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A critical time in the life of a male occurs at reproduction, when his behaviour, physiology and resources must be brought to bear for the central purpose of his life-propagating his genes. We ask whether reproduction results in dysfunction of the stress axis, is linked to life history, and causes senescence. We assessed if deterioration in the axis underlies variation in reproductive lifespan in males of five species of North American ground squirrels whose life history varies from near semelparity to iteroparity. The most stressful and energy-demanding time occurs in spring during the intense 2-3 week breeding competition just after arousal from hibernation. We compared their stress axis functioning before and after the mating period using a hormonal challenge protocol. We found no evidence of stress axis dysfunction after reproduction in any species nor was there a relationship between reproductive lifespan and stress axis functional deterioration. Moreover, there was no consistent relationship between free cortisol levels and downstream measures (energy mobilization, haematology, immunity and body indices of condition). Thus, stress axis function was not traded off to promote reproduction irrespective of life history and lifespan, and we conclude that it is a prerequisite for life. Hence, it functions as a constraint and does not undergo senescence.

Long-term monitoring is critical to determine the stability and sustainability of wildlife populations, and if change has occurred, why. We have followed population density changes in the small mammal community in the boreal forest of the southern Yukon for 46 years with density estimates by live trapping on 3-5 unmanipulated grids in spring and autumn. This community consists of 10 species and was responsible for 9% of the energy flow in the herbivore component of this ecosystem from 1986 to 1996, but this increased to 38% from 2003 to 2014. Small mammals, although small in size, are large in the transfer of energy from plants to predators and decomposers. Four species form the bulk of the biomass. There was a shift in the dominant species from the 1970s to the 2000s, with Myodes rutilus increasing in relative abundance by 22% and Peromyscus maniculatus decreasing by 22%. From 2007 to 2018, Myodes comprised 63% of the catch, Peromyscus 20%, and Microtus species 17%. Possible causes of these changes involve climate change, which is increasing primary production in this boreal forest, and an associated increase in the abundance of 3 rodent predators, marten (Martes americana), ermine (Mustela ermine) and coyotes (Canis latrans). Following and understanding these and potential future changes will require long-term monitoring studies on a large scale to measure metapopulation dynamics. The small mammal community in northern Canada is being affected by climate change and cannot remain stable. Changes will be critically dependent on food-web interactions that are species-specific., (© 2019 The Authors. Integrative Zoology published by International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.)

Pregnancy is one of the defining characteristics of placental mammals. Key in the growth and development of the fetus during pregnancy are the dynamics of glucocorticoids (GCs) and their binding protein,corticosteroid-binding globulin (CBG), which determines how much of the GCs are free and biologically active. Out of more than 5000 species of placental mammals in 19 different orders, our understanding of the dynamics of maternal GCs and CBG during pregnancy is largely limited to the detailed study of 3 groups - sheep, laboratory rodents, and humans. The assumption is often made that what we see in these few species applies to the rest. To examine this generality, we compared patterns of maternal GCs over pregnancy from all placental mammals where data is available: in the blood of 13 species from 5 different orders and in metabolites in excreta in an additional 20 species from 9 orders. We found that maternal free GCs increase by late pregnancy in most taxa. This increase is achieved by either an increase in total GC secretion or a decrease in CBG. A major exception is found in the even-toed ungulates (sheep, cows, etc.) where maternal GCs and CBG remain stable, but where the fetal adrenals mature in late pregnancy and produce the majority of their own GCs. We conclude that patterns of change in maternal GCs and CBG during pregnancy are species-specific but are alternative means to the same end: increased fetal exposure to GCs in late pregnancy, which is essential for development., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Community and ecosystem changes are happening in the pristine boreal forest ecosystem of the Yukon for 2 reasons. First, climate change is affecting the abiotic environment (temperature, rainfall and growing season) and driving changes in plant productivity and predator-prey interactions. Second, simultaneously change is occurring because of mammal species reintroductions and rewilding. The key ecological question is the impact these faunal changes will have on trophic dynamics. Primary productivity in the boreal forest is increasing because of climatic warming, but plant species composition is unlikely to change significantly during the next 50-100 years. The 9-10-year population cycle of snowshoe hares will persist but could be reduced in amplitude if winter weather increases predator hunting efficiency. Small rodents have increased in abundance because of increased vegetation growth. Arctic ground squirrels have disappeared from the forest because of increased predator hunting efficiency associated with shrub growth. Reintroductions have occurred for 2 reasons: human reintroductions of large ungulates and natural recolonization of mammals and birds extending their geographic ranges. The deliberate rewilding of wood bison (Bison bison) and elk (Cervus canadensis) has changed the trophic structure of this boreal ecosystem very little. The natural range expansion of mountain lions (Puma concolor), mule deer (Odocoileus hemionus) and American marten (Martes americana) should have few ecosystem effects. Understanding potential changes will require long-term monitoring studies and experiments on a scale we rarely deem possible. Ecosystems affected by climate change, species reintroductions and human alteration of habitats cannot remain stable and changes will be critically dependent on food web interactions., (© 2017 The Authors. Integrative Zoology published by International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.)

Crucial to the success of studies based on capture-mark-recapture (CMR) designs is the retention (permanency) and recognition (readability) of marks to identify individuals. Several marking methods for small mammals (< 60 g) are available, but their efficacy and use is not well known. We implemented a targeted survey of experts to gather their experiences and opinions regarding marking small mammals. Respondents (n = 114) stated their beliefs, perceptions, and current and future use, of marking methods, as well as factors influencing their choices, based on Likert and rank order scale questions. We compared responses based on where researchers' studies occurred, their level of experience, and their subfield of mammalogy. Most respondents (73%) had > 5 years experience marking small mammals, with 60% each marking > 1,000 individuals. Respondents believed that ear-tagging was most preferable in terms of efficiency, impact to affected animals (survival, pain), and personal ethics, whereas passive integrated transponder (PIT)-tagging was the most preferable with regard to retention and recognition, and toe-clipping with respect to cost. Most respondents plan to use ear-tagging (78%) or PIT-tagging (70%) in the future. PIT- and genetic-tagging are expected to increase, and toe-clipping to decline, in the future. The factors influencing which marking method respondents used were ranked—in order of decreasing preference—as impact, retention, recognition, cost, efficiency, and ethics. There were few differences in the mean response or consensus among respondents, regardless of their experience, location, or subfield. Most respondents (66%) agreed that additional studies on the performance and impact of various marking methods are needed to assess their costs and benefits for CMR-based studies. Ultimately, choice of marking method will depend on the species, research question, available resources, and local legislation and permitting. Our study, however, illustrates that collective insights by experienced mammalogists may aid individual researchers in deciding on study designs and protocols, particularly early career scientists. [ABSTRACT FROM AUTHOR]

Nonbreeding season territoriality is found in many mammal species irrespective of diet, being found in carnivores, granivores, and herbivores. However, we know the hormonal basis for this behavior in virtually none. American martens (Martes americana) show strong intrasexual, year-round territoriality. We collected serum samples from both territorial and transient males and documented size metrics and movement patterns with live-capture and radiotelemetry from September to June in 3 years in Southeast Alaska. Dehydroepiandrosterone (DHEA—a prohormone that can be converted in the brain to active gonadal hormones) levels were high (comparable to humans and rodents showing nonbreeding season spacing behavior) and did not change over the nonbreeding season in territorial males. In contrast, testosterone levels were low in autumn and increased as the summer breeding season approached. Territorial males were larger than transients in some measures and had higher testosterone levels, but similar DHEA and cortisol levels (total and free). DHEA levels declined with age. Our evidence is consistent with the hypothesis that DHEA, not testosterone, is the basis for territoriality outside the breeding season in martens, but collection of serum from females and experimental manipulations are required to provide conclusive evidence. [ABSTRACT FROM AUTHOR]

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The population dynamics of snowshoe hares ( Lepus americanus) are fundamental to the ecosystem dynamics of Canada's boreal forest. During the 8- to 11-year population cycle, hare densities can fluctuate up to 40-fold. Predators in this system (lynx, coyotes, great-horned owls) affect population numbers not only through direct mortality but also through sublethal effects. The chronic stress hypothesis posits that high predation risk during the decline severely stresses hares, leading to greater stress responses, heightened ability to mobilize cortisol and energy, and a poorer body condition. These effects may result in, or be mediated by, differential gene expression. We used an oligonucleotide microarray designed for a closely-related species, the European rabbit ( Oryctolagus cuniculus), to characterize differences in genome-wide hippocampal RNA transcript abundance in wild hares from the Yukon during peak and decline phases of a single cycle. A total of 106 genes were differentially regulated between phases. Array results were validated with quantitative real-time PCR, and mammalian protein sequence similarity was used to infer gene function. In comparison to hares from the peak, decline phase hares showed increased expression of genes involved in metabolic processes and hormone response, and decreased expression of immune response and blood cell formation genes. We found evidence for predation risk effects on the expression of genes whose putative functions correspond with physiological impacts known to be induced by predation risk in snowshoe hares. This study shows, for the first time, a link between changes in demography and alterations in neural RNA transcript abundance in a natural population. [ABSTRACT FROM AUTHOR]

Abstract: Wildlife capture methods can make it impractical or impossible to obtain baseline plasma glucocorticoid (GC) levels, and the time of capture of individual animals is often unknown so there may be little uniformity in the duration of capture-stress prior to blood collection. Although baseline samples are preferred, if seasonal changes in capture-stress GC levels closely reflect seasonal baseline changes, then capture-stress GC levels can be used to infer at least the direction of change in baseline levels; and if GC levels are relatively constant during long periods of capture, then lack of consistent capture durations are not problematic. These are empirical questions that need to be assessed for each species, and here we present our data for male Richardson’s ground squirrels (Urocitellus richardsonii) sampled in prebreeding and postbreeding periods. We compared cortisol levels in blood samples taken within 3min of capture (BASE), after 30min of capture-stress (STRESS-1), and after >1.5h of capture-stress (STRESS-2). We found that STRESS-2 cortisol levels did not change in unison with BASE levels, nor were STRESS-2 levels always equal to STRESS-1 levels. The importance of obtaining a baseline sample was further highlighted by our finding that prebreeding BASE cortisol levels were elevated to capture-stress-induced levels, leaving the animals almost no ability to respond to the stress of capture. In contrast, BASE cortisol levels in postbreeding animals were low and most animals responded robustly to capture. Those postbreeding animals that did not respond had high corticosteroid binding globulin levels that buffered the animals against the increase in total cortisol. STRESS-2 cortisol levels were useful for revealing how animals respond to sustained capture-stress, and revealed the same substantial variation among individuals observed in STRESS-1 blood samples, but they missed dramatic changes in baseline levels that are important for understanding the full context of seasonal changes in the functioning of the HPA axis. [Copyright &y& Elsevier]

The study of adult neurogenesis has had an explosion of fruitful growth. Yet numerous uncertainties and challenges persist. Our review begins with a survey of species that show evidence of adult neurogenesis. We then discuss how neurogenesis varies across brain regions and point out that regional specializations can indicate functional adaptations. Lifespan and aging are key life-history traits. Whereas 'adult neurogenesis' is the common term in the literature, it does not reflect the reality of neurogenesis being primarily a 'juvenile' phenomenon. We discuss the sharp decline with age as a universal trait of neurogenesis with inevitable functional consequences. Finally, the main body of the review focuses on the function of neurogenesis in birds and mammals. Selected examples illustrate how our understanding of avian and mammalian neurogenesis can complement each other. It is clear that although the two phyla have some common features, the function of adult neurogenesis may not be similar between them and filling the gaps will help us understand neurogenesis as an evolutionarily conserved trait to meet particular ecological pressures. [ABSTRACT FROM AUTHOR]

1. Prey responses to high predation risk can be morphological or behavioural and ultimately come at the cost of survival, growth, body condition, or reproduction. These sub-lethal predator effects have been shown to be mediated by physiological stress. We tested the hypothesis that elevated glucocorticoid concentrations directly cause a decline in reproduction in individual free-ranging female snowshoe hares, Lepus americanus. We measured the cortisol concentration from each dam (using a faecal analysis enzyme immunoassay) and her reproductive output (litter size, offspring birth mass, offspring right hind foot (RHF) length) 30 h after birth. 2. In a natural monitoring study, we monitored hares during the first and second litter from the population peak (2006) to the second year of the decline (2008). We found that faecal cortisol metabolite (FCM) concentration in dams decreased 52% from the first to the second litter. From the first to the second litter, litter size increased 122%, offspring body mass increased 130%, and offspring RHF length increased 112%. Dam FCM concentrations were inversely related to litter size ( r2 = 0·19), to offspring birth mass ( r2 = 0·32), and to offspring RHF length ( r2 = 0·64). 3. In an experimental manipulation, we assigned wild-caught, pregnant hares to a control and a stressed group and held them in pens. Hares in the stressed group were exposed to a dog 1–2 min every other day before parturition to simulate high predation risk. At parturition, unsuccessful-stressed dams (those that failed to give birth to live young) and stressed dams had 837% and 214%, respectively, higher FCM concentrations than control dams. Of those females that gave birth, litter size was similar between control and stressed dams. However, offspring from stressed dams were 37% lighter and 16% smaller than offspring from control dams. Increasing FCM concentration in dams caused the decline of offspring body mass ( r2 = 0·57) and RHF ( r2 = 0·52). 4. This is the first study in a free-ranging population of mammals to show that elevated, predator-induced, glucocorticoid concentrations in individual dams caused a decline in their reproductive output measured both by number and quality of offspring. Thus, we provide evidence that any stressor, not just predation, which increases glucocorticoid concentrations will result in a decrease in reproductive output. [ABSTRACT FROM AUTHOR]

In ecological risk assessment, a key necessity is to understand how contaminants known to have negative impact on laboratory mammals affect the population demography of mammals living in their natural environment. We examined the demography of six local populations of the short-tailed shrew (Blarina brevicauda) living in eastern deciduous forest palustrine habitat along the Housatonic River (MA, USA) on soils contaminated with a range of polychlorinated biphenyl (PCB) concentrations (1.5-38.3 ppm). The objective of the study was to assess whether PCBs adversely affect the population demography of these small mammals living in their natural environment. Blarina were selected for study because they would be expected to readily bioaccumulate PCBs from the soil. Populations were intensively live trapped on 1-ha grids from spring to autumn 2001. There was no relationship between any demographic parameter and PCB soil concentrations. Densities were high (usually exceeding 20/ha, and on two grids exceeded 60/ha in summer); survival was good (typically 60-75% per 30 d); and sex ratio, reproduction rates, growth rates, and body mass were within the ranges reported in the literature. Thus, these shrew populations showed no detectable impact on their population demography from living on PCB-contaminated sites. [ABSTRACT FROM AUTHOR]

In fluctuating environments, mothers may enhance the fitness of their offspring by adjusting offspring phenotypes to match the environment they will experience at independence. In free-ranging red squirrels, natural selection on offspring postnatal growth rates varies according to population density, with selection favoring faster-growing offspring under high-density conditions. We show that exposing mothers to high-density cues, accomplished via playbacks of territorial vocalizations, led to increased offspring growth rates in the absence of additional food resources. Experimental elevation of actual and perceived density induced higher maternal glucocorticoid levels, and females with naturally or experimentally increased glucocorticoids produced offspring that grew faster than controls. Therefore, social cues reflecting population density were sufficient to elicit increased offspring growth through an adaptive hormone-mediated maternal effect. [ABSTRACT FROM AUTHOR]

• Humans, rodents, and wild mammals share biological generalities in maternal programming. • Maternal androgens, photoperiod, microbiome and immunity influence offspring phenotype. • Milk is a rich source of maternal hormones, microbiota, immune factors and exosomes. • Milk exosomes transfer microRNA into offspring cells and may induce biological changes. • The extent of maternal programming cannot be fully understood by examining a single cue. The perinatal period is a sensitive time in mammalian development that can have long-lasting consequences on offspring phenotype via maternal effects. Maternal effects have been most intensively studied with respect to two major conditions: maternal diet and maternal stress. In this review, we shift the focus by discussing five major additional maternal cues and their influence on offspring phenotype: maternal androgen levels, photoperiod (melatonin), microbiome, immune regulation, and milk composition. We present the key findings for each of these topics in mammals, their mechanisms of action, and how they interact with each other and with the maternal influences of diet and stress. We explore their impacts in the contexts of both predictive adaptive responses and the developmental origins of disease, identify knowledge gaps and research opportunities in the field, and place a particular emphasis on the application and consideration of these effects in non-model species and natural ecological systems. [ABSTRACT FROM AUTHOR]