the other site, the reservoir potentials for Peromyscus (0.566) and M. gapperi (0.434) were comparable. The difference was attributed to differences in the relative abundance of voles versus mice between sites and the higher level of ectoparasitism by larval I. scapularis on Peromyscus versus M. gapperi at both sites. The southern red-backed vole, M. gapperi, contributes to the enzootic maintenance of Lyme disease spirochetes in North Dakota and possibly other areas where this rodent species is abundant.

Rodents are key reservoirs of zoonotic pathogens and play an important role in disease transmission to humans. Importantly, anthropogenic land‐use change has been found to increase the abundance of rodents that thrive in human‐built environments (synanthropic rodents), particularly rodent reservoirs of zoonotic disease. Anthropogenic environments also affect the microbiome of synanthropic wildlife, influencing wildlife health and potentially introducing novel pathogens. Our objective was to examine the effect of agricultural development and synanthropic habitat on microbiome diversity and the prevalence of zoonotic bacterial pathogens in wild Peromyscus mice to better understand the role of these rodents in pathogen maintenance and transmission. We conducted 16S amplicon sequencing on faecal samples using long‐read nanopore sequencing technology to characterize the rodent microbiome. We compared microbiome diversity and composition between forest and synanthropic habitats in agricultural and undeveloped landscapes and screened for putative pathogenic bacteria. Microbiome richness, diversity, and evenness were higher in the agricultural landscape and synanthropic habitat compared to undeveloped‐forest habitat. Microbiome composition also differed significantly between agricultural and undeveloped landscapes and forest and synanthropic habitats. We detected overall low diversity and abundance of putative pathogenic bacteria, though putative pathogens were more likely to be found in mice from the agricultural landscape. Our findings show that landscape‐ and habitat‐level anthropogenic factors affect Peromyscus microbiomes and suggest that landscape‐level agricultural development may be important to predict zoonotic pathogen prevalence. Ultimately, understanding how anthropogenic land‐use change and synanthropy affect rodent microbiomes and pathogen prevalence is important to managing transmission of rodent‐borne zoonotic diseases to humans. [ABSTRACT FROM AUTHOR]

Abstract Social interactions affect physiological and pathological processes, yet their direct impact in peripheral tissues remains elusive. Recently we showed that disruption of pair bonds in monogamous Peromyscus californicus promotes lung tumorigenesis, pointing to a direct effect of bonding status in the periphery (Naderi et al., 2021). Here we show that lung transcriptomes of tumor-free Peromyscus are altered in a manner that depends on pair bonding and superseding the impact of genetic relevance between siblings. Pathways affected involve response to hypoxia and heart development. These effects are consistent with the profile of the serum proteome of bonded and bond-disrupted Peromyscus and were extended to lung cancer cells cultured in vitro, with sera from animals that differ in bonding experiences. In this setting, the species’ origin of serum (deer mouse vs FBS) is the most potent discriminator of RNA expression profiles, followed by bonding status. By analyzing the transcriptomes of lung cancer cells exposed to deer mouse sera, an expression signature was developed that discriminates cells according to the history of social interactions and possesses prognostic significance when applied to primary human lung cancers. The results suggest that present and past social experiences modulate the expression profile of peripheral tissues such as the lungs, in a manner that impacts physiological processes and may affect disease outcomes. Furthermore, they show that besides the direct effects of the hormones that regulate bonding behavior, physiological changes influencing oxygen metabolism may contribute to the adverse effects of bond disruption.

Mercury (Hg) has been extensively studied due to its impact on the environment and health, but its effects on wild mammal populations are still poorly known. Therefore, the use of biomonitors has gained importance. Our objective was to report and compare, for the first time, the amount of mercury in small mammals belonging to three trophic guilds and to provide an initial toxicology perspective in the Mezquital Valley, a critically polluted area of Central Mexico. We quantified total Hg from the hair and liver of a nectarivorous bat (Leptonycteris yerbabuenae), an insectivorous bat (Corynorhinus townsendii) and a granivorous mouse (Peromyscus melanophrys) using atomic absorption spectrometry during the dry and rainy seasons. We compared the mercury concentrations between seasons, species and matrices. In all species, the average mercury content was higher in hair than liver, and there was no correlation between matrices. There was no difference in mercury content among species. Hg concentrations in the livers of P. melanophrys and C. townsendii were lower during the dry season than the rainy season, suggesting a seasonal decline in mercury availability. All of the values detected were below the neurotoxicity threshold reported in small mammals (10 ppm); however, we propose constant monitoring of Hg in their environment and confirm the utility of these species as biomonitors.

Social interactions affect physiological and pathological processes, yet their direct impact in peripheral tissues remains elusive. Recently we showed that disruption of pair bonds in monogamous Peromyscus californicus promotes lung tumorigenesis, pointing to a direct effect of bonding status in the periphery (Naderi et al., 2021). Here we show that lung transcriptomes of tumor-free Peromyscus are altered in a manner that depends on pair bonding and superseding the impact of genetic relevance between siblings. Pathways affected involve response to hypoxia and heart development. These effects are consistent with the profile of the serum proteome of bonded and bond-disrupted Peromyscus and were extended to lung cancer cells cultured in vitro, with sera from animals that differ in bonding experiences. In this setting, the species' origin of serum (deer mouse vs FBS) is the most potent discriminator of RNA expression profiles, followed by bonding status. By analyzing the transcriptomes of lung cancer cells exposed to deer mouse sera, an expression signature was developed that discriminates cells according to the history of social interactions and possesses prognostic significance when applied to primary human lung cancers. The results suggest that present and past social experiences modulate the expression profile of peripheral tissues such as the lungs, in a manner that impacts physiological processes and may affect disease outcomes. Furthermore, they show that besides the direct effects of the hormones that regulate bonding behavior, physiological changes influencing oxygen metabolism may contribute to the adverse effects of bond disruption. [ABSTRACT FROM AUTHOR]

Deermice of the genus Peromyscus are well suited for addressing several questions of biologist interest, including the genetic bases of longevity, behavior, physiology, adaptation, and their ability to serve as disease vectors. Here, we explore a diversity outbred approach for dissecting complex traits in Peromyscus leucopus, a nontraditional genetic model system. We take advantage of a closed colony of deer-mice founded from 38 individuals and subsequently maintained for ∼40-60 generations. From 405 low-pass short-read sequenced deermice we accurate impute genotypes at 16 million single nucleotide polymorphisms. Conditional on observed genotypes simulations were conducted in which three different sized quantitative trait loci contribute to a complex trait under three different genetic models. Using a stringent significance threshold power was modest, largely a function of the percent variation attributable to the simulated quantitative trait loci, with the underlying genetic model having only a subtle impact. We additionally simulated 2,000 pseudo-individuals, whose genotypes were consistent with those observed in the genotyped cohort and carried out additional power simulations. In experiments employing more than 1,000 mice power is high to detect quantitative trait loci contributing greater than 2.5% to a complex trait, with a localization ability of ∼100 kb. We finally carried out a Genome-Wide Association Study on two demonstration traits, bleeding time and body weight, and uncovered one significant region. Our work suggests that complex traits can be dissected in founders-unknown P. leucopus colony mice and similar colonies in other systems using easily obtained genotypes from low-pass sequencing.

DNA methylation-based biomarkers of aging have been developed for humans and many other mammals and could be used to assess how stress factors impact aging. Deer mice (Peromyscus) are long-living rodents that have emerged as an informative model to study aging, adaptation to extreme environments, and monogamous behavior. In the present study, we have undertaken an exhaustive, genome-wide analysis of DNA methylation in Peromyscus, spanning different species, stocks, sexes, tissues, and age cohorts. We describe DNA methylation-based estimators of age for different species of deer mice based on novel DNA methylation data generated on highly conserved mammalian CpGs measured with a custom array. The multi-tissue epigenetic clock for deer mice was trained on 3 tissues (tail, liver, and brain). Two human-Peromyscus clocks accurately measure age and relative age, respectively. We present CpGs and enriched pathways that relate to different conditions such as chronological age, high altitude, and monogamous behavior. Overall, this study provides a first step towards studying the epigenetic correlates of monogamous behavior and adaptation to high altitude in Peromyscus. The human-Peromyscus epigenetic clocks are expected to provide a significant boost to the attractiveness of Peromyscus as a biological model.

In biparental species, in which both parents care for their offspring, the neural and endocrine mediators of paternal behavior appear to overlap substantially with those underlying maternal behavior. Little is known, however, about the roles of classical neurotransmitters, such as norepinephrine (NE), in paternal care and whether they resemble those in maternal care. We tested the hypothesis that NE facilitates the initiation of nurturant behavior toward pups in virgin male and female California mice (Peromyscus californicus), a biparental rodent. Virtually all parents in this species are attracted to familiar and unfamiliar pups, while virgins either attack, avoid, or nurture pups, suggesting that the neurochemical control of pup-related behavior changes as mice transition into parenthood. We injected virgin males and females with nepicastat, a selective dopamine β-hydroxylase inhibitor that blocks NE synthesis (75 mg/kg, i.p.), or vehicle 2 h before exposing them to a novel pup, estrous female (males only), or pup-sized novel object for 60 min. Nepicastat significantly reduced the number of males and females that approached the pup and that displayed parental behavior. In contrast, nepicastat did not alter virgins interactions with an estrous female or a novel object, suggesting that nepicastat-induced inhibition of interactions with pups was not mediated by changes in generalized neophobia, arousal, or activity. Nepicastat also significantly reduced NE levels in the amygdala and prefrontal cortex and increased the ratio of dopamine to NE in the hypothalamus. Our results suggest that NE may facilitate the initiation of parental behavior in male and female California mice.

The white-footed deermouse Peromyscus leucopus, a long-lived rodent, is a key reservoir in North America for agents of several zoonoses, including Lyme disease, babesiosis, anaplasmosis, and a viral encephalitis. While persistently infected, this deermouse is without apparent disability or diminished fitness. For a model for inflammation elicited by various pathogens, the endotoxin lipopolysaccharide (LPS) was used to compare genome-wide transcription in blood by P. leucopus, Mus musculus, and Rattus norvegicus and adjusted for white cell concentrations. Deermice were distinguished from the mice and rats by LPS response profiles consistent with non-classical monocytes and alternatively-activated macrophages. LPS-treated P. leucopus, in contrast to mice and rats, also displayed little transcription of interferon-gamma and lower magnitude fold-changes in type 1 interferon-stimulated genes. These characteristics of P. leucopus were also noted in a Borrelia hermsii infection model. The phenomenon was associated with comparatively reduced transcription of endogenous retrovirus sequences and cytoplasmic pattern recognition receptors in the deermice. The results reveal a mechanism for infection tolerance in this species and perhaps other animal reservoirs for agents of human disease.

Animals that are competent reservoirs of zoonotic pathogens commonly suffer little morbidity from the infections. To investigate mechanisms of this tolerance of infection, we used single-dose lipopolysaccharide (LPS) as an experimental model of inflammation and compared the responses of two rodents: Peromyscus leucopus, the white-footed deermouse and reservoir for the agents of Lyme disease and other zoonoses, and the house mouse Mus musculus Four hours after injection with LPS or saline, blood, spleen, and liver samples were collected and subjected to transcriptome sequencing (RNA-seq), metabolomics, and specific reverse transcriptase quantitative PCR (RT-qPCR). Differential expression analysis was at the gene, pathway, and network levels. LPS-treated deermice showed signs of sickness similar to those of exposed mice and had similar increases in corticosterone levels and expression of interleukin 6 (IL-6), tumor necrosis factor, IL-1β, and C-reactive protein. By network analysis, the M. musculus response to LPS was characterized as cytokine associated, while the P. leucopus response was dominated by neutrophil activity terms. In addition, dichotomies in the expression levels of arginase 1 and nitric oxide synthase 2 and of IL-10 and IL-12 were consistent with type M1 macrophage responses in mice and type M2 responses in deermice. Analysis of metabolites in plasma and RNA in organs revealed species differences in tryptophan metabolism. Two genes in particular signified the different phenotypes of deermice and mice: the Slpi and Ibsp genes. Key RNA-seq findings for P. leucopus were replicated in older animals, in a systemic bacterial infection, and with cultivated fibroblasts. The findings indicate that P. leucopus possesses several adaptive traits to moderate inflammation in its balancing of infection resistance and tolerance.IMPORTANCE Animals that are natural carriers of pathogens that cause human diseases commonly manifest little or no sickness as a consequence of infection. Examples include the deermouse, Peromyscus leucopus, which is a reservoir for Lyme disease and several other disease agents in North America, and some types of bats, which are carriers of viruses with pathogenicity for humans. Mechanisms of this phenomenon of infection tolerance and entailed trade-off costs are poorly understood. Using a single injection of lipopolysaccharide (LPS) endotoxin as a proxy for infection, we found that deermice differed from the mouse (Mus musculus) in responses to LPS in several diverse pathways, including innate immunity, oxidative stress, and metabolism. Features distinguishing the deermice cumulatively would moderate downstream ill effects of LPS. Insights gained from the P. leucopus model in the laboratory have implications for studying infection tolerance in other important reservoir species, including bats and other types of wildlife.

Women are more likely to suffer from stress-related affective disorders than men, but the underlying mechanisms of sex differences remain unclear. Previous works show that microRNA (miRNA) profiles are altered in stressed animals and patients with depression and anxiety disorders. In this study, we investigated how miRNA expression in the anterior bed nucleus of stria terminalis (BNST) was affected by social defeat stress in female and male California mice (Peromyscus californicus). We performed sequencing to identify miRNA transcripts in the whole brain and anterior BNST followed by qPCR analysis to compare miRNA expression between control and stressed animals. The results showed that social defeat stress induced sex-specific miRNA expression changes in the anterior BNST. Let-7a, let-7f and miR-181a-5p were upregulated in stressed female but not male mice. Our study provided evidence that social stress produces distinct molecular responses in the BNST of males and females.

Developmental exposure to endocrine disrupting chemicals (EDCs), e.g., bisphenol A (BPA) or genistein (GEN), causes longstanding epigenome effects. MicroRNAs (miRs) regulate which mRNAs will be translated to proteins and thereby serve as the final checkpoint in epigenetic control. Scant amount is known, however, whether EDCs affect neural miRNA (miR) patterns. We aimed to test the hypothesis that developmental exposure of California mice (Peromyscus californicus) to GEN, BPA, or both chemicals influences hypothalamic miR/small RNA profiles and ascertain the extent such biomolecular alterations correlate with behavioral and metabolic changes. California mice were developmentally exposed to GEN (250 mg/kg feed weight, FW), GEN (250 mg/kg FW)+BPA (5 mg/kg FW), low dose (LD) BPA (5 mg/kg FW), or upper dose (UD) BPA (50 mg/kg FW). Adult offspring were tested in a battery of behavioral and metabolic tests; whereupon, mice were euthanized, brains were collected and frozen, small RNAs were isolated from hypothalamic punches, and subsequently sequenced. California mice exposed to one or both EDCs engaged in one or more repetitive behaviors. GEN, LD BPA, and UD BPA altered aspects of ultrasonic and audible vocalizations. Each EDC exposure led to sex-dependent differences in differentially expressed miR/small RNAs with miR7-2, miR146, and miR148a being increased in all female and male EDC exposed groups. Current findings reveal that developmental exposure to GEN and/or BPA affects hypothalamic miR/small RNA expression patterns, and such changes correlate with EDC-induced behavioral and metabolic alterations. miR146 is likely an important mediator and biomarker of EDC exposure in mammals, including humans.

Social stressors are known to have strong negative impacts on mental health. There is a long history of preclinical social defeat stress studies in rodents focusing on males that has produced important insights into the neural mechanisms that modulate depression- and anxiety-related behavior. Despite these impressive results, a historical weakness of rodent social stress models has been an under-representation of studies in females. This is problematic because rates of depression and anxiety are higher in women versus men. Recently there has been a surge of interest in adapting social stress methods for female rodents. Here we review new rodent models that have investigated numerous facets of social stress in females. The different models have different strengths and weaknesses, with some model systems having stronger ethological validity with other models having better access to molecular tools to manipulate neural circuits. Continued use and refinement of these complementary models will be critical for addressing gaps in understanding the function of neural circuits modulating depression- and anxiety-related behavior in females.

Phenotypic plasticity can play an important role in the ability of animals to tolerate environmental stress, but the nature and magnitude of plastic responses are often specific to the developmental timing of exposure. Here, we examine changes in gene expression in the diaphragm of highland deer mice (Peromyscus maniculatus) in response to hypoxia exposure at different stages of development. In highland deer mice, developmental plasticity in diaphragm function may mediate changes in several respiratory traits that influence aerobic metabolism and performance under hypoxia. We generated RNAseq data from diaphragm tissue of adult deer mice exposed to (1) life‐long hypoxia (before conception to adulthood), (2) post‐natal hypoxia (birth to adulthood), (3) adult hypoxia (6–8 weeks only during adulthood) or (4) normoxia. We found five suites of co‐regulated genes that are differentially expressed in response to hypoxia, but the patterns of differential expression depend on the developmental timing of exposure. We also identified four transcriptional modules that are associated with important respiratory traits. Many of the genes in these transcriptional modules bear signatures of altitude‐related selection, providing an indirect line of evidence that observed changes in gene expression may be adaptive in hypoxic environments. Our results demonstrate the importance of developmental stage in determining the phenotypic response to environmental stressors. [ABSTRACT FROM AUTHOR]

Activation of brown adipose tissue (BAT) thermogenesis impacts energy balance and must be tightly regulated. Several neurotrophic factors, expressed in BAT of adult laboratory rodents, have been implicated in remodeling the sympathetic neural network to enhance thermogenesis [e.g., nerve growth factor (NGF), neuregulin-4 (NRG4), and S100b]. Here, we compare, to our knowledge, for the first time, the relative roles of three neurotrophic "batokines" in establishing/remodeling innervation during postnatal development and adult cold stress. We used laboratory-reared Peromyscus maniculatus, which rely heavily on BAT-based thermogenesis for survival in the wild, beginning between postnatal days (P) 8 and 10. BAT sympathetic innervation was enhanced from P6 to P10, and exogenous NGF, NRG4, and S100b stimulated neurite outgrowth from P6 sympathetic neurons. Endogenous BAT protein stores and/or gene expression of NRG4, S100b, and calsyntenin-3β (which may regulate S100b secretion) remained high and constant during development. However, endogenous NGF was low and ngf mRNA was undetectable. Conditioned media (CM) from cultured P10 BAT slices stimulated neurite outgrowth from sympathetic neurons in vitro, which was inhibited by antibodies against all three growth factors. P10 CM had significant amounts of secreted NRG4 and S100b protein, but not NGF. By contrast, BAT slices from cold-acclimated adults released significant amounts of all three factors relative to thermoneutral controls. These data suggest that although neurotrophic batokines regulate sympathetic innervation in vivo, their relative contributions differ depending on the life stage. They also provide novel insights into the regulation of BAT remodeling and BAT's secretory role, both of which are critical to our understanding of mammalian energy homeostasis. [ABSTRACT FROM AUTHOR]

Small mammals are often key components in ecological monitoring programs, and live trapping is often used to obtain small mammal density estimates or other metrics. However, an aspect of such trapping that has received little attention is opportunistic predation of captured animals. Here, we report a Common Raven (Corvus corax) preying on a deermouse (Peromyscus spp.) after it was released from a live trap. The mouse was torpid when removed from the trap. The raven preyed on the deermouse right after it was released, likely because the mouse had not yet fully aroused from torpor and was not able to find adequate shelter or evade the raven. Best practices to avoid similar occurrences include passively warming the animal before releasing it or returning it to the trap to arouse from torpor in safety. Our observation further highlights the need for researchers to be vigilant about opportunistic predation of small mammals captured and released from live traps and to take actions to mitigate the risk, especially if the mammals are exhibiting signs of torpor. [ABSTRACT FROM AUTHOR]

Many animals produce long-distance acoustic signals to mediate a variety of social interactions, and the efficacy of transmission depends in part on environmental attenuation. Vocalizing from positions that optimize transmission is one key solution to minimizing attenuation, though few studies assess the magnitude of this effect in relation to receiver position. In this study, we assessed how transmission of high-frequency vocalizations produced by pinyon mice (Peromyscus truei) varied based on the position of senders and receivers. Pinyon mice are semi-arboreal rodents that produce sustained vocalizations to advertise to conspecifics. Synthesized signals derived from a population-sample-average of fundamental frequency, duration, and amplitude were broadcast and recorded at different heights (0, 1, and 2 m) and distances (1, 2, 4, and 8 m) in a full factorial design to mimic hypothetical senders and receivers. We also measured receiver hearing sensitivity using auditory brainstem responses (ABR) to quantify the audible distance (active space) of vocalizations at different heights. Vocalizations showed less attenuation when emitted and received from an elevation compared to the ground if the signal was received at least 4 m from the sender. Vocalizations emitted from a 1 m height had an approximately 3 times greater audible distance compared to the ground. Additionally, less attenuation occurred when both senders and receivers were elevated at the same height and when receivers were elevated, regardless of sender height. Our results highlight the importance of considering receiver position in animal communication, especially when senders produce highly directional signals. Significance statement: Vocalizing animals often position themselves in locations that maximize sound transmission. However, the magnitude of this effect is not often quantified, especially in relation to the position of intended receivers. In this study, we combined acoustic recording, hearing experiments, and modelling of sound attenuation to quantify how sending and receiving vocalizations from trees impacts sound transmission in a semi-arboreal mouse. We found that vocalizations produced from 1 m above the ground could be heard by receivers at 3 times the distance compared to ground level. We also found that no matter the sender position, receivers benefitted from being at elevated positions. Finally, we found that the least attenuation occurred when senders and receivers were elevated at the same height. Our results highlight the importance of considering receiver position in animal communication, especially when senders produce highly directional signals. [ABSTRACT FROM AUTHOR]

Environmental hypoxia challenges female reproductive physiology in placental mammals, increasing rates of gestational complications. Adaptation to high elevation has limited many of these effects in humans and other mammals, offering potential insight into the developmental processes that lead to and protect against hypoxia-related gestational complications. However, our understanding of these adaptations has been hampered by a lack of experimental work linking the functional, regulatory, and genetic underpinnings of gestational development in locally adapted populations. Here, we dissect high-elevation adaptation in the reproductive physiology of deer mice (Peromyscus maniculatus), a rodent species with an exceptionally broad elevational distribution that has emerged as a model for hypoxia adaptation. Using experimental acclimations, we show that lowland mice experience pronounced fetal growth restriction when challenged with gestational hypoxia, while highland mice maintain normal growth by expanding the compartment of the placenta that facilitates nutrient and gas exchange between gestational parent and fetus. We then use compartment-specific transcriptome analyses to show that adaptive structural remodeling of the placenta is coincident with widespread changes in gene expression within this same compartment. Genes associated with fetal growth in deer mice significantly overlap with genes involved in human placental development, pointing to conserved or convergent pathways underlying these processes. Finally, we overlay our results with genetic data from natural populations to identify candidate genes and genomic features that contribute to these placental adaptations. Collectively, these experiments advance our understanding of adaptation to hypoxic environments by revealing physiological and genetic mechanisms that shape fetal growth trajectories under maternal hypoxia. [ABSTRACT FROM AUTHOR]

Background. Animals rely on sound for daily activities, and anthropogenic noise is a pollutant that alters the natural soundscape within which they are active. As human infrastructure expands, broadband anthropogenic noise increases, which can affect behaviors of nocturnal animals. Mice are nocturnal animals that produce ultrasonic calls as part of their behavioral repertoire. Methods. We assessed effects of anthropogenic and natural noise on the behaviors of wild deer mice (Peromyscus maniculatus) and woodland jumping mice (Napaeozapus insignis), two species of mice that produce ultrasonic calls. We measured activity, foraging behavior at a foraging tray, and calling behavior to broadcasts of natural and anthropogenic noise, compared to a baseline with no broadcasting, at 25 focal areas in the Southern Appalachian Mountain Range of North Carolina, USA. Results. Deer mice exposed to anthropogenic noise spent less time in focal areas with broadcasted anthropogenic noise. Mice took longer to begin foraging in the presence of anthropogenic noise, they spent less time at the foraging tray, and left fewer husks but consumed the same number of seeds as mice exposed to natural noise. Deer mice were less likely than woodland jumping mice to be the first to enter the focal area and approach food when in the presence of anthropogenic noise. Both species produced few ultrasonic calls in the presence of broadcasted natural and anthropogenic noise compared to their baseline level of calling. We present the first calls recorded from woodland jumping mice. Conclusion. Anthropogenic noise affects activity, foraging behavior, and calling behavior of nocturnal mice. Natural noise also affects the calling behavior of mice. Mouse species respond differently to anthropogenic noise, with deer mice appearing more sensitive to anthropogenic noise than woodland jumping mice. Responses to noise could have important effects on the ecology of mice and these two species respond differently. Species differences should be considered when mitigating the effects of noise in conservation ecology. [ABSTRACT FROM AUTHOR]

Retrotransposon families in the rodent family Cricetidae have been understudied in contrast to Muridae, both taxa classified within the superfamily Muroidea. Therefore, we carried out a study to advance our knowledge of the unique mys LTR-retroelement identified in Peromyscus leucopus, by incorporating intra-ORF PCR, quantitative dot blots, DNA and protein library screens, the generation of molecular phylogenies, and analyses of orthologous LTR-retroelement loci. These analyses led to the discovery of three additional related families of LTR-retroelements, which include a 2900 bp full-length element of mys-related sequences (mysRS), an 8000 bp element containing the mys ORF1 sequence (mORF1) with ERV-related sequences downstream in the reverse orientation, as well as an 1800 bp element primarily consisting of mys ORF2 (mORF2) related sequences flanked by LTRs. Our data revealed only a few full-length mys elements among genera of the Neotominae subfamily of cricetid rodents, most existing as partial copies. The mysRS and mORF1 elements are also limited to the genomes of the Neotominae subfamily, whereas mORF2 appears to be restricted to the Peromyscus genus. Molecular phylogenies demonstrating concerted evolution along with an assessment of orthologous loci in Peromyscus for the presence or absence of elements are consistent with activity of these novel LTR-retroelement families within this genus. Together with known activity of various families of non-LTR retroelements in Peromyscus species, we propose that retrotransposons have been continually contributing to the dynamics of Peromyscus genomes promoting genomic diversity and may be correlated with the evolution of more than 50 identified Peromyscus species. [ABSTRACT FROM AUTHOR]

Oxytocin increases the salience of both positive and negative social contexts and it is thought that these diverse actions on behavior are mediated in part through circuit-specific action. This hypothesis is based primarily on manipulations of oxytocin receptor function, leaving open the question of whether different populations of oxytocin neurons mediate different effects on behavior. Here we inhibited oxytocin synthesis in a stress-sensitive population of oxytocin neurons specifically within the medioventral bed nucleus of the stria terminalis (BNSTmv). Oxytocin knockdown prevented social stress-induced increases in social vigilance and decreases in social approach. Viral tracing of BNSTmv oxytocin neurons revealed fibers in regions controlling defensive behaviors, including lateral hypothalamus, anterior hypothalamus, and anteromedial BNST (BNSTam). Oxytocin infusion into BNSTam in stress naïve mice increased social vigilance and reduced social approach. These results show that a population of extrahypothalamic oxytocin neurons plays a key role in controlling stress-induced social anxiety behaviors.

Our review focuses on findings from mammals as part of a Special Issue "30th Anniversary of the Challenge Hypothesis". Here we put forth an integration of the mechanisms through which testosterone controls territorial behavior and consider how reproductive experience may alter these mechanisms. The emphasis is placed on the function of socially induced increases in testosterone (T) pulses, which occur in response to social interactions, as elegantly developed by Wingfield and colleagues. We focus on findings from the monogamous California mouse, as data from this species shows that reproductive status is a key factor influencing social interactions, site fidelity, and vigilance for offspring defense. Specifically, we examine differences in T pulses in sexually naïve versus sexually experienced pair bonded males. Testosterone pulses influence processes such as social decision making, the winner-challenge effect, and location preferences through rewarding effects of T. We also consider how social and predatory vigilance contribute to T pulses and how these interactions contribute to a territory centered around maximizing reproduction. Possible underlying mechanisms for these effects include the nucleus accumbens (rewarding effects of testosterone), hippocampus (spatial memories for territories), and the bed nucleus of the stria terminalis (social vigilance). The development of the challenge effect has provided an ideal framework for understanding the complex network of behavioral, environmental, physiological and neural mechanisms that ultimately relates to competition and territoriality across taxa. The opportunity to merge research on the challenge effect using both laboratory and field research to understand social behavior is unparalleled.

The cricetine rodent Peromyscus leucopus is an important reservoir for several human zoonoses, including Lyme disease, in North America. Akin to hamsters, the white-footed deermouse has been unevenly characterized in comparison to the murid Mus musculus. To further understanding of P. leucopus' total genomic content, we investigated gut microbiomes of an outbred colony of P. leucopus, inbred M. musculus, and a natural population of P. leucopus. Metagenome and whole genome sequencing were combined with microbiology and microscopy approaches. A focus was the genus Lactobacillus, four diverse species of which were isolated from forestomach and feces of colony P. leucopus. Three of the species-L. animalis, L. reuteri, and provisionally-named species "L. peromysci"-were identified in fecal metagenomes of wild P. leucopus but not discernibly in samples from M. musculus. L. johnsonii, the fourth species, was common in M. musculus but absent or sparse in wild P. leucopus. Also identified in both colony and natural populations were a Helicobacter sp. in feces but not stomach, and a Tritrichomonas sp. protozoan in cecum or feces. The gut metagenomes of colony P. leucopus were similar to those of colony M. musculus at the family or higher level and for major subsystems. But there were multiple differences between species and sexes within each species in their gut metagenomes at orthologous gene level. These findings provide a foundation for hypothesis-testing of functions of individual microbial species and for interventions, such as bait vaccines based on an autochthonous bacterium and targeting P. leucopus for transmission-blocking.

We demonstrate that 6 distinct Peromyscus rodent species are permissive to experimental infection with Sin Nombre orthohantavirus (SNV). Viral RNA and SNV antibodies were detected in members of all 6 species. P. leucopus mice demonstrated markedly higher viral and antibody titers than P. maniculatus mice, the established primary hosts for SNV.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the virus that causes coronavirus disease-19 (COVID-19), emerged in late 2019 in Wuhan, China and its rapid global spread has resulted in millions of deaths. An important public health consideration is the potential for SARS-CoV-2 to establish endemicity in secondary animal reservoirs outside of Asia or acquire adaptations that result in new variants with the ability to evade the immune response and reinfect the human population. Previous work has shown that North American deer mice (Peromyscus maniculatus) are susceptible and can transmit SARS-CoV-2 to naïve conspecifics, indicating its potential to serve as a wildlife reservoir for SARS-CoV-2 in North America. In this study, we report experimental SARS-CoV-2 susceptibility of two additional subspecies of the North American deer mouse and two additional deer mouse species, with infectious virus and viral RNA present in oral swabs and lung tissue of infected deer mice and neutralizing antibodies present at 15 days post-challenge. Moreover, some of one species, the California mouse (P. californicus) developed clinical disease, including one that required humane euthanasia. California mice often develop spontaneous liver disease, which may serve as a comorbidity for SARS-CoV-2 severity. The results of this study suggest broad susceptibility of rodents in the genus Peromyscus and further emphasize the potential of SARS-CoV-2 to infect a wide array of North American rodents. [ABSTRACT FROM AUTHOR]

Background Animals rely on sound to mediate a myriad of daily activities, and anthropogenic noise is a pollutant that alters the natural soundscape within which they are active. As human infrastructure expands, broadband anthropogenic noise increases, which can affect behaviors of free-living nocturnal animals. Mice are nocturnal animals that produce ultrasonic calls as part of their behavioral repertoire. Methods We assessed effects of anthropogenic and natural noise on the behaviors of wild deer mice (Peromyscus maniculatus) and woodland jumping mice (Napaeozapus insignis), two species of mice that produce ultrasonic calls. We measured activity, foraging behavior at a foraging tray, and calling behavior to broadcasts of natural and anthropogenic noise, compared to a baseline with no broadcasting, at 25 focal areas in the Southern Appalachian Mountain Range of North Carolina, USA. Results Deer mice exposed to anthropogenic noise spent less time in focal areas with broadcasted anthropogenic noise. Mice took longer to begin foraging in the presence of anthropogenic noise, they spent less time at the foraging tray, and left fewer husks but consumed the same number of seeds as mice exposed to natural noise. Deer mice were less likely than woodland jumping mice to be the first to enter the focal area and approach food when in the presence of anthropogenic noise. Both species produced few ultrasonic calls in the presence of broadcasted natural and anthropogenic noise compared to their baseline level of calling. We present the first calls recorded from woodland jumping mice. Conclusion Anthropogenic noise affects activity, foraging behavior, and calling behavior of nocturnal mice. Natural noise also affects the calling behavior of mice. Mouse species respond differently to anthropogenic noise, with deer mice appearing more sensitive to anthropogenic noise than woodland jumping mice. Responses to noise could have important effects on the ecology of mice and these two species respond differently. Species differences should be considered when mitigating the effects of noise in conservation ecology.

Placentophagia increases parental motivation in sexually inexperienced adult female rodents. We hypothesized that placenta ingestion has similar effects in virgin male California mice (Peromyscus californicus), a monogamous rodent in which fathers provide extensive care for their offspring. To test this hypothesis, we administered either a conspecific's placenta in oil or oil alone to adult virgin males via oral gavage. One, 7 or 24 hours later, each male underwent a 1-hour behavior test with either an unfamiliar pup or a novel object marble), immediately after which the mouse was perfused and the brain collected. Neural activation (Fos-immunoreactivity) was quantified in brain regions involved in parental care (bed nucleus of the stria terminalis, medial preoptic area, amygdala). We found few significant effects of placenta treatment, but at 7 h post-gavage, placenta-treated males had decreased latencies to approach both pups and marbles, compared to oil-treated controls (p = 0.05). Placenta-treated males also showed lower Fos-immunoreactivity in the dorsal bed nucleus of the stria terminalis, irrespective of stimulus type, compared to controls, both 1 h (p = 0.04) and 7 h (p = 0.05) post-treatment. These results suggest that placentophagia does not directly affect paternal motivation but might increase willingness to interact with novel stimuli in virgin male California mice.

Motherhood is energetically costly for mammals and is associated with pronounced changes in mothers' physiology, morphology and behavior. In ~5% of mammals, fathers assist their mates with rearing offspring and can enhance offspring survival and development. Although these beneficial consequences of paternal care can be mediated by direct effects on offspring, they might also be mediated indirectly, through beneficial effects on mothers. We tested the hypothesis that fathers in the monogamous, biparental California mouse (Peromyscus californicus) reduce the burden of parental care on their mates, and therefore, that females rearing offspring with and without assistance from their mates will show differences in endocrinology, morphology and behavior, as well as in the survival and development of their pups. We found that pups' survival and development in the lab did not differ between those raised by a single mother and those reared by both mother and father. Single mothers spent more time in feeding behaviors than paired mothers. Both single and paired mothers had higher lean mass and/or lower fat mass and showed more anxiety-like behavior in open-field tests and tail-suspension tests, compared to non-breeding females. Single mothers had higher body-mass-corrected liver and heart masses, but lower ovarian and uterine masses, than paired mothers and/or non-breeding females. Mass of the gastrointestinal tract did not differ between single and paired mothers, but single mothers had heavier gastrointestinal tract compared to non-breeding females. Single motherhood also induced a flattened diel corticosterone rhythm and a blunted corticosterone response to stress, compared to non-breeding conditions. These findings suggest that the absence of a mate induces morphological and endocrine changes in mothers, which might result from increased energetic demands of pup care and could potentially help maintain normal survival and development of pups.

California mice (Peromyscus californicus) differ from most other mammals in that they are biparental, genetically monogamous, and (compared with other Peromyscus) relatively large. We evaluated effects of cold acclimation on metabolic rate, exercise performance, and morphology of pair-housed male California mice, as well as modulation of these effects by fatherhood. In Experiment 1, virgin males housed at 5° or 10 °C for approximately 25 days were compared with virgins housed at standard vivarium temperature of 22 °C. Measures included resting metabolic rate (RMR), maximal oxygen consumption ([Formula: see text]max), grip strength, and sprint speed. In Experiment 2, virgin males housed at 22 °C were compared with three groups of males housed at 10 °C: virgins, breeding males (housed with a female and their pups), and non-breeding males (housed with an ovariectomized, estrogen- and progesterone-treated female) after long-term acclimation (mean 243 days). Measures in this experiment included basal metabolic rate (BMR), [Formula: see text]max, maximal thermogenic capacity ([Formula: see text]sum), and morphological traits. In Experiment 1, virgin males housed at 5° and 10 °C had higher RMR and [Formula: see text]max than those at 22 °C. In Experiment 2, 10 °C-acclimated groups had shorter bodies; increased body, fat, and lean masses; higher BMR and [Formula: see text]sum, and generally greater morphometric measures and organ masses than virgin males at 22 °C. Among the groups housed at 10 °C, breeding males had higher BMR and lower [Formula: see text]max than non-breeding and/or virgin males. Overall, we found that effects of fatherhood during cold acclimation were inconsistent, and that several aspects of cold acclimation differ substantially between California mice and other small mammals.

The rodent Peromyscus leucopus is the natural reservoir of several tick-borne infections, including Lyme disease. To expand the knowledge base for this key species in life cycles of several pathogens, we assembled and scaffolded the P. leucopus genome. The resulting assembly was 2.45 Gb in total length, with 24 chromosome-length scaffolds harboring 97% of predicted genes. RNA sequencing following infection of P. leucopus with Borreliella burgdorferi, a Lyme disease agent, shows that, unlike blood, the skin is actively responding to the infection after several weeks. P. leucopus has a high level of segregating nucleotide variation, suggesting that natural resistance alleles to Crispr gene targeting constructs are likely segregating in wild populations. The reference genome will allow for experiments aimed at elucidating the mechanisms by which this widely distributed rodent serves as natural reservoir for several infectious diseases of public health importance, potentially enabling intervention strategies.

Parental care by fathers enhances offspring survival and development in numerous species. In the biparental California mouse, Peromyscus californicus, behavioral plasticity is seen during the transition into fatherhood: adult virgin males often exhibit aggressive or indifferent responses to pups, whereas fathers engage in extensive paternal care. In this species and other biparental mammals, the onset of paternal behavior is associated with increased neural responsiveness to pups in specific brain regions, including the medial preoptic area of the hypothalamus (MPOA), a region strongly implicated in both maternal and paternal behavior. To assess possible changes in neural circuit properties underlying this increased excitability, we evaluated synaptic, intrinsic, and morphological properties of MPOA neurons in adult male California mice that were either virgins or first-time fathers. We used standard whole-cell recordings in a novel in vitro slice preparation. Excitatory and inhibitory post-synaptic currents from MPOA neurons were recorded in response to local electrical stimulation, and input/output curves were constructed for each. Responses to trains of stimuli were also examined. We quantified intrinsic excitability by measuring voltage changes in response to square-pulse injections of both depolarizing and hyperpolarizing current. Biocytin was injected into neurons during recording, and their morphology was analyzed. Most parameters did not differ significantly between virgins and fathers. However, we document a decrease in synaptic inhibition in fathers. These findings suggest that the onset of paternal behavior in California mouse fathers may be associated with limited electrophysiological plasticity within the MPOA.

Social monogamy, typically characterized by the formation of a pair bond, increased territorial defense, and often biparental care, has independently evolved multiple times in animals. Despite the independent evolutionary origins of monogamous mating systems, several homologous brain regions and neuropeptides and their receptors have been shown to play a conserved role in regulating social affiliation and parental care, but little is known about the neuromolecular mechanisms underlying monogamy on a genomic scale. Here, we compare neural transcriptomes of reproductive males in monogamous and nonmonogamous species pairs of Peromyscus mice, Microtus voles, parid songbirds, dendrobatid frogs, and Xenotilapia species of cichlid fishes. We find that, while evolutionary divergence time between species or clades did not explain gene expression similarity, characteristics of the mating system correlated with neural gene expression patterns, and neural gene expression varied concordantly across vertebrates when species transition to monogamy. Our study provides evidence of a universal transcriptomic mechanism underlying the evolution of monogamy in vertebrates.

The cricetine rodents Peromyscus leucopus and P. maniculatus are key reservoirs for several zoonotic diseases in North America. We determined the complete circular mitochondrial genome sequences of representatives of 3 different stock colonies of P. leucopus, one stock colony of P. maniculatus and two wild populations of P. leucopus. The genomes were syntenic with that of the murids Mus musculus and Rattus norvegicus. Phylogenetic analysis confirmed that these two Peromyscus species are sister taxa in a clade with P. polionotus and also uncovered a distinction between P. leucopus populations in the eastern and the central United States. In one P. leucopus lineage four extended regions of mitochondrial pseudogenes were identified in the nuclear genome. RNA-seq analysis revealed transcription of the entire genome and differences from controls in the expression profiles of mitochondrial genes in the blood, but not in liver or brain, of animals infected with the zoonotic pathogen Borrelia hermsii. PCR and sequencing of the D-loop of the mitochondrion identified 32 different haplotypes among 118 wild P. leucopus at a Connecticut field site. These findings help to further establish P. leucopus as a model organism for studies of emerging infectious diseases, ecology, and in other disciplines.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the virus that causes coronavirus disease-19 (COVID-19), emerged in late 2019 in Wuhan, China and its rapid global spread has resulted in millions of deaths. An important public health consideration is the potential for SARS-CoV-2 to establish endemicity in secondary animal reservoirs outside of Asia or acquire adaptations that result in new variants with the ability to evade the immune response and reinfect the human population. Previous work has shown that North American deer mice (Peromyscus maniculatus) are susceptible and can transmit SARS-CoV-2 to naïve conspecifics, indicating its potential to serve as a wildlife reservoir for SARS-CoV-2 in North America. In this study, we report experimental SARS-CoV-2 susceptibility of two additional subspecies of the North American deer mouse and two additional deer mouse species, with infectious virus and viral RNA present in oral swabs and lung tissue of infected deer mice and neutralizing antibodies present at 15 days post-challenge. Moreover, some of one species, the California mouse (P. californicus) developed clinical disease, including one that required humane euthanasia. California mice often develop spontaneous liver disease, which may serve as a comorbidity for SARS-CoV-2 severity. The results of this study suggest broad susceptibility of rodents in the genus Peromyscus and further emphasize the potential of SARS-CoV-2 to infect a wide array of North American rodents.

The coexistence of competing species requires density feedbacks that have a larger effect on their own species' population growth than they do on others in the assembly. The feedbacks are often associated with behavioral tradeoffs that enable species to differentially exploit underlying axes of heterogeneity. Conjoining theories of species coexistence with foraging behavior and density‐dependent habitat selection reveals that such tradeoffs impinge on invasion probabilities and equilibrium dynamics emerging from species' differences in habitat use. The resulting habitat separation promotes coexistence by reducing the overall interaction among species. Differential habitat selection depends on the behavioral abilities of organisms to identify and exploit the most profitable habitats and resource patches. One might thus expect that each species will evolve behavioral types distinct from those of other potential competitors. Accordingly, we exposed four coexisting species in four genera of boreal rodents to open‐field tests. We used principal components (PC) to summarize their behaviors along three independent axes corresponding with clines of exploratory, vigilant, and apprehensive personalities. We confirmed that the axes represented repeatable behaviors (personalities) and assessed differences among species with a general linear model (GLM). The GLM revealed highly distinct differences among species, and between pairs of species, on each PC. Even so, it is difficult to infer the adaptive advantages of personality to the habitat segregation that reduces otherwise high interactions among species. Rather, personalities are best interpreted as co‐adaptive behaviors reflecting the complex of morphological, physiological and behavioral attributes that dictate tradeoffs and enable coexistence. [ABSTRACT FROM AUTHOR]

Peromyscus maniculatus, including the laboratory stock BW, have been used as a model organism for autism spectrum disorder and obsessive–compulsive disorder because of the high occurrence of stereotypy. Several studies have identified neurological and environmental components of the phenotype; however, the heritability of the phenotype has not been examined. This study characterizes the incidence and heritability of vertical jumping stereotypy (VS) and backflipping (BF) behavior in the BW stock of the Peromyscus Genetic Stock Center, which are indicative of autism spectrum disorders. In addition, interspecies crosses between P. maniculatus and P. polionotus were also performed to further dissect genetically stereotypic behavior. The inheritance pattern of VS suggests that multiple genes result in a quantitative trait with low VS being dominant over high VS. The inheritance pattern of BF suggests that fewer genes are involved, with one allele causing BF in a dominant fashion. An association analysis in BW could reveal the underlying genetic loci associated with stereotypy in P. maniculatus, especially for the BF behavior. [ABSTRACT FROM AUTHOR]

Hooper's deer mouse, Peromyscus hooperi, is the sole member of the Peromyscus hooperi species group. This species is endemic to México where it is restricted to the grassland transition zone in the states of Coahuila, Zacatecas, and San Luis Potosí. Previous studies using mitochondrial and nuclear genes (Cytb, Adh1-I2, Fgb-I7 and Rbp3) did not resolve the phylogenetic relationships of this relatively poorly known species. It was hypothesized that P. hooperi is sister to P. crinitus, and these two taxa are related to P. melanotis, P. polionotus, P. maniculatus, P. keeni, P. leucopus, P. gossypinus, P. eremicus, P. californicus, and Osgoodomys banderanus. Based on morphological characters, karyotypes, and allozymes, P. hooperi does not align with either subgenera Haplomylomys or Peromyscus. However, its unique characteristics (e. g., phallus, karyotype) have been recognized, and therefore it has been retained as its own species group. To better resolve the phylogenetic placement of P. hooperi, we performed target-enrichment and high-throughput sequencing and obtained several thousand nuclear ultraconserved elements and a complete mitogenome from a specimen collected in 1896 by Nelson and Goldman in Coahuila, México. We compared these data with 21 other species of neotomines using genome-wide data. Contrary to previous studies, we found high nodal support for the placement of P. hooperi as sister to a clade that includes Podomys floridanus, Neotomodon alstoni, Habromys simulatus, H. ixtlani, Peromyscus mexicanus, P. megalops, P. melanophrys, P. perfulvus, P. aztecus, P. attwateri, P. pectoralis, and P. boylii. We dated a Pliocene divergence of P. hooperi from its sister group at approximately 3.98 mya, and after the split of P. crinitus at ca. 4.31 mya from other peromyscines. We demonstrated that genome-wide data improve the phylogenetic signal, independently of taxon sampling, for a phylogenetically problematic species such as P. hooperi. We recommend that future genomic studies expand taxon sampling, including members of the subgenus Haplomylomys, to confirm the phylogenetic relationships of P. hooperi and the genetic status of its populations. El ratón de Hooper Peromyscus hooperi, es el único miembro del grupo de especies que lleva su mismo nombre. Es una especie endémica de México que se encuentra restringida a las zonas de transición de pastizales en los estados de Coahuila, Zacatecas y San Luis Potosí. Estudios previos en los que se han analizado genes mitocondriales y nucleares (Cytb, Adh1-I2, Fgb-I7 y Rbp3) no han podido resolver las relaciones filogenéticas de esta especie poco conocida. Sin embargo, se ha sugerido que P. hooperi podría ser la especie hermana de P. crinitus, y estar cercanamente relacionada con P. melanotis, P. polionotus, P. maniculatus, P. keeni, P. leucopus, P. gossypinus, P. eremicus, P. californicus y Osgoodomys banderanus. Con base en datos morfológicos, cariotipos y aloenzimas, no se ha podido determinar si esta especie se encuentra más estrechamente relacionada con el subgénero Haplomylomys o Peromyscus. Sin embargo, las características únicas de P. hooperi (e. g., falo, cariotipo) han sido reconocidas, por lo que se ha mantenido en su propio grupo de especies. Con el objetivo de proveer nueva evidencia sobre la posición filogenética de P. hooperi, utilizamos el método de captura por hibridación y secuenciación masiva para obtener miles de elementos ultraconservados y el genoma mitocondrial de un ejemplar colectado en 1896 por Nelson y Goldman en Coahuila, México. Además, analizamos datos genómicos de 21 especies de neotominos. Contrario a estudios previos, encontramos altos valores de soporte en el nodo que posiciona a P. hooperi como la especie hermana del clado que incluye a Podomys floridanus, Neotomodon alstoni, Habromys simulatus, H. ixtlani, Peromyscus mexicanus, P. megalops, P. melanophrys, P. perfulvus, P. aztecus, P. attwateri, P. pectoralis y P. boylii. Datamos la divergencia de P. hooperi de su grupo hermano hace aproximadamente 3.98 millones de años, después de la divergencia de P. crinitus y de otros peromiscinos hace aproximadamente 4.31 millones de años, ambos eventos durante el Plioceno. Nuestro estudio es un claro ejemplo de que analizar datos a nivel del genoma mejoran la señal filogenética, independientemente del número de taxones, para especies cuyas relaciones filogenéticas son conflictivas o se encuentran poco resueltas como en el caso de P. hooperi. Sin embargo, recomendamos que futuros estudios genómicos incluyan un muestreo taxonómico más amplio, sobre todo de miembros del subgénero Haplomylomys, para confirmar las relaciones filogenéticas de P. hooperi y el estatus genético de sus poblaciones. [ABSTRACT FROM AUTHOR]

The Costa Rican highlands are considered hotspots of diversity and endemism, but studies on rodents are scarce. We compared the richness and abundance of mice between the montane forest and the paramo at the summit of the Talamanca mountain range. We selected two study sites within the Talamanca mountain range: the Cerro de la Muerte Biological Station and the paramo. The former is a montane forest dominated by oaks, and the latter is dominated by an herbaceous layer, and some scattered bushy patches. We captured mice in two different microhabitats within each montane forest and paramo, so we had four different sampling microhabitats: (1) paramo--bush, (2) paramo--Chusquea, (3) montane forest--bush, and (4) montane forest--Chusquea. Mice were marked to identify recaptures. We captured four mouse species and their abundance varied largely between habitats and among microhabitats (Table 1). The most abundant species, representing 85 % of all mouse captures, was Peromyscus nudipes. Mice were more abundant in the montane forest than in the paramo. Within the montane forest, mice were more abundant in the microhabitat containing bushes. The montane forest has a more complex vegetation structure with more diversity of food resources and shelters than the paramo. As well as at the habitat level, we argue that differences in abundance among microhabitats are directly related with the structure of vegetation. A more complex habitat structure may provide rodents with better conditions. Las tierras altas de Costa Rica son consideradas un punto caliente de diversidad y endemismo, pero los estudios sobre roedores son escasos. Comparamos la riqueza y abundancia de ratones entre el bosque de robledal y el páramo en la cima de la Cordillera de Talamanca. Seleccionamos dos sitios de estudio en la Cordillera de Talamanca: la Estación Biológica Cerro de la Muerte y el páramo. El primero es un bosque montano dominado por robles, y el segundo está dominado por una vegetación herbácea y algunos parches dispersos de arbustos. Capturamos ratones en dos microhábitats diferentes en el robledal y el páramo. Por lo que tuvimos cuatro microhábitats de muestreo: (1) páramo--arbustos, (2) páramo--Chusquea, (3) bosque montano--arbustos, y (4) bosque montano--Chusquea. Los ratones fueron marcados para identificar recapturas. Capturamos cuatro especies de ratones y sus abundancias variaron considerablemente entre hábitats y microhábitats (Tabla 1). La especie más abundante, con 85 % del total de capturas, fue Peromyscus nudipes. Los ratones fueron más abundantes en el robledal que en el páramo. Dentro del robledal, los ratones fueron más abundantes en el microhábitat compuesto por arbustos. El bosque montano posee una estructura vegetal más compleja, con mayor diversidad de recursos alimenticios y refugios que el páramo. Al igual que a nivel de hábitat, discutimos que las diferencias en abundancia entre microhábitats están directamente relacionadas con la estructura de la vegetación. Un hábitat con una estructura más compleja es de esperar que provea a los roedores de mejores condiciones. [ABSTRACT FROM AUTHOR]

Context: Vector-borne diseases have caused global pandemics and were responsible for more human deaths than all other causes combined in prior centuries. In the past 60 years, prevention and control programs have helped reduce human mortality from vector-borne diseases, but impacts of those control programs on wildlife populations are not well documented. Insecticides are used to reduce vector-borne diseases in several critically endangered animal populations. Although insecticides are often effective at controlling targeted vectors, their effects on non-target species have rarely been examined. Aims: To evaluate the impact of deltamethrin (an insecticide) on sympatric non-target species in areas affected by sylvatic plague, a lethal flea-borne zoonosis. Methods: We compared flea control and the effect of deltamethrin application on survival of non-target small mammals (Peromyscus maniculatus , Chaetodipus hispidus , Microtus spp., and Reithrodontomys megalotis) at three study locations in South Dakota, Colorado, and Idaho, USA. Key results: Deltamethrin treatments were more effective in reducing fleas on P. maniculatus and Microtus spp. than C. hispidus. Following burrow, nest, and bait-station applications of deltamethrin dust, apparent small mammal survival was greater for non-treatment animals than for flea-reduction animals. However, the magnitude of the difference between treated and non-treated animals differed among host species, study location, time interval, and treatment application method. Conclusions: Our results suggest that considering the impact of deltamethrin on co-occurring non-target species before widespread application in future insecticide applications is warranted. Implications: Insecticide application methods warrant consideration when designing plague management actions. Insecticides are applied worldwide as a tool to control both wildlife and/or human diseases but we need to document the impact these chemicals have on non-target animals. We examined and discovered that deltamethrin (an insecticide used to control flea vectors of the plague bacterium) reduced survival of non-target small animals in three different study sites in the western United States. Insecticides are an important tool to conserve species threated by wildlife diseases, but we need to consider and evaluate their effects on non-target animals when making management decisions regarding the best methods to reduce disease prevalence. Photograph by Amanda R. Goldberg. [ABSTRACT FROM AUTHOR]

Kappa opioid receptor activation has been linked to stress and anxiety behavior, thus leading to kappa antagonists being popularized in research as potential anxiolytics. However, while these findings may hold true in standard models, the neuromodulatory effects of social defeat may change the behavioral outcome of kappa opioid receptor activation. Previous research has shown that social defeat can lead to hyperactivity of serotonergic neurons in the dorsal raphe nucleus, and that inhibition of this increase blocks the social deficits caused by defeat. Kappa opioid receptor activation in the dorsal raphe nucleus works to decrease serotonergic activity. We injected the kappa opioid receptor U50,488 directly into the dorsal raphe nucleus of male and female, defeat and control adult California mice. Here we show evidence that U50,488 induces anxiety behavior in control male California mice, but helps relieve it in defeated males. Consistent with previous literature, we find little effect in females adding evidence that there are marked and important sex differences in the kappa opioid system.

Ingestion of placenta by mammalian mothers can lead to changes in pain sensitivity, hormone levels, and behavioral responses to newborns. In some biparental mammals, males, in addition to females, ingest placenta when their offspring are born. In the monogamous, biparental California mouse (Peromyscus californicus), males first become attracted to placenta when cohabitating with their pregnant mate, and virgin males administered placenta are less neophobic than males given oil vehicle. In this study, we investigated the effects of placentophagia on pain sensitivity, anxiety-like behavior, behavioral responses to pups, and circulating corticosterone levels of both breeding and nonbreeding male California mice. We orally administered either a conspecific placenta or oil vehicle to male mice from three reproductive conditions (first-time fathers, first-time expectant fathers, and virgin males) and tested their pain sensitivity 1 h later, as well as their exploratory behavior and paternal responsiveness in an open field 4 h post-treatment. We measured plasma corticosterone immediately after the open-field test. We found that placenta-treated males, independent of reproductive condition, traveled significantly longer distances in the open field than males treated with oil, indicative of lower anxiety. Additionally, fathers had shorter latencies to approach and to care for pups (i.e., huddling and licking pups), and spent more time engaging in these behaviors, than did age-matched expectant fathers and virgin males, independent of treatment. We found no effect on plasma corticosterone levels or pain sensitivity as a result of either treatment or reproductive condition. These findings indicate that placenta ingestion decreases anxiety-related behaviors in male California mice, but might not influence pain sensitivity, paternal responsiveness, or plasma corticosterone concentrations.