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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]

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]

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]

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]

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]

Ecologists have long debated the relative importance of biotic interactions versus species‐specific habitat preferences in shaping patterns of ecological dominance. In western North America, cycles of fire disturbance are marked by transitions between North American deermice (Peromyscus maniculatus), which predominate after wildfires, and southern red‐backed voles (Myodes gapperi), which gradually replace deermice 3–4 years postfire and maintain dominance as forests mature. While this shift has been frequently documented, the processes that mediate this turnover are debated. One possibility is competitive release, which predicts a reduction in vole competition may contribute to niche expansion and population growth in deermice. Alternatively, turnover in both species may be shaped by differences in their preferred habitat and resource base, as predicted by optimum foraging theory. We evaluate these hypotheses using stable isotopes and spatial mark–recapture of deermouse and vole populations sampled prior to and following a fire as part of a longitudinal study in the Greater Yellowstone Ecosystem. Fire disturbance was associated with a 94% decrease in vole abundance but a 102% increase in deermice. Even after accounting for microhabitat, vole and deermouse populations were negatively correlated spatially and temporally (R = −0.45), and competitor abundance was more important prefire than postfire. When vole abundance was high (prefire), vole dietary niche space was seven times broader than that of deermice. Postfire, deermouse dietary niche nearly tripled and was enriched in 13C (i.e., more C4 plants), while voles occupied a slightly reduced dietary niche (79% of prefire breadth). Our results suggest deermice are experiencing ecological release due to a reduction in vole competition but vole shifts are largely driven by habitat preferences. [ABSTRACT FROM AUTHOR]

Tick control tubes are a host‐targeted tick control method targeting immature Ixodes scapularis ticks attached to mice or found within mouse burrows and nests. Tick control tubes contain permethrin‐treated cotton inside cardboard tubes that mice use as nesting material. Ticks attached to mice or present in their burrows are exposed to the treated cotton. However, there have been variable results using these tubes for tick control. Rodent visitation and use of these tubes may influence their effectiveness. The aim of this study was to evaluate small mammal use of tick control tube cotton and to evaluate whether cotton size or odor attractants changed small mammal tube visitations and cotton removal. For the cotton size experiment, three different cotton sizes were used. In the odor attractant experiment, three different odor attractants were used (peanut butter, safflower oil, and vanillin) along with a commercially available tube as a control. A negative control group that had no cotton present in the tube was used for both experiments. Cotton loss was determined by weighing cotton in deployed tubes weekly, and mouse and nontarget species interactions were evaluated using camera‐trap data collected at each site. While the tested cotton sizes and odor attractants did not affect cotton use, mice did increasingly use cotton during cooler fall months, with the highest use of cotton in October and least use in July. These results suggest that mouse use of cotton was not related to cotton size or odor attractants but was dependent on season. This warrants future research on temporal small mammal use of tick control tubes to determine optimal deployment times for tick control. [ABSTRACT FROM AUTHOR]

Olfactory input into the brain can be disrupted by a variety of environmental factors, including exposure to pathogens or environmental contaminants. Olfactory cues are often eliminated in laboratory rats and mice through highly invasive procedures like olfactory bulbectomy, which may also disrupt accessory olfactory pathways and detection of non‐volatile odors. In the present study, we tested whether inducing anosmia through intranasal infusion of zinc gluconate alters aggression in a monogamous, biparental rodent species, the California mouse (Peromyscus californicus). This less invasive method of manipulating olfaction selectively targets the olfactory epithelium and reduces the detection of volatile odors. Treatment with zinc gluconate extended the time required for male and female California mice to find hidden pieces of apple and reduced the amount of time spent investigating bedding that was soiled by unfamiliar males. Moreover, inhibition of olfaction with zinc gluconate reduced aggressiveness in both sexes as demonstrated by an increased attack latency in the resident‐intruder test among same‐sex dyads from the same treatment group. These results suggest that volatile olfactory cues are necessary for agonistic responses in both male and female California mice. Therefore, even in species with complex social systems that include territorial aggression and monogamy, volatile olfactory cues modulate agonistic behavior. [ABSTRACT FROM AUTHOR]

Per‐ and polyfluoroalkyl substances (PFAS) are compounds manufactured for use in paints, cleaning agents, fire suppressants, nonstick cookware, food containers, and water‐resistant products. Concerns about PFAS stem from their ubiquitous presence in the environment, persistence, and variable/uncertain bioaccumulation and toxicity. In the present study, 5 perfluoroalkyl acids and one polyfluoroalkyl substance were administered to white‐footed mice (Peromyscus leucopus) to elucidate the kinetics of each chemical over 28 d of exposure. Perfluorooctanoate, perfluorohexane sulfonate (PFHxS), and perfluorobutane sulfonate were administered to male and female mice via drinking water. Perfluorooctane sulfonate, perfluorononanoate, 6:2 fluorotelomer sulfonate, and PFHxS were administered to male and female mice via oral gavage. Blood samples collected after 14 or 21 and 28 d of exposure were analyzed for individual PFAS concentrations via liquid chromatography‐tandem mass spectrometry. In general, a plateau in serum concentration in this toxicity test–relevant timeline depended on interactions between 1) the type of PFAS (i.e., perfluoroalkyl sulfonic acids [PFSAs] vs perfluoroalkyl carboxylic acids [PFCAs] vs polyfluorinated), 2) continuous versus bolus dosing, and 3) to a lesser extent, sex. Specifically, PFCAs were detected at higher concentration in females than males, whereas PFSAs were generally detected at similar levels across sex. An exception occurred when PFHxS yielded higher serum levels in males than females through bolus, but not continuous, dosing. Type of PFAS had the largest impact on serum concentrations, whereas sex had the lowest. As such, future work on the toxicokinetics of PFAS in common ecological receptors would be valuable to further explore these patterns. Environ Toxicol Chem 2021;40:2886–2898. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Regional long‐term monitoring can enhance the detection of biodiversity declines associated with climate change, improving future projections by reducing reliance on space‐for‐time substitution and increasing scalability. Rodents are diverse and important consumers in drylands, regions defined by the scarcity of water that cover 45% of Earth's land surface and face increasingly drier and more variable climates. We analyzed abundance data for 22 rodent species across grassland, shrubland, ecotone, and woodland ecosystems in the southwestern USA. Two time series (1995–2006 and 2004–2013) coincided with phases of the Pacific Decadal Oscillation (PDO), which influences drought in southwestern North America. Regionally, rodent species diversity declined 20%–35%, with greater losses during the later time period. Abundance also declined regionally, but only during 2004–2013, with losses of 5% of animals captured. During the first time series (wetter climate), plant productivity outranked climate variables as the best regional predictor of rodent abundance for 70% of taxa, whereas during the second period (drier climate), climate best explained variation in abundance for 60% of taxa. Temporal dynamics in diversity and abundance differed spatially among ecosystems, with the largest declines in woodlands and shrublands of central New Mexico and Colorado. Which species were winners or losers under increasing drought and amplified interannual variability in drought depended on ecosystem type and the phase of the PDO. Fewer taxa were significant winners (18%) than losers (30%) under drought, but the identities of winners and losers differed among ecosystems for 70% of taxa. Our results suggest that the sensitivities of rodent species to climate contributed to regional declines in diversity and abundance during 1995–2013. Whether these changes portend future declines in drought‐sensitive consumers in the southwestern USA will depend on the climate during the next major PDO cycle. [ABSTRACT FROM AUTHOR]

Museum genomics has transformed the field of collections‐based research, opening up a range of new research directions for paleontological specimens as well as natural history specimens collected over the past few centuries. Recent work demonstrates that it is possible to characterize epigenetic markers such as DNA methylation in well preserved ancient tissues. This approach has not yet been tested in traditionally prepared natural history specimens such as dried bones and skins, the most common specimen types in vertebrate collections. In this study, we developed and tested methods to characterize cytosine methylation in dried skulls up to 76 years old. Using a combination of ddRAD and bisulphite treatment, we characterized patterns of cytosine methylation in two species of deer mouse (Peromyscus spp.) collected in the same region in Michigan in 1940, 2003, and 2013–2016. We successfully estimated methylation in specimens of all age groups, although older specimens yielded less data and showed greater interindividual variation in data yield than newer specimens. Global methylation estimates were reduced in the oldest specimens (76 years old) relative to the newest specimens (1–3 years old), which may reflect post‐mortem hydrolytic deamination. Methylation was reduced in promoter regions relative to gene bodies and showed greater bimodality in autosomes relative to female X chromosomes, consistent with expectations for methylation in mammalian somatic cells. Our work demonstrates the utility of historic specimens for methylation analyses, as with genomic analyses; however, studies will need to accommodate the large variance in the quantity of data produced by older specimens. [ABSTRACT FROM AUTHOR]

High‐throughput sequencing technologies are a proposed solution for accessing the molecular data in historical specimens. However, degraded DNA combined with the computational demands of short‐read assemblies has posed significant laboratory and bioinformatics challenges for de novo genome assembly. Linked‐read or "synthetic long‐read" sequencing technologies, such as 10× Genomics, may provide a cost‐effective alternative solution to assemble higher quality de novo genomes from degraded tissue samples. Here, we compare assembly quality (e.g., genome contiguity and completeness, presence of orthogroups) between four new deer mouse (Peromyscus spp.) genomes assembled using linked‐read technology and four published genomes assembled from a single shotgun library. At a similar price‐point, these approaches produce vastly different assemblies, with linked‐read assemblies having overall higher contiguity and completeness, measured by larger N50 values and greater number of genes assembled, respectively. As a proof‐of‐concept, we used annotated genes from the four Peromyscus linked‐read assemblies and eight additional rodent taxa to generate a phylogeny, which reconstructed the expected relationships among species with 100% support. Although not without caveats, our results suggest that linked‐read sequencing approaches are a viable option to build de novo genomes from degraded tissues, which may prove particularly valuable for taxa that are extinct, rare or difficult to collect. [ABSTRACT FROM AUTHOR]

Melanin‐concentrating hormone (MCH) is a conserved neuropeptide, predominantly located in the diencephalon of vertebrates, and associated with a wide range of functions. While functional studies have focused on the use of the traditional mouse laboratory model, critical gaps exist in our understanding of the morphology of the MCH system in this species. Even less is known about the nontraditional animal model Neotomodon alstoni (Mexican volcano mouse). A comparative morphological study among these rodents may, therefore, contribute to a better understanding of the evolution of the MCH peptidergic system. To this end, we employed diverse immunohistochemical protocols to identify key aspects of the MCH system, including its spatial relationship to another neurochemical population of the tuberal hypothalamus, the orexins. Three‐dimensional (3D) reconstructions were also employed to convey a better sense of spatial distribution to these neurons. Our results show that the distribution of MCH neurons in all rodents studied follows a basic plan, but individual characteristics are found for each species, such as the preeminence of a periventricular group only in the rat, the lack of posterior groups in the mouse, and the extensive presence of MCH neurons in the anterior hypothalamic area of Neotomodon. Taken together, these data suggest a strong anatomical substrate for previously described functions of the MCH system, and that particular neurochemical and morphological features may have been determinant to species‐specific phenotypes in rodent evolution. [ABSTRACT FROM AUTHOR]

Speciation is facilitated by "magic traits," where divergent natural selection on such traits also results in assortative mating. In animal populations, diet has the potential to act as a magic trait if populations diverge in consumed food that incidentally affects mating and therefore sexual isolation. While diet‐based assortative mating has been observed in the laboratory and in natural populations, the mechanisms causing positive diet‐based assortment remain largely unknown. Here, we experimentally created divergent diets in a sexually imprinting species of mouse, Peromyscus gossypinus (the cotton mouse), to test the hypothesis that sexual imprinting on diet could be a mechanism that generates rapid and significant sexual isolation. We provided breeding pairs with novel garlic‐ or orange‐flavored water and assessed whether their offspring, exposed to these flavors in utero and in the nest before weaning, later preferred mates that consumed the same flavored water as their parents. While males showed no preference, females preferred males of their parental diet, which is predicted to yield moderate sexual isolation. Thus, our experiment demonstrates the potential for sexual imprinting on dietary cues learned in utero and/or postnatally to facilitate reproductive isolation and potentially speciation. Open Research Badges: This article has earned an Open Data Badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The data is available at https://doi.org/10.5061/dryad.n1qq6v3. [ABSTRACT FROM AUTHOR]

Behaviors that increase an individual's exposure to pathogens are expected to have important effects on immunoactivity. Because sexual reproduction typically requires close contact among conspecifics, mating systems provide an ideal opportunity to study the immunogenetic correlates of behaviors with high versus low risks of pathogen exposure. Despite logical links between polygynandrous mating behavior, increased pathogen exposure, and greater immunoactivity, these relationships have seldom been examined in nonhuman vertebrates. To explore interactions among these variables in a different lineage of mammals, we used RNAseq to study the gene expression profiles of liver tissue—a highly immunoactive organ—from sympatric populations of the monogamous California mouse (Peromyscus californicus) and two polygynandrous congeners (P. maniculatus and P. boylii). Differential expression and co‐expression analyses revealed distinct patterns of gene activity among species, with much of this variation associated with differences in mating system. This tendency was particularly pronounced for MHC genes, with multiple MHC Class I genes being upregulated in the two polygynandrous species, as expected if exposure to sexually transmitted pathogens varies with mating system. Our results underscore the role of mating behavior in influencing patterns of gene expression and highlight the use of emerging transcriptomic tools in behavioral studies of free‐living animals. [ABSTRACT FROM AUTHOR]

Livestock grazing and fire can intensively modify montane meadows. Understanding how these factors affect habitat, species richness, and diversity of small mammals can inform management decisions. Few studies have investigated the independent and synergistic effects of grazing and wildfire on vegetation and small‐mammal communities, and none have focused on montane meadows in the southwestern United States. In 2012 and 2013, we captured small mammals at 105 sites to contrast occupancy, species richness, and diversity among livestock grazing levels (present, absent), wildfire severity (unburned, low, or moderate), and meadow classifications (small or large, wet or dry) in Arizona, USA. During 13,741 trap nights, we captured 1,885 rodents of 8 species. Two species represented 88% of captures: deer mouse (Peromyscus maniculatus) and Arizona montane vole (Microtus montanus arizonensis). Deer mice, Navajo Mogollon voles (Microtus mogollonensis navaho), and thirteen‐lined ground squirrels (Ictidomys tridecemlineatus monticola; a subspecies endemic to the White Mountains, AZ) had higher occupancy in large, ungrazed meadows compared to small, grazed meadows. Species richness was greater in unburned than burned sites and small meadows than large. However, higher diversity occurred in ungrazed and dry compared to grazed and wet meadows. Three species demonstrated weak relationships between wildfire and occupancy, suggesting short‐term (<2 yrs) effects of low to moderate burn severity for these species or their habitat. Livestock grazing had a greater effect than wildfire on the small‐mammal community by altering vegetation or other habitat elements and thus decreasing population sizes. Reducing livestock grazing would benefit small‐mammal species and increase diversity and abundance of the small‐mammal community in montane meadows. © 2019 The Wildlife Society. Livestock grazing negatively affected small‐mammal occupancy and diversity in montane meadows; however, wildfire had little short‐term effect. Grazing altered vegetation or affected habitat elements that decreased population sizes; thus, reducing livestock grazing will benefit small‐mammal species. [ABSTRACT FROM AUTHOR]

Highly variable patterns in temperature and rainfall events can have pronounced consequences for small mammals in resource‐restricted environments. Climatic factors can therefore play a crucial role in determining the fates of small mammal populations. We applied Pradel's temporal symmetry model to a 21‐year capture–recapture dataset to study population dynamics of the pinyon mouse (Peromyscus truei) in a semi‐arid mixed oak woodland in California, USA. We examined time‐, season‐ and sex‐specific variation in realized population growth rate (λ) and its constituent vital rates, apparent survival and recruitment. We also tested the influence of climatic factors on these rates. Overall monthly apparent survival was 0.81 ± 0.004 (estimate ± SE). Survival was generally higher during wetter months (October–May) but varied over time. Monthly recruitment rate was 0.18 ± 0.01, ranging from 0.07 ± 0.01 to 0.63 ± 0.07. Although population growth rate (λ) was highly variable, overall monthly growth rate was close to 1.0, indicating a stable population during the study period (λ ± SE = 0.99 ± 0.01). Average temperature and its variability negatively affected survival, whereas rainfall positively influenced survival and recruitment rates, and thus the population growth rate. Our results suggest that seasonal rainfall and variation in temperature at the local scale, rather than regional climatic patterns, more strongly affected vital rates in this population. Discerning such linkages between species' population dynamics and environmental variability are critical for understanding local and regional impacts of global climate change, and for gauging viability and resilience of populations in resource‐restricted environments. We investigated the effect of intense periods of drought interrupted by extreme rainfall events on a pinyon mouse (Peromyscus truei) population in semi‐arid oak woodland of coastal‐central California. Although pinyon mouse survival and recruitment rates, and therefore growth rates, were highly sensitive to the variations in temperature and rainfall that occurred during the 21 years of study, the population remained stable. It may be fruitful to investigate pinyon mouse population dynamics across the species' broad geographic range, an area increasingly subjected to extreme weather, and intense wildfire. Rowland Willis gives us permission to use the Pinyon Mouse image. [ABSTRACT FROM AUTHOR]

Abstract: When females mate with multiple partners in a reproductive cycle, the relative number of competing sperm from rival males is often the most critical factor in determining paternity. Gamete production is directly related to testis size in most species, and is associated with both mating behavior and perceived risk of competition. Deer mice, Peromyscus maniculatus, are naturally promiscuous and males invest significantly more in sperm production than males of P. polionotus, their monogamous sister‐species. Here, we show that the larger testes in P. maniculatus are retained after decades of enforced monogamy in captivity. While these results suggest that differences in sperm production between species with divergent evolutionary histories can be maintained in captivity, we also show that the early rearing environment of males can strongly influence their testis size as adults. Using a second‐generation hybrid population to increase variation within the population, we show that males reared in litters with more brothers develop larger testes as adults. Importantly, this difference in testis size is also associated with increased fertility. Together, our findings suggest that sperm production may be both broadly shaped by natural selection over evolutionary timescales and also finely tuned during early development. [ABSTRACT FROM AUTHOR]

Abstract: Aim: We examined the effects of chronic hypoxia on diaphragm function in high‐ and low‐altitude populations of Peromyscus mice. Methods: Deer mice (P. maniculatus) native to high altitude and congeneric mice native to low altitude (P. leucopus) were born and raised in captivity to adulthood and were acclimated to normoxia or hypobaric hypoxia (12 or 9 kPa, simulating hypoxia at 4300 and 7000 m) for 6‐8 weeks. We then measured indices of mitochondrial respiration capacity, force production, and fatigue resistance in the diaphragm. Results: Mitochondrial respiratory capacities (assessed using permeabilized fibres with single or multiple inputs to the electron transport system), citrate synthase activity (a marker of mitochondrial volume), twitch force production, and muscle fatigue resistance increased after exposure to chronic hypoxia in both populations. These changes were not well explained by variation in the fibre‐type composition of the muscle. However, there were several differences in diaphragm function in high‐altitude mice compared to low‐altitude mice. Exposure to a deeper level of hypoxia (9 kPa vs 12 kPa) was needed to elicit increases in mitochondrial respiration rates in highlanders. Chronic hypoxia did not increase the emission of reactive oxygen species from permeabilized fibres in highlanders, in contrast to the pronounced increases that occurred in lowlanders. In general, the diaphragm of high‐altitude mice had greater capillary length densities, produced less force in response to stimulation and had shorter relaxation times. The latter was associated with higher activity of sarcoplasmic reticulum Ca2+‐ATPase (SERCA) activity in the diaphragm of high‐altitude mice. Conclusion: Overall, our work suggests that exposure to chronic hypoxia increases the capacities for mitochondrial respiration, force production and fatigue resistance of the diaphragm. However, many of these effects are opposed by evolved changes in diaphragm function in high‐altitude natives, such that highlanders in chronic hypoxia maintain similar diaphragm function to lowlanders in sea level conditions. [ABSTRACT FROM AUTHOR]

Abstract: Host‐associated microbial communities consist of stable and transient members that can assemble through purely stochastic processes associated with the environment or by interactions with the host. Phylosymbiosis predicts that if host–microbiota interactions impact assembly patterns, then one conceivable outcome is concordance between host evolutionary histories (phylogeny) and the ecological similarities in microbial community structures (microbiota dendrogram). This assembly pattern has been demonstrated in several clades of animal hosts in laboratory and natural populations, but in vertebrates, it has only been investigated using samples from faeces or the distal colon. Here, we collected the contents of five gut regions from seven rodent species and inventoried the bacterial communities by sequencing the 16S rRNA gene. We investigated how community structures varied across gut regions and whether the pattern of phylosymbiosis was present along the length of the gut. Gut communities varied by host species and gut region, with Oscillospira and Ruminococcus being more abundant in the stomach and hindgut regions. Gut microbial communities were highly distinguishable by host species across all gut regions, with the strength of the discrimination increasing along the length of the gut. Last, the pattern of phylosymbiosis was found in all five gut regions, as well as faeces. Aspects of the gut environment, such as oxygen levels, production of antimicrobials or other factors, may shift microbial communities across gut regions. However, regardless of these differences, host species maintain distinguishable, phylosymbiotic assemblages of microbes that may have functional impacts for the host. [ABSTRACT FROM AUTHOR]

Abstract: Timing is an essential component of the choices that animals make: The likelihood of successful resource capture (and predator avoidance) depends not just on what an animal chooses to do, but when it chooses to do it. Despite the importance of activity timing, our ability to understand the forces that constrain activity timing has been limited because this aspect of animal behavior is shaped by several factors (e.g., interspecific competitors, predators, physical conditions), and it is difficult to examine activity timing in a setting where only a single factor is operating. Using an island system that makes it possible to focus on the effect of predation risk in the absence of interspecific competition, we examine how the onset of activity of the deer mouse (Peromyscus maniculatus) varies between habitats with unique predation risks (i.e., minimal‐shrub cover versus abundant‐shrub cover sites). Using capture time to assess the timing of mouse activity, we found that mice in habitats with minimal shrub cover were captured 1.7 hr earlier than mice in habitats with abundant shrub cover. This difference in timing between habitats was likely a direct response to differences in predation risk between the two habitats: There were no differences in thermal conditions between the two habitats, and the difference in activity timing disappeared during a night when overcast skies reduced island‐wide predation risk. Our results demonstrate that predation risk, independent of interspecific competition, can generate significant changes in animal activity timing. Our work suggests that habitat structure that provides safety (i.e., refuge habitats) plays a direct role in the timing of prey activity and that habitat modification that alters refuge availability (e.g., shrub dominance) may alter the timing of animal activity. [ABSTRACT FROM AUTHOR]

Aim We compared the control of breathing and heart rate by hypoxia between high- and low-altitude populations of Peromyscus mice, to help elucidate the physiological specializations that help high-altitude natives cope with O2 limitation. Methods Deer mice ( Peromyscus maniculatus) native to high altitude and congeneric mice native to low altitude ( Peromyscus leucopus) were bred in captivity at sea level. The F1 progeny of each population were raised to adulthood and then acclimated to normoxia or hypobaric hypoxia (12 kPa, simulating hypoxia at ~4300 m) for 5 months. Responses to acute hypoxia were then measured during stepwise reductions in inspired O2 fraction. Results Lowlanders exhibited ventilatory acclimatization to hypoxia ( VAH), in which hypoxia acclimation enhanced the hypoxic ventilatory response, made breathing pattern more effective (higher tidal volumes and lower breathing frequencies at a given total ventilation), increased arterial O2 saturation and heart rate during acute hypoxia, augmented respiratory water loss and led to significant growth of the carotid body. In contrast, highlanders did not exhibit VAH - exhibiting a fixed increase in breathing that was similar to hypoxia-acclimated lowlanders - and they maintained even higher arterial O2 saturations in hypoxia. However, the carotid bodies of highlanders were not enlarged by hypoxia acclimation and were similar in size to those of normoxic lowlanders. Highlanders also maintained consistently higher heart rates than lowlanders during acute hypoxia. Conclusions Our results suggest that highland deer mice have evolved high rates of alveolar ventilation and respiratory O2 uptake without the significant enlargement of the carotid bodies that is typical of VAH in lowlanders, possibly to adjust the hypoxic chemoreflex for life in high-altitude hypoxia. [ABSTRACT FROM AUTHOR]

Aim We surveyed the genetic variability of deermice (genus Peromyscus) at the north-western edge of their range to test for occupancy in multiple, hypothesized ice-free regions during the late Pleistocene and explore post-glacial dynamics. Location North-western North America. Methods We used sequences from four independent nuclear and mitochondrial loci from 341 specimens of Peromyscus maniculatus, Peromyscus keeni and Peromyscus sp. (Yukon) to assess species limits, population structure, and demographical change as a result of historical climate change, using a Bayesian approach. Species distribution models were built in MaxEnt to explore the niche overlap amongst genetically distinct species. Results Divergence amongst three lineages began before the last interglacial, and each shows signs of post-glacial expansion. Multilocus species trees strongly support P. keeni and Peromyscus sp. (Yukon) as independent from P. maniculatus. Substantial substructure was observed for P. keeni across the fragmented Alexander Archipelago. Northern lineages or clades ( Peromyscus sp. and P. keeni) differed in potential ecological distributions. Main conclusions At the extreme north-western range of deermice in North America, three distinct lineages persist reflecting divergence in at least three ice-free regions [Beringia, Coastal (near Southeast Alaska) and Southern Continental] throughout the latest Pleistocene glacial cycles. Although spatially proximate in Yukon, no locations were identified where these lineages are in contact. Further, west along the Pacific Coast, P. keeni is widespread across the complex landscape of Southeast Alaska, yet there is limited contemporary gene flow amongst island populations, a finding consistent with the barriers produced by rising sea levels at the end of the Last Glacial Maximum. [ABSTRACT FROM AUTHOR]

The Key Largo woodrat ( Neotoma floridana smalli) and Key Largo cotton mouse ( Peromyscus gossypinus allapaticola) are federally endangered subspecies endemic to the tropical hardwood hammocks of Key Largo, Florida. Woodrats are considered generalists in habitat and diet, yet a steady decline in natural stick nests and capture rates over the past several decades suggests that they are limited by the availability of nesting habitat due to habitat loss and fragmentation. The more specialized Key Largo cotton mouse appears to rely on old growth hammock, a habitat type that is rare following past land clearing. In 2004, the U.S. Fish and Wildlife Service started building supplemental nest structures to restore habitat quality and connectivity for these endangered rodents, but nest use requires evaluation. We used camera traps and occupancy models to evaluate the factors influencing woodrat and cotton mouse use of the supplemental nests. We detected woodrats at 65 and cotton mice at 175 of 284 sampled nest structures, with co-occurrence at 38 nests. Woodrat nest use followed a gradient from low nest use in the north to high nest use in the south, which might relate to the proximity of free-ranging domestic cat ( Felis catus) colonies in residential developments. Cotton mouse nest use, however, was related positively to mature hammock and related negatively to disturbed areas (e.g. scarified lands). The two species occurred independently of each other. Stick-stacking behavior was observed at supplemental nests and, although it was correlated with detection of woodrats, it was not a strong predictor of their occurrence. We suggest that nest supplementation can be an important tool for species recovery as habitat quality continues to improve with succession. [ABSTRACT FROM AUTHOR]

A central goal of evolutionary biology is to understand the molecular mechanisms underlying phenotypic adaptation. While the contribution of protein-coding and cis-regulatory mutations to adaptive traits has been well documented, additional sources of variation - such as the production of alternative RNA transcripts from a single gene, or isoforms - have been understudied. Here, we focus on the pigmentation gene Agouti, known to express multiple alternative transcripts, to investigate the role of isoform usage in the evolution of cryptic colour phenotypes in deer mice (genus Peromyscus). We first characterize the Agouti isoforms expressed in the Peromyscus skin and find two novel isoforms not previously identified in Mus. Next, we show that a locally adapted light-coloured population of P. maniculatus living on the Nebraska Sand Hills shows an upregulation of a single Agouti isoform, termed 1C, compared with their ancestral dark-coloured conspecifics. Using in vitro assays, we show that this preference for isoform 1C may be driven by isoform-specific differences in translation. In addition, using an admixed population of wild-caught mice, we find that variation in overall Agouti expression maps to a region near exon 1C, which also has patterns of nucleotide variation consistent with strong positive selection. Finally, we show that the independent evolution of cryptic light pigmentation in a different species, P. polionotus, has been driven by a preference for the same Agouti isoform. Together, these findings present an example of the role of alternative transcript processing in adaptation and demonstrate molecular convergence at the level of isoform regulation. [ABSTRACT FROM AUTHOR]

Apex predators can suppress the foraging activity of mesopredators, which may then result in cascading benefits for the prey of those mesopredators. We studied the interactions between a top predator, the Barn Owl ( Tyto alba), and their primary prey, an island endemic deer mouse ( Peromyscus maniculatus elusus), which in turn consumes the eggs of seabirds nesting on Santa Barbara Island in California. Scripps's Murrelets ( Synthliboramphus scrippsi), a threatened nocturnal seabird, arrive annually to breed on this island, and whose first egg is particularly vulnerable to predation by mice. We took advantage of naturally occurring extreme variations in the density of mice and owls on the island over 3 years and predicted that (1) mouse foraging would decrease with increasing predation risk from owls and moonlight and (2) these decreases in foraging would reduce predation on murrelet eggs. We measured the giving up densities of mice with experimental foraging stations and found that mice were sensitive to predation risk and foraged less when owls were more abundant and less during the full moon compared to the new moon. We also monitored the fates of 151 murrelet eggs, and found that murrelet egg predation declined as owl abundance increased, and was lower during the full moon compared to the new moon. Moreover, high owl abundance suppressed egg predation even when mice were extremely abundant. We conclude that there is a behaviorally mediated cascade such that owls on the island had a positive indirect effect on murrelet egg survival. Our study adds to the wider recognition of the strength of risk effects to structure food webs, as well as highlighting the complex ways that marine and terrestrial food webs can intersect. [ABSTRACT FROM AUTHOR]

Food webs composed of similar consumers can vary based on nutrient input, habitat structure, and other factors. For wetland-associated species, fluctuating water levels can potentially affect habitat quality, which in turn can affect trophic diversity. Our objective was to determine spatiotemporal variation in the trophic structure of small mammals at two wetland complexes (floodplain and mineland) in southern Illinois. We live-trapped small mammals during 2011-2013 at nine wetland patches on the Mississippi River floodplain and 14 patches at a reclaimed mineland. We collected hair samples from six species of small mammals (n = 428) at these wetland complexes. We analyzed C and N stable isotopes for three mammal taxa (Oryzomys palustris, Peromyscus spp., Microtus ochrogaster) to compare diet between species, sites, and times. Food sources (vegetation and invertebrates) were collected to form the isotopic baseline. We found no seasonal difference in diet composition, but isotopic values varied between sites and species. At the floodplain site, both δ15N and δ13C isotopic values for Oryzomys were more variable and completely enclosed that of Peromyscus. At the mining site, Peromyscus were at a lower trophic level (δ15N) and had a separate and less variable δ13C values from Oryzomys. Microtus was at a lower trophic position than the other two species at both sites. These results point to reduced niche overlap between Oryzomys and Peromyscus at the mining site, perhaps due to lower habitat quality and limited suitable resources. At the floodplain site, we conclude that more dynamic hydrology gave rise to higher biodiversity and more resources allowing small mammals to use similar food items. [ABSTRACT FROM AUTHOR]

For small mammals living at high altitude, aerobic heat generation (thermogenesis) is essential for survival during prolonged periods of cold, but is severely impaired under conditions of hypobaric hypoxia. Recent studies in deer mice ( Peromyscus maniculatus) reveal adaptive enhancement of thermogenesis in high- compared to low-altitude populations under hypoxic cold stress, an enhancement that is attributable to modifications in the aerobic metabolism of muscles used in shivering. However, because small mammals rely heavily on nonshivering mechanisms for cold acclimatization, we tested for evidence of adaptive divergence in nonshivering thermogenesis ( NST) under hypoxia. To do so, we measured NST and characterized transcriptional profiles of brown adipose tissue ( BAT) in high- and low-altitude deer mice that were (i) wild-caught and acclimatized to their native altitude, and (ii) born and reared under common garden conditions at low elevation. We found that NST performance under hypoxia is enhanced in wild-caught, high-altitude deer mice, a difference that is associated with increased expression of coregulated genes that influence several physiological traits. These traits include vascularization and O2 supply to BAT, brown adipocyte proliferation and the uncoupling of oxidative phosphorylation from ATP synthesis in the generation of heat. Our results suggest that acclimatization to hypoxic cold stress is facilitated by enhancement of nonshivering heat production, which is driven by regulatory plasticity in a suite of genes that influence intersecting physiological pathways. [ABSTRACT FROM AUTHOR]

Urbanization results in pervasive habitat fragmentation and reduces standing genetic variation through bottlenecks and drift. Loss of genomewide variation may ultimately reduce the evolutionary potential of animal populations experiencing rapidly changing conditions. In this study, we examined genomewide variation among 23 white-footed mouse (Peromyscus leucopus) populations sampled along an urbanization gradient in the New York City metropolitan area. Genomewide variation was estimated as a proxy for evolutionary potential using more than 10 000 single nucleotide polymorphism (SNP) markers generated by ddRAD-Seq. We found that genomewide variation is inversely related to urbanization as measured by percent impervious surface cover, and to a lesser extent, human population density. We also report that urbanization results in enhanced genomewide differentiation between populations in cities. There was no pattern of isolation by distance among these populations, but an isolation by resistance model based on impervious surface significantly explained patterns of genetic differentiation. Isolation by environment modeling also indicated that urban populations deviate much more strongly from global allele frequencies than suburban or rural populations. This study is the first to examine loss of genomewide SNP variation along an urban-to-rural gradient and quantify urbanization as a driver of population genomic patterns. [ABSTRACT FROM AUTHOR]

Predicting outbreaks of zoonotic infections in reservoir hosts that live in highly fluctuating environments, such as Sin Nombre virus (SNV) in deer mice, is particularly challenging because host populations vary widely in response to environmental conditions and the relationship between field infection rates and abundance often appears to contradict conventional theory. Using a stage-structured host-pathogen model parameterized and crossvalidated from a unique 15-year data set, we show how stochastic population fluctuations can lead to predictable dynamics of SNV in deer mice. Significant variation in host abundance and the basic reproductive number of the virus results in intermittent crossing of the critical host population density necessary for SNV endemicity and frequent local extinctions. When environmental conditions favor growth of the host population above the threshold, host- pathogen interactions lead to delayed density dependence in reservoir prevalence. The resultant ecological delay may provide a neglected opportunity for outbreak prediction in zoonoses. [ABSTRACT FROM AUTHOR]

High-throughput sequencing is revealing that most macro-organisms house diverse microbial communities. Of particular interest are disease vectors whose microbiome could potentially affect pathogen transmission and vector competence. We investigated bacterial community composition and diversity of the ticks Dermacentor variabilis ( n = 68) and Ixodes scapularis ( n = 15) and blood of their shared rodent host, Peromyscus leucopus ( n = 45) to quantify bacterial diversity and concordance. The 16S rRNA gene was amplified from genomic DNA from field-collected tick and rodent blood samples, and 454 pyrosequencing was used to elucidate their bacterial communities. After quality control, over 300 000 sequences were obtained and classified into 118 operational taxonomic units ( OTUs, clustered at 97% similarity). Analysis of rarefied communities revealed that the most abundant OTUs were tick species-specific endosymbionts, Francisella and Rickettsia, and the commonly flea-associated bacterium Bartonella in rodent blood. An Arsenophonus and additional Francisella endosymbiont were also present in D. variabilis samples. Rickettsia was found in both tick species but not in rodent blood, suggesting that it is not transmitted during feeding. Bartonella was present in larvae and nymphs of both tick species, even those scored as unengorged. Relatively, few OTUs (e.g. Bartonella, Lactobacillus) were found in all sample types. Overall, bacterial communities from each sample type were significantly different and highly structured, independent of their dominant OTUs. Our results point to complex microbial assemblages inhabiting ticks and host blood including infectious agents, tick-specific endosymbionts and environmental bacteria that could potentially affect arthropod-vectored disease dynamics. [ABSTRACT FROM AUTHOR]

Genomic resources are important and attainable for examining evolutionary change in divergent natural populations of nonmodel species. We utilized two next-generation sequencing ( NGS) platforms, 454 and SOLi D 5500 XL, to assemble low-coverage transcriptomes of the white-footed mouse ( Peromyscus leucopus), a widespread and abundant native rodent in eastern North America. We sequenced liver m RNA transcripts from multiple individuals collected from urban populations in New York City and rural populations in undisturbed protected areas nearby and assembled a reference transcriptome using 1 080 065 954 SOLi D 5500 XL (75 bp) reads and 3 052 640 454 GS FLX + reads. The reference contained 40 908 contigs with a N50 = 1044 bp and a total content of 30.06 Megabases ( Mb). Contigs were annotated from Mus musculus (39.96% annotated) Uniprot databases. We identified 104 655 high-quality single nucleotide polymorphisms ( SNPs) and 65 single sequence repeats ( SSRs) with flanking primers. We also used normalized read counts to identify putative gene expression differences in 10 genes between populations. There were 19 contigs significantly differentially expressed in urban populations compared to rural populations, with gene function annotations generally related to the translation and modification of proteins and those involved in immune responses. The individual transcriptomes generated in this study will be used to investigate evolutionary responses to urbanization. The reference transcriptome provides a valuable resource for the scientific community using North American Peromyscus species as emerging model systems for ecological genetics and adaptation. [ABSTRACT FROM AUTHOR]

Parasite transmission is determined by the rate of contact between a susceptible host and an infective stage and susceptibility to infection given an exposure event. Attempts to measure levels of variation in exposure in natural populations can be especially challenging. The level of exposure to a major class of parasites, trophically transmitted parasites, can be estimated by investigating the host's feeding behaviour. Since the parasites rely on the ingestion of infective intermediate hosts for transmission, the potential for exposure to infection is inherently linked to the definitive host's feeding ecology. Here, we combined epidemiological data and molecular analyses (polymerase chain reaction) of the diet of the definitive host, the white-footed mouse ( Peromyscus leucopus), to investigate temporal and individual heterogeneities in exposure to infection. Our results show that the consumption of cricket intermediate hosts accounted for much of the variation in infection; mice that had consumed crickets were four times more likely to become infected than animals that tested negative for cricket DNA. In particular, pregnant female hosts were three times more likely to consume crickets, which corresponded to a threefold increase in infection compared with nonpregnant females. Interestingly, males in breeding condition had a higher rate of infection even though breeding males were just as likely to test positive for cricket consumption as nonbreeding males. These results suggest that while heterogeneity in host diet served as a strong predictor of exposure risk, differential susceptibility to infection may also play a key role, particularly among male hosts. By combining PCR analyses with epidemiological data, we revealed temporal variation in exposure through prey consumption and identified potentially important individual heterogeneities in parasite transmission. [ABSTRACT FROM AUTHOR]

The Anacapa deer mouse is an endemic subspecies that inhabits Anacapa Island, part of Channel Islands National Park, California. We used mitochondrial DNA cytochrome c oxidase subunit II gene ( COII) and 10 microsatellite loci to evaluate the levels of genetic differentiation and variation in ∼1400 Anacapa deer mice sampled before and for 4 years after a black rat ( Rattus rattus) eradication campaign that included trapping, captive holding and reintroduction of deer mice. Both mitochondrial and microsatellite analyses indicated significant differentiation between Anacapa deer mice and mainland mice, and genetic variability of mainland mice was significantly higher than Anacapa mice even prior to reintroduction. Bayesian cluster analysis and Principal Coordinates Analysis indicated that East, Middle and West Anacapa mice were genetically differentiated from each other, but translocation of mice among islands resulted in the East population becoming less distinct as a result of management. Levels of heterozygosity were similar before and after management. However, numerous private alleles in the founder populations were not observed after reintroduction and shifts in allele frequencies occurred, indicating that the reintroduced populations experienced substantial genetic drift. Surprisingly, two mitochondrial haplotypes observed in an earlier study of Anacapa deer mice were lost in the 20 years prior to the rat eradication program, leaving only a single haplotype in Anacapa deer mice. This study demonstrates how genetic monitoring can help to understand the re-establishment of endemic species after the eradication of invasive species and to evaluate the effectiveness of the management strategies employed. [ABSTRACT FROM AUTHOR]

Sin Nombre virus (SNV), a strain of hantavirus, causes hantavirus pulmonary syndrome (HPS) in humans, a deadly disease with high mortality rate (> 50%). The primary virus host is the deer mouse, and greater abundance of deer mice has been shown to increase the human risk of HPS. Our aim is to identify and compare vegetation indices and associated time lags for predicting hantavirus risk using remotely sensed imagery. Utah, USA. A 5-year time-series of moderate-resolution imaging spectroradiometer (MODIS) satellite imagery and corresponding field data was utilized to compare various vegetation indices that measure productivity with the goal of indirectly estimating mouse abundance and SNV prevalence. Relationships between the vegetation indices and deer mouse density, SNV prevalence and the number of infected deer mice at various time lags were examined to assess which indices and associated time lags might be valuable in predicting SNV outbreaks. The results reveal varying levels of positive correlation between the vegetation indices and deer mouse density as well as the number of infected deer mice. Among the vegetation indices, the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI) produced the highest correlations with deer mouse density and the number of infected deer mice using a time lag of 1.0 to 1.3 years for May and June imagery. This study demonstrates the potential for using MODIS time-series satellite imagery in estimating deer mouse abundance and predicting hantavirus risk. The 1-year time lag provides a great opportunity to apply satellite imagery to predict upcoming SNV outbreaks, allowing preventive strategies to be adopted. Analysis of different predictive indices and lags could also be valuable in identifying the time windows for data collection for practical uses in monitoring rodent abundance and subsequent disease risk to humans. [ABSTRACT FROM AUTHOR]

Abstract: Restricted repetitive behaviors (stereotypy, compulsions, rituals) are diagnostic for autism spectrum disorder and common in related neurodevelopmental disorders. Despite their prevalence in clinical populations, underlying mechanisms associated with the development of these behaviors remain poorly understood. We examined the role of the indirect basal ganglia pathway in the development of stereotypy using deer mice. We measured neuronal metabolic activity in the subthalamic nucleus (STN) and other relevant brain regions using cytochrome oxidase (CO) histochemistry at three developmental time-points. Although no differences were observed in STN across development, significant differences were found when mice were grouped by developmental trajectory. At 6 weeks post-weaning, significantly lower CO activity in STN was found in those trajectory groups that developed high levels of repetitive behavior versus the trajectory group that did not, suggesting the development of stereotypy is associated with decreased indirect basal ganglia pathway activity. In addition, we tested the hypothesis that preferential activation of striatal striosomes relative to surrounding matrix would be associated with the development of stereotypy. No differences in the relative activation of these striatal compartments were observed across development or among trajectory groups. Our results point to dynamic changes in the indirect pathway associated with the development of repetitive behavior and extends our prior work linking reduced indirect pathway activation to stereotypy in adult deer mice. [Copyright &y& Elsevier]

Pathogens and immune challenges can induce changes in host phenotype in ways that indirectly impact important community interactions, including those that affect host-pathogen interactions. To explore host behavioural response to immune challenge, we exposed wild white-footed mice ( Peromyscus leucopus) to an immunogen from an endemic, zoonotic pathogen, the spirochete Borrelia burgdorferi. White-footed mice are a major reservoir host of Lyme disease (LD) spirochetes in northeastern USA and an abundant member of forest communities. The activity patterns, foraging behaviour, and space use of white-footed mice have implications for population growth rates of community members upon which mice incidentally prey (i.e. gypsy moths and native thrushes), as well as potentially determining host-vector encounter rates and human risk of LD. Immunochallenge led to specific humoral (antibody) and cellular (i.e. elevated neutrophils and eosinophils) immune responses, supporting use of the immunogen as a surrogate for pathogenic infection. Immunochallenged mice had reduced wheel-running activity early in the night when measured in the lab. However, mouse activity, as measured by track plates in natural field experiments, did not differ between mice exposed to the immunogen and unexposed mice. Foraging behaviour of wild mice in the field - assessed with giving-up densities of seed at artificial feeding stations - was affected by exposure to the immunogen. Whereas immunochallenge did not influence whether foraging mice gained information on patch quality while foraging, it led to reductions in predator avoidance during foraging, suggesting that the proportion of space used by foraging mice may be greater as a result of immunochallenge. This increased space use is predicted to increase encounter rates with patchily distributed LD vectors (ticks) and with incidental prey items. Thus, immunochallenge in white-footed mice, and potentially pathogenic infection, have the potential to indirectly impact community interactions, including those important for pathogen transmission. [ABSTRACT FROM AUTHOR]

Heavy metal contamination negatively affects natural systems including plants, birds, fish and bacteria by reducing biodiversity at contaminated sites. At the Tri-State Mining District, efforts have been made to remediate sites to mitigate the detrimental effects that contamination has caused on human health. While the remediation effort has returned the site to within federal safety standards, it is unclear if this effort is sufficient to restore floral and faunal communities. Intrinsic to ecosystem and organism health is the biodiversity and composition of microbial communities. We have taken advantage of recent advances in sequencing technology and surveyed the bacterial community of remediated and reference soils as well as the intestinal microbial community of two ubiquitous rodent species to provide insight on the impacts of residual heavy metal contamination on the ecosystem. Rodents found on the remediated site had reduced body mass, smaller body size and lower body fat than animals on reference sites. Using bar-coded, massively parallel sequencing, we found that bacterial communities in both the soil and Peromyscus spp. gastrointestinal tracts had no difference in diversity between reference and remediated sites but assemblages differed in response to contamination. These results suggest that niche voids left by microbial taxa that were unable to deal with the remnant levels of heavy metals on remediated sites were replaced by taxa that could persist in this environment. Whether this replacement provided similar ecosystem services as ancestral bacterial communities is unknown. [ABSTRACT FROM AUTHOR]

Climate change, human disturbance, and disease can have large impacts on the dynamics of a species by affecting the likelihood of survival and reproduction of individuals. We investigated the roles of precipitation, off-road vehicle (ORV) alteration of habitat, and infection with Sin Nombre virus on the survival and reproductive probabilities of deer mice (Peromyscus maniculatus). We used generalized linear mixed models to estimate the effects of these factors and their interactions by fitting capture-recapture data collected seasonally from 2002 to 2007 at 17 sites in the Great Basin Desert of central Utah, USA. During periods with high precipitation, we found no difference in survival and reproductive probabilities between seasons, but during drier periods, we found a reduction of overwinter survival and fall reproductive activity. Precipitation also interacted with disturbance to affect survival probabilities and female reproduction; in periods With low precipitation, deer mice on highly disturbed sites had extremely low survival probabilities and low reproductive probabilities of females compared to those of individuals from low-disturbance sites. However, high precipitation ameliorated the effect of disturbance on both parameters. Deer mice from sites with high impact of ORV disturbance also had low survival over summer. Additionally, male reproductive probabilities were diminished on highly disturbed sites in both seasons; in contrast, they were reduced only in the fall on low-disturbance sites. Density had an overall negative effect on survival and reproductive probabilities of deer mice. For females, the negative effect on reproductive activity was amplified in highly disturbed sites. We found no effect of hantavirus infection on survival probabilities of deer mice. Overall, this study revealed complexity in the determinants of deer mouse survival and reproduction given by the effects of a number of significant interactions among explanatory variables. Thus, factors that may not appear to have a strong effect when investigated alone can still be influential by modulating the effect of a different factor. [ABSTRACT FROM AUTHOR]

1. Understanding the links between physiological performance and fitness is key to predicting the responses of individuals to environmental change, especially that imposed by climate. Of particular interest are traits linked with metabolic performance. In particular, maximal metabolic rate (MMR; which describes the upper limit to heat production) and basal metabolic rate (BMR; which describes the lower limit to heat production for a normothermic endotherm) are important causal mechanisms that determine the physiological limits for activity under cold conditions. 2. Previous work with deer mice has shown important links between maximal metabolic performance and activity. Selection for elevated MMRs was detected in nature, and higher rates of above-ground activity during periods of cold were associated with elevated MMRs. Here, we investigate further the links between activity and elevated MMRs. 3. We conducted a laboratory study to test whether BMR or MMR was correlated with activity and foraging behaviour of deer mice exposed to a series of cold temperatures (–5, –10 and –15 °C). Each mouse had access to a warm nest box, but needed to enter a cold environmental chamber to access food, ice chips and a running wheel. Behaviours were monitored for 2 days under these experimental conditions. Prior to the experimental trials, BMR and MMR were measured. MMR was also measured after the trials. 4. The amount of time that mice spent active in the cold was negatively correlated with ambient temperature. The duration of activity per bout (when mice were out of the nest box) decreased at colder temperatures, but the number of bouts did not. The total duration of activity and duration per bout increased with an individual's MMR and change in MMR over the course of the experiment. Body mass decreased at colder temperatures, and mice with higher MMR and greater increases in MMR consumed more food. 5. Our study suggests that mice with high MMR, or a capacity to increase MMR may be best able to tolerate cold environments. Thus, physiological capacity and behaviour can influence each other in response to environmental conditions. 6. Integrative studies between behaviour and physiology in an ecological context provide greater understanding of the potential responses of organisms to environmental change. With respect to climate, such responses will depend either on the ability of individuals to induce plastic (or acclamatory) responses to environmental stressors or on the structure of genetic variation for physiological traits within a particular population. Although, some effort has been directed at understanding the evolutionary significance of metabolic traits (particularly with respect to heritabilities), we suggest that priority should be given to studies that explicitly address the mechanistic links between physiology and fitness in light of ongoing climate change. [ABSTRACT FROM AUTHOR]

The risk of arsenic exposure to deer mice (Peromyscus maniculatus) living in areas of naturally and anthropogenically elevated arsenic levels was determined using three separate calculations of arsenic daily intake: Estimated daily intake (EDI), bioaccessible EDI (BEDI), and actual daily intake (ADI). The present work is of particular interest, because the risk assessments were determined for animals naturally exposed to arsenic. Gastric fluid extraction was used to obtain bioaccessibility data for soil and plant samples collected from three study sites (background, mine forest, and tailings) in Yellowknife (NT, Canada). Calculations using the EDI indicated that deer mice living in tailings habitat (average soil arsenic concentration, 1,740 ± 2,240 μg/g) should have been experiencing serious health effects as a result of their exposure to arsenic. Using BEDI and ADI in the risk assessment calculation, however, resulted in an order-of-magnitude decrease in calculated risk. In addition, results calculated using the BEDI and ADI were not significantly different, suggesting that using bioaccessibility provides a more realistic estimate of potential risk. The present results provide evidence that the use of EDI in traditional risk assessments may seriously overestimate the actual risk, which in some instances may result in expensive and unnecessary clean-up measures. [ABSTRACT FROM AUTHOR]

Oestrogen receptor (ER)α immunoreactivity in three brain regions relevant to maternal behaviour (medial preoptic area, bed nucleus of the stria terminalis and medial amygdala) was measured in two species of dwarf hamster that both mate during a postpartum oestrous but differ in expression of paternal behaviour. Male and female Phodopus campbelli and Phodopus sungorus were sampled as sexually naïve adults, following mating to satiety, and as new parents. In all brain regions, females expressed higher levels of ERα than males. Species did not have an effect on ERα distribution except in the medial amygdala, where P. sungorus females had higher expression levels than all other groups. Behavioural status was not associated with altered ERα expression. These results were not expected for females and suggest that a primary activational role for oestrogen, acting through ERα in these regions, does not generalise to maternal behaviour in Phodopus. In males, these results are consistent with previous manipulations of the ERα ligand, oestrogen, and suggest that paternal behaviour in P. campbelli is likely to be regulated by developmental effects of oestrogen on the brain during early life (similar to Microtus ochrogaster), rather than through activation by oestrogen at the time of fatherhood (similar to Peromyscus californicus). [ABSTRACT FROM AUTHOR]

Blood meals by blacklegged ticks (Ixodes scapularis) on vertebrate hosts serve to transmit the agents of several zoonotic diseases, including Lyme disease, human babesiosis, and human granulocytic anaplasmosis, between host and tick. If ticks are aggregated on hosts, a small proportion of hosts may be responsible for most transmission events. Therefore, a key element in understanding and controlling the transmission of these pathogens is identifying the group(s) or individuals feeding a disproportionate number of ticks. Previous studies of tick burdens, however, have focused on differences in mean annual burdens between one or a few groups of hosts, ignoring both the strong seasonal dynamics of I. scapularis and their aggregation on hosts. We present a statistical modeling framework that predicts burdens on individual hosts throughout the year as a function of temporal-, site-, and individual-specific attributes, as well as the degree of aggregation in a negative binomial distribution. We then fit alternate versions of this model to an II-year data set off. scapularis burdens on white-footed mice (Perornyscus leucopus) and eastern chipmunks (Tainias striatus) to explore which factors are important to predicting tick burdens. We found that tick burdens are a complex function of many extrinsic and intrinsic factors, including seasonality. Specifically: (1) burdens on mice and chipmunks increased with densities of host-seeking ticks in a manner that suggests hosts become saturated. (2) Chipmunks draw larval ticks away from mice, which are efficient reservoirs of the Lyme disease bacterium, and mice draw nymphs away from chipmunks, which are key nymphal hosts. (3) While individual correlates were statistically important, the relationships were complex, and no group or correlate (sex, age, mass) could explain which hosts fed a disproportionate number of ticks. (4) Ticks were strongly aggregated on hosts within and across groups suggesting that some undiscovered quality of individual hosts was responsible for the aggregation. (5) Those individuals that fed more nymphs than expected, and are thus more likely to be infected with the Lyme disease agent, also tend to feed and infect more larvae than expected. Predicting which individuals those are is not yet possible. [ABSTRACT FROM AUTHOR]

1. Species invasions are a primary driver of species additions and deletions in ecosystems. Understanding the intricacies of invasions and their consequences is central to ecology and biodiversity conservation. Extinctions are rarely random and often are influenced by a suite of factors. 2. We explored abiotic and biotic factors that correlate with and help to provide proximate explanations for insular extinctions driven by invasive predators on islands off western Mexico. 3. A number of factors that were hypothesized a priori to explain the observed extinction patterns performed better than island size alone. Alternative prey available to invasive predators was negatively correlated with extinction, with twice the number of alternative prey species present on extinction-free islands compared to islands with extinctions. Carrying capacity estimates of extant populations were 27 times that of extinct populations. 4. An aggregate model that included alternative prey, carrying capacity, and seasonal precipitation was the best performing model. Those factors, which are supported by theory and empirical evidence, are informative to conservation decision-makers. 5. Synthesis and applications. Islands with small native mammals and no, or few, alternative prey species available to invasive predators should be prioritized for eradication. By focusing regionally on a specific threat, we provide a framework to practitioners that aids in prioritizing invasive predator eradications to halt insular extinctions. [ABSTRACT FROM AUTHOR]

The heterogeneity of catchability (HC) among the individuals encountered during a capture–recapture study has long been regarded as a liability. However, heterogeneous capture probabilities may reflect interesting but hidden features of the population, such as social status. The difficulty is to distinguish between this intrinsic heterogeneity and the extrinsic heterogeneity induced by the study itself. So far, population ecologists have not been able to distinguish between these two sources of variation in capture heterogeneity because, in the presence of heterogeneity of capture in the data, they have frequently used a too simple approach. This traditional approach, which consists of incorporating two common sources of lack of fit (transience and trap-dependence), does not directly model the HC and thus cannot investigate its biological meaning. In this context, we propose, for open populations, to directly model the HC by employing multievent models. Multievent models make it possible to break HC into two classes of catchability viewed as uncertain states. With the introduction of a coefficient of heterogeneity to model proportional probabilities of capture over time in the two classes, our approach allows the investigation of HC in a parsimonious way. In this paper, we apply both this new approach and the traditional approach to a long-term data set of male deer mice Peromyscus maniculatus. We then compare 13 candidate models separately for each approach. Our results indicate that the new approach is superior to the traditional approach. [ABSTRACT FROM AUTHOR]

In a variety of animal taxa, proteins involved in reproduction evolve more rapidly than nonreproductive proteins. Most studies of reproductive protein evolution, however, focus on divergence between species, and little is known about differentiation among populations within a species. Here we investigate the molecular population genetics of the protein ZP3 within two Peromyscus species. ZP3 is an egg coat protein involved in primary binding of egg and sperm and is essential for fertilization. We find that amino acid polymorphism in the sperm-combining region of ZP3 is high relative to silent polymorphism in both species of Peromyscus. In addition, while there is geographical structure at a mitochondrial gene ( Cytb), a nuclear gene ( Lcat) and eight microsatellite loci, we find no evidence for geographical structure at Zp3 in Peromyscus truei. These patterns are consistent with the maintenance of ZP3 alleles by balancing selection, possibly due to sexual conflict or pathogen resistance. However, we do not find evidence that reinforcement promotes ZP3 diversification; allelic variation in P. truei is similar among populations, including populations allopatric and sympatric with sibling species. In fact, most alleles are present in all populations sampled across P. truei's range. While additional data are needed to identify the precise evolutionary forces responsible for sequence variation in ZP3, our results suggest that in Peromyscus, selection to maintain divergent alleles within species contributes to the pattern of rapid amino acid substitution observed among species. [ABSTRACT FROM AUTHOR]