Ben Dantzer

• PhD, Michigan State University
• Professor (Assistant) at University of Michigan

In cooperative breeders, aggression from dominant breeders directed at subordinates may raise subordinate stress hormone (glucocorticoid) concentrations. This may benefit dominants by suppressing subordinate reproduction but it is uncertain whether aggression from dominants can elevate subordinate cooperative behaviour, or how resulting changes in...

Measures of glucocorticoid stress hormones (e.g. cortisol) have often been used to characterize conflict between subordinates and dominants. In cooperative breeders where subordinates seldom breed in their natal group and assist in offspring rearing, increases in subordinate glucocorticoid levels may be caused by conflict among subordinates as well...

Synopsis Hormonal pleiotropy occurs when a part of the endocrine system (e.g., hormone concentrations) influences the expression of two or more phenotypes. Although hormonal pleiotropy may have similar evolutionary consequences as genetic pleiotropy, most conceptual and empirical work on its putative evolutionary consequences to date has focused on...

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...

Life-history traits describe parameters associated with growth, size, survival, and reproduction. Life-history variation is a hallmark of biological diversity, yet researchers commonly observe that one of the major axes of life-history variation after controlling for body size involves trade-offs among growth, reproduction, and longevity. This pers...

There are barriers to directly observing animals that are cryptic or live in environments inaccessible to humans. Biologgers, animal-attached devices designed to collect data on animals without a human researcher present, have become useful tools for studying species that cannot be directly observed. The use of biologgers has been size-limited unti...

1. Phenotypic plasticity is a central avenue through which organisms cope with environmental heterogeneity by responding to cues of current environmental change to maximize fitness. If environmental change is impending and cues can reliably predict future conditions, organisms can also mount adaptive responses in anticipation of these changes if th...

Microbial transmission is a major benefit of sociality, facilitated by affiliative behaviors such as grooming and communal nesting in group living animals. The spread of microbial symbionts through these pathways, and their incorporation into host microbiomes, can enhance host health and fitness by contributing to pathogen protection and metabolic...

Studying animal social systems requires understanding variations in contact and interaction, influenced by factors, such as environmental conditions, resource availability, and predation risk. Traditional observational methods have limitations, but advancements in sensor technologies and data analytics provide new opportunities. We developed a wire...

Urbanization presents a myriad of challenges to wildlife, yet some individuals or species persist and even thrive in urban environments. Specific behavioral traits that have been proposed to enable animals to cope with challenges and frequently observed in urban wildlife populations across many taxonomic groups include changes in docility, activity...

Early-life adversity, even when transient, can have lasting effects on individual phenotypes and reduce lifespan across species. If these effects can be mitigated by a high-quality later-life environment, then differences in future resources may explain variable resilience to early-life adversity. Using data from over 1000 wild North American red s...

An increase in maternal stress during offspring development can have cascading, life-long impacts on offspring behavior and physiology, which can vary depending on the timing of exposure to the stressor. By responding to stressors through increasing production of glucocorticoids (GCs), the hypothalamic-pituitary-adrenal (HPA) axis is a key mediator...

Female advertisement of reproductive state and receptivity has the potential to play a large role in the mating systems of many taxa, but investigations of this phenomenon are underrepresented in the literature. North American red squirrels (Tamiasciurus hudsonicus) are highly territorial and engage in scramble competition mating, with males conver...

Understanding the dynamics of animal social systems requires studying variation in contact and interaction, which is influenced by environmental conditions, resource availability, and predation risk, among other factors. Traditional (direct) observational methods have limitations, but advancements in sensor technologies and data analytics provide u...

Many studies assume that it is beneficial for individuals of a species to be heavier, or have a higher body condition index (BCI), without accounting for the physiological relevance of variation in the composition of different body tissues. We hypothesized that the relationship between BCI and masses of physiologically important tissues (fat and le...

Gut microbiomes are diverse ecosystems whose drivers of variation remain largely unknown, especially in time and space. We analysed a dataset with over 900 red squirrel (Tamiasciurus hudsonicus) gut microbiome samples to identify the drivers of gut microbiome composition in this territorial rodent. The large‐scale spatiotemporal replication in the...

Many studies assume that it is beneficial for individuals of a species to be heavier, or have a higher body condition index (BCI), without accounting for the physiological relevance of variation in the composition of different body tissues. We hypothesized that the relationship between BCI and masses of physiologically important tissues (fat and le...

Understanding if and how individuals and populations cope with environmental change is an enduring question in evolutionary ecology that has renewed importance given the pace of change in the Anthropocene. Two evolutionary strategies of coping with environmental change may be particularly important in rapidly changing environments: adaptive phenoty...

Mismatches between an organism's phenotype and its environment can result in short-term fitness costs. Here, we show that some phenotype-environment mismatch errors can be explained by asymmetrical costs of different types of errors in wild red squirrels. Mothers that mistakenly increased reproductive effort when signals of an upcoming food pulse w...

While cooperative interactions among kin are a key building block in the societies of group-living species, their importance for species with more variable social environments is unclear. North American red squirrels (Tamiasciurus hudsonicus) defend individual territories in dynamic neighbourhoods and are known to benefit from living among familiar...

Territories are typically defined as spatially exclusive areas that are defended against conspecifics. Given the spatial nature of territoriality, it is inherently density dependent, but the economics of territoriality also depend on the distribution and abundance of defended resources. Our objectives were to assess the effects of changing populati...

Evolutionary endocrinology aims to understand how natural selection shapes endocrine systems and the degree to which endocrine systems themselves can induce phenotypic responses to environmental changes. Such responses may be specialized in that they reflect past selection for responsiveness only to those ecological factors that ultimately influenc...

Reproduction is an energetically expensive activity for both sexes. However, if males and females differ in their annual timing of reproduction, such that peak investment for one sex occurs during a more resource-limited period, there is an opportunity for sex-specific selection to act on the acquisition of energetic resources. Both male and female...

Wind speed can have multifaceted effects on organisms including altering thermoregulation, locomotion, and sensory reception. While forest cover can substantially reduce wind speed at ground level, it is not known if animals living in forests show any behavioural responses to changes in wind speed. Here, we explored how three boreal forest mammals,...

Animals cope with environmental perturbations through the stress response, a set of behavioural and physiological responses aimed to maintain and/or return to homeostasis and enhance fitness. Vertebrate neuroendocrine axis activation in response to environmental stressors can result in the secretion of glucocorticoids (GCs), whose acute increases m...

Animal-borne sensors that can record and transmit data (“biologgers”) are becoming smaller and more capable at a rapid pace. Biologgers have provided enormous insight into the covert lives of many free-ranging animals by characterizing behavioral motifs, estimating energy expenditure, and tracking movement over vast distances, thereby serving both...

In continuously changing environments, variation of different ecological factors could affect the functioning of the hypothalamic-pituitary-adrenal (HPA) axis in wild mammals, increasing the secretion of glucocorticoids (GCs). In different animal species, GC concentrations are often used as a measure of the physiological stress response to environm...

Animal species vary in whether they provide parental care or the type of care provided, and this variation in parental care among species has been a common focus of comparative studies. However, the proximate causes and ultimate consequences of within-species variation in parental care have been less studied. Most studies about the impacts of withi...

The effect of the social environment on individual state or condition has largely focused on glucocorticoid levels (GCs). As metabolic hormones whose production can be influenced by nutritional, physical, or psychosocial stressors, GCs are a valuable (though singular) measure that may reflect the degree of “stress” experienced by an individual. Mos...

As interest in animal personality research grows, methodologies for quantifying consistent among-individual differences in behaviour are expanding. Two of the most common methods for quantifying animal personality are standardized behavioural assays and focal animal sampling. We evaluated whether assays and focals provided similar animal personalit...

The gut microbiome impacts host health and fitness, in part through the diversification of gut metabolic function and pathogen protection. Elevations in glucocorticoids (GCs) appear to reduce gut microbiome diversity in experimental studies, suggesting that a loss of microbial diversity may be a negative consequence of increased GCs. However, given...

Significant gaps remain in understanding the response of plant reproduction to environmental change. This is partly because measuring reproduction in long-lived plants requires direct observation over many years and such datasets have rarely been made publicly available. Here we introduce MASTREE+, a dataset that collates reproductive time-series d...

For regions that were covered by ice during the Pleistocene glaciations, species must have emigrated from unglaciated regions. However, it can be difficult to discern when and from what ancestral source populations such expansions took place, especially since warming climates introduce the possibility of very recent expansions. For example, in the...

The data, meta-data, and code for how selective disappearance and fluctuating selection maintain animal personality in North American red squirrels (Tamiasciurus hudsonicus) in Yukon, Canada. Data obtained with funding from the Natural Sciences and Engineering Council of Canada, Northern Scientific Training Program, and the National Science Foundat...

While cooperative interactions among kin are a key building block in the societies of group-living mammals, their importance for species with more variable social environments is unclear. North American red squirrels (Tamiasciurus hudsonicus) defend individual territories in dynamic neighbourhoods and are known to benefit from living among familiar...

When resources are limited, mean fitness is constrained and competition can cause genes and phenotypes to enhance an individual’s own fitness while reducing the fitness of their competitors. Negative social effects on fitness have the potential to constrain adaptation, but the interplay between ecological opportunity and social constraints on adapt...

Sleep is appreciated as a behavior critical to homeostasis, performance, and fitness. Yet, most of what we know about sleep comes from humans or controlled laboratory experiments. Assessing sleep in wild animals is challenging, as it is often hidden from view, and electrophysiological recordings that define sleep states are difficult to obtain. Acc...

Gut microbiome diversity plays an important role in host health and fitness, in part through the diversification of gut metabolic function and pathogen protection. Elevations in glucocorticoids (GCs) appear to reduce gut microbiome diversity in experimental studies, suggesting that a loss of microbial diversity may be a negative consequence of incr...

Animals in urban areas that experience frequent exposure to humans often behave differently than those in less urban areas, such as exhibiting less vigilance or anti-predator behavior. These behavioral shifts may be an adaptive response to urbanization, but it may be costly if animals in urban areas also exhibit reduced anti-predator behavior in th...

A wide range of species have been found to differentiate kin from nonkin. However, the ability to recognize kin, or the costs and benefits of discriminating kin from nonkin may depend on particular extrinsic environmental or intrinsic physiological conditions, resulting in context-dependent kin discrimination. North American red squirrels, Tamiasci...

Environmental change and biodiversity loss are but two of the complex challenges facing conservation practitioners and policy makers. Relevant and robust scientific knowledge is critical for providing decision-makers with the actionable evidence needed to inform conservation decisions. In the Anthropocene, science that leads to meaningful improveme...

As a response to environmental cues, maternal glucocorticoids (GCs) may trigger adaptive developmental plasticity in the physiology and behavior of offspring. In North American red squirrels ( Tamiasciurus hudsonicus ), mothers exhibit increased GCs when conspecific density is elevated, and selection favors more aggressive and perhaps more active m...

Understanding the causes and consequences of repeatable among-individual differences in behavior (i.e., animal personality) is a major area of research in behavioral and evolutionary ecology. Recently, attention has turned to understanding the processes behind changes in repeatability through ontogeny because of their implications for populations....

One common theme of adaptive hypotheses for the existence of stable individual differences in behavior (personality) or persistent correlations among behaviors (behavioral syndromes) is an association between intrinsic state (e.g., body size, mass, metabolism) and the behavioral traits of interest. Empiricists are tasked with assessing whether ther...

Animals in urban areas that experience frequent exposure to humans often behave differently than those in less urban areas, such as less vigilance or anti-predator behavior. These behavioral shifts may be an adaptive response to urbanization and caused by habituation to humans. A possible negative consequence is cross-habituation to natural predato...

One of the outstanding questions in evolutionary biology is the extent to which mutually beneficial interactions and kin-selection can facilitate the evolution of cooperation by mitigating conflict between interacting organisms. The indirect fitness benefits gained from associating with kin are an important pathway to conflict resolution [1], but c...

One of the outstanding questions in evolutionary biology is the extent to which mutually beneficial interactions and kin selection can facilitate the evolution of cooperation by mitigating conflict between interacting organisms. The indirect fitness benefits gained from associating with kin are an important pathway to conflict resolution,¹ but conf...

Long‐term studies of wild animals provide the opportunity to investigate how phenotypic plasticity is used to cope with environmental fluctuations and how the relationships between phenotypes and fitness can be dependent upon the ecological context. Many previous studies have only investigated life‐history plasticity in response to changes in tempe...

Environmental factors experienced during development can affect the physiology and behavior of offspring. Maternal glucocorticoids (GCs) may convert environmental cues experienced by the mother into a cue triggering adaptive developmental plasticity in offspring. In North American red squirrels ( Tamiasciurus hudsonicus ), females exhibit increases...

The pace-of-life syndrome hypothesis posits that personality traits (i.e. consistent individual differences in behaviour) are linked to life history and fitness. Specifically, fast-paced individuals are predicted to be proactive (i.e. active and aggressive) with an earlier age at first reproduction, a shorter life span and higher fecundity than slo...

Organisms survive environmental variation by combining homeostatic regulation of critical states with allostatic variation of other traits, and species differences in these responses can contribute to coexistence in temporally variable environments. In this paper, we simultaneously record variation in three functional traits—body temperature (Tb),...

Short-term elevation of glucocorticoids (GCs) is one of the major physiological mechanisms by which vertebrates cope with challenging environmental or social factors (stressors). However, when exposure to stressors occurs repeatedly or over a prolonged period of time, animals may experience chronic elevation of GCs, which reduces the immune respons...

Short-term elevation of glucocorticoids (GCs) is one of the major physiological mechanisms by which vertebrates cope with challenging environmental or social factors (stressors). However, when exposure to stressors occurs repeatedly or over a prolonged period of time, animals may experience chronic elevation of GCs, which reduces the immune respons...

Parental investment theory predicts that observed levels of parental care afforded to offspring are set by the benefits (to offspring quality and survival) relative to the costs (to parental survival or future reproduction). Although difficult to document in mammals, there is often substantial individual variation in the amount of parental care wit...

Comparative studies aid in our understanding of specific conditions favouring the initial evolution of different types of social behaviours, yet there is much unexplained intraspecific variation in the expression of social behaviour that comparative studies have not yet addressed. The proximate causes of this individual variation in social behaviou...

R code and supplementary material used in publication. Hendrix, J. G., D. N. Fisher, A. R. Martinig, S. Boutin, B. Dantzer, J. E. Lane, and A. G. McAdam. 2020. Territory acquisition mediates the influence of predators and climate on juvenile red squirrel survival. Journal of Animal Ecology 89:1408-1418. DOI: 10.1111/1365-2656.13209

Juvenile survival to first breeding is a key life‐history stage for all taxa. Survival through this period can be particularly challenging when it coincides with harsh environmental conditions such as a winter climate or food scarcity, leading to highly variable cohort survival. However, the small size and dispersive nature of juveniles generally m...

Infographic for "Territory acquisition mediates the influence of predators and climate on juvenile red squirrel survival"

Applying physiological tools, knowledge and concepts to understand conservation problems (i.e. conservation physiology) has become commonplace and confers an ability to understand mechanistic processes, develop predictive models and identify cause-and-effect relationships. Conservation physiology is making contributions to conservation solutions; t...

Glucocorticoids are involved in regulation of an animal’s energetic state. Under stressful situations, they are part of the neuroendocrine response to cope with environmental challenges. Animals react to aversive stimuli also through behavioural responses, defined as coping styles. Both in captive and wild populations, individuals differ in their b...

Animals switch between inactive and active states, simultaneously impacting their energy intake, energy expenditure and predation risk, and collectively defining how they engage with environmental variation and trophic interactions. We assess daily activity responses to long‐term variation in temperature, resources and mating opportunities to exami...

Quantifying how whole organisms respond to challenges in the external and internal environment ("stressors") is difficult. To date, physiological ecologists have mostly used measures of glucocorticoids (GCs) to assess the impact of stressors on animals. This is of course too simplistic as Hans Seyle himself characterized the response of organisms t...

Infographic: The new kid on the block: immigrant males win big whereas females pay fitness cost after dispersal

Dispersal is nearly universal; yet, which sex tends to disperse more and their success thereafter depends on the fitness consequences of dispersal. We asked if lifetime fitness differed between residents and immigrants (successful between-population dispersers) and their offspring using 29 years of monitoring from North American red squirrels (Tami...

Elevations in glucocorticoid levels (GCs) in breeding females may induce adaptive shifts in offspring life histories. Offspring produced by mothers with elevated GCs may be better prepared to face harsh environments where a faster pace of life is beneficial. We examined how experimentally elevated GCs in pregnant or lactating North American red squ...

The pace of life syndrome hypothesis posits that personality traits (i.e., consistent individual differences in behaviour) are linked to life history and fitness. Specifically, fast-paced individuals are predicted to be proactive (i.e., active and aggressive) with an earlier age at first reproduction, a shorter lifespan, and a higher fecundity than...

Quantifying the impact of changes or stimuli in the external and internal environment that are challenging (“stressors”) to whole organisms is difficult. To date, physiological ecologists and ecological physiologists have mostly used measures of glucocorticoids (GCs) to assess the impact of stressors on animals. This is of course too simplistic as...

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 anc...

Individuals vary in their behavioral and physiological responses to environmental changes. These behavioral responses are often described as “coping styles” along a proactive-reactive continuum. Studies in laboratory populations often, but not always, find that behavioral responses and physiological responses to stressors covary, where more proacti...

Phenotypic plasticity - one individual's capacity for phenotypic variation under different environments - is critical for organisms facing fluctuating conditions within their lifetime. North American red squirrels (Tamiasciurus hudsonicus) experience drastic among-year fluctuations in conspecific density. This shapes juvenile competition over vacan...

Acoustic signaling is an important means by which animals communicate both stable and labile characteristics. Although it is widely appreciated that vocalizations can convey information on labile state, such as fear and aggression, fewer studies have experimentally examined the acoustic expression of stress state. The transmission of such public in...

Hormones such as glucocorticoids (colloquially referred to as "stress hormones") have important effects on animal behavior and life-history traits, yet most of this understanding has come through correlative studies. While experimental studies offer the ability to assign causality, there are important methodological concerns that are often not cons...

Elevations in glucocorticoid levels (GCs) in breeding females may induce adaptive shifts in offspring life histories. Offspring produced by mothers with elevated GCs may be better prepared to face harsh environments where a faster pace of life is beneficial. We examined how experimentally elevated GCs in pregnant or lactating North American red squ...

Comparative studies aid in our understanding of specific conditions favoring the initial evolution of different types of social behaviors, yet there is much unexplained intraspecific variation in the expression of social behavior that comparative studies have not yet addressed. The proximate causes of this individual variation in social behavior wi...

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 anc...

Phenotypic plasticity, one individual's capacity for phenotypic variation under different environments, is critical for organisms facing fluctuating conditions within their lifetime. North American red squirrels (Tamiasciurus hudsonicus) experience drastic among-year fluctuations in conspecific density. This shapes juvenile competition over vacant...

For territorial species, the ability to be behaviourally plastic in response to changes in their social environment may be beneficial by allowing individuals to mitigate conflict with conspecifics and reduce the costs of territoriality. Here we investigated whether North American red squirrels, Tamiasciurus hudsonicus, are able to minimize costs of...

The episodic production of large seed crops by some perennial plants (masting) is known to increase seed escape by alternately starving and swamping seed predators. These pulses of resources might also act as an agent of selection on the life histories of seed predators, which could indirectly enhance seed escape by inducing an evolutionary load on...

Juvenile survival to first breeding is a key life history stage. Survival through this period can be particularly challenging when it coincides with harsh environmental conditions like winter climate or food scarcity, and so cohort survival can be highly variable. However, the small size and dispersive nature of juveniles makes studying their survi...

Parental investment theory predicts that observed levels of parental care afforded to offspring are set by the benefits (to offspring quality and survival) relative to the costs (to parental survival or future reproduction). Although difficult to document in mammals, there is often substantial individual-variation in the amount of parental care wit...

A central assumption of hypotheses for the evolution of animal dispersal is that dispersal incurs a cost, which is later compensated for through increased fitness. However, the empirical data needed to test this assumption are logistically challenging to collect. Using 30 years of demographic and genetic data from a population of North American red...

Organisms can affect one another's phenotypes when they socially interact. Indirect genetic effects occur when an individual's phenotype is affected by genes expressed in another individual. These heritable effects can enhance or reduce adaptive potential, thereby accelerating or reversing evolutionary change. Quantifying these social effects is th...

The phenotype of parents can have long-lasting effects on the development of offspring as well as on their behaviour, physiology and morphology as adults. In some cases, these changes may increase offspring fitness but, in others, they can elevate parental fitness at a cost to the fitness of their offspring. We show that in Kalahari meerkats ( Suri...

Interactions between organisms are ubiquitous and have important consequences for phenotypes and fitness. Individuals can even influence those they never meet, if they have extended phenotypes that alter the environments others experience. North American red squirrels (Tamiasciurus hudsonicus) guard food hoards, an extended phenotype that typically...

The episodic production of large seed crops by some perennial plants, is referred to as masting and is known to increase seed escape by alternately starving and swamping seed predators. These pulses of resources, however, might also act as an agent of selection on the life histories of seed predators, which could indirectly enhance seed escape by i...

Fisher's principle explains that population sex ratio in sexually reproducing organisms is maintained at 1 : 1 owing to negative frequency-dependent selection, such that individuals of the rare sex realize greater reproductive opportunity than individuals of the more common sex until equilibrium is reached. If biasing offspring sex ratio towards th...

Accurately recording the social and mating behavior of wild animals is necessary to test hypotheses regarding the evolution of monogamous behavior but documenting the behavior of most wild animals is challenging. Social network analyses can use patterns of spatial and temporal co-occurrence to describe the social associations of individuals within...

Individuals vary in their behavioral and physiological responses to environmental changes. These behavioral responses are often described as ‘coping styles’ along a proactive-reactive continuum. Studies in laboratory populations often, but not always, find that behavioral responses and physiological responses to stressors covary, where more proacti...

Acoustic signaling is an important means by which animals communicate both stable and labile characteristics. Although it is widely appreciated that vocalizations can convey information on labile state, such as fear and aggression, very few studies have experimentally examined the acoustic expression of short-term stress state. The transmission of...

For territorial species, the ability to be behaviourally plastic in response to changes in their social environment may be beneficial by allowing individuals to mitigate conflict with conspecifics and reduce the costs of territoriality. Here we investigated whether North American red squirrels (Tamiasciurus hudsonicus) were able to minimize costs o...

Territoriality arises when the benefits of resources exceed the costs of defending them. The dear enemy phenomenon, where familiar territorial neighbours refrain from intruding on one another and mutually reduce their defensive efforts, allows for reduction of these costs but requires discrimination between conspecifics. We hypothesized that territ...

In many species, territory defense is thought to be one of the primary functions of acoustic communication. North American red squirrels are a territorial species in which 'rattles' have long been thought to be the principal signal communicating territory ownership. These vocalizations have been assumed to deter intruders, thus reducing energy cost...

Territoriality arises when the benefits of resources exceed the costs of defending them. The dear enemy phenomenon, where familiar territorial neighbours refrain from intruding on one another and mutually reduce their defensive efforts, allows for reduction of these costs but requires discrimination between conspecifics. We hypothesized that territ...