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The pace‐of‐life syndrome (POLS) hypothesis posits that consistent individual differences in behaviour are integrated with physiology and life‐history traits such that behaviour mediates how individuals resolve life‐history trade‐offs. For instance, individuals exhibiting higher exploration tendencies may accelerate reproduction by gaining access to resources more quickly, but this same behaviour could reduce survival through increased risks of predation and competition. While empirical support for POLS remains mixed, recent theory emphasises the role of environmental context in resolving some inconsistencies. Resource quality, in particular, may strongly mediate context‐dependent effects, yet its functional role has received little empirical attention. To address this, we monitored the complete life‐histories of 344 female house mice (Mus musculus domesticus) across four semi‐natural enclosures running in parallel, provisioned with either high or standard‐quality food. We first assessed how resource quality influenced life‐history traits and then repeatedly measured behaviour to investigate the among‐individual correlations between behaviour and life‐history within each food quality treatment. Two axes captured most of the variation in life‐history in both food quality treatments, with the primary axis reflecting a fast–slow continuum. The relationship between behaviour and life‐history was context‐dependent at the among‐individual level: under a lower quality treatment, more exploratory females exhibited a faster pace‐of‐life, consistent with a risk–mortality trade‐off. By contrast, in higher quality food conditions, individuals that covered more distance in an open‐field, that is, more active stress‐copers, delayed reproduction and followed a slower pace‐of‐life, suggesting a POLS that incorporates aspects of asset protection. Our results indicate that pace‐of‐life syndromes are context‐dependent, emerging most clearly when behavioural variation interacts with environmental factors that affect some aspect of fitness. More broadly, we provide evidence that POLS vary profoundly in different ecological conditions, highlighting the importance of considering environmental context when testing fundamental links between behaviour and life‐history. The correlation between behaviour and life‐history depends on environmental conditions. We show this is true when considering the quality of the food in the environment.

The pace-of-life syndrome (POLS) hypothesis predicts that behavior and physiology covary with life history. Evidence for such covariation is contradictory, possibly because systematic sources of variation (e.g. sex) have been neglected. Sexes often experience different selection pressures leading to sex-specific allocation between reproduction and self-maintenance, facilitating divergence in life-history. Sex-specific differences in means and possibly variances may therefore play a key role in the POLS framework. We investigate whether sexes differ in means and variances along the fast-slow pace-of-life continuum for life history and physiological and behavioral traits. In addition, we test whether social and environmental characteristics such as breeding strategy, mating system, and study environment explain heterogeneity between the sexes. Using meta-analytic methods, we found that populations with a polygynous mating system or for studies conducted on wild populations, males had a faster pace-of-life for developmental life-history traits (e.g., growth rate), behavior, and physiology. In contrast, adult life-history traits (e.g., lifespan) were shifted towards faster pace-of-life in females, deviating from the other trait categories. Phenotypic variances were similar between the sexes across trait categories and were not affected by mating system or study environment. Breeding strategy did not influence sex differences in variances or means. We discuss our results in the light of sex-specific selection that might drive sex-specific differences in pace-of-life and ultimately POLS.

The pace-of-life syndrome hypothesis predicts that individual differences in behavior should integrate with morphological, physiological, and life-history traits along a slow to fast pace-of-life continuum. For example, individuals with a \"slow\" pace-of-life are expected to exhibit a slower growth rate, delayed reproduction, longer lifespans, have stronger immune responses, and are expected to avoid risky situations relative to \"fast\" individuals. If supported, this hypothesis would help resolve ecological and evolutionary questions regarding the origin and maintenance of phenotypic variation. Support for the pace-of-life syndrome hypothesis has, however, been mixed. Here, we conducted a meta-analysis of 42 articles and 179 estimates testing the pace-of-life syndrome hypothesis as it applies to the integration of behaviors with physiological or life-history traits. We found little overall support for the pace-of-life syndrome hypothesis with the mean support estimated as r = 0.06. Support for the pace-of-life syndrome hypothesis was significantly higher in invertebrates (r=0.23) than vertebrates (r=0.02) and significantly higher when based on phenotypic (r=0.10) versus genetic correlations (r=–0.09). We a lso found that females exhibited correlations between behavior and life-history and physiology that were opposite the predictions of the pace-of-life syndrome hypothesis (r=-0.16) and that these correlations significantly differed from those observed in males (r=0.01) or males and females pooled (r=0.12). It was also the case that there was little support for the hypothesis when life-history and physiological traits were independently analyzed (behavior × life-history: r=0.12; behavior × physiology: r=0.04). Exploratory post hoc analyses revealed that correlations of behavior with growth rate and hormone levels were more likely to show support for the predictions of the pace-of-life syndrome hypothesis. The lack of overall support found in our analyses suggests that general assertions regarding phenotypic integration due to \"pace-of-life\" should be re-evaluated.

The pace-of-life syndrome (i.e., POLS) hypothesis posits that behavioral and physiological traits mediate the trade-off between current and future reproduction. This hypothesis predicts that life history, behavioral, and physiological traits will covary under clearly defined conditions. Empirical tests are equivocal and suggest that the conditions necessary for the POLS to emerge are not always met. We nuance and expand the POLS hypothesis to consider alternative relationships among behavior, physiology, and life history. These relationships will vary with the nature of predation risk, the challenges posed by resource acquisition, and the energy management strategies of organisms. We also discuss how the plastic response of behavior, physiology, and life history to changes in ecological conditions and variation in resource acquisition among individuals determine our ability to detect a fast-slow pace of life in the first place or associations among these traits. Future empirical studies will provide most insights on the coevolution among behavior, physiology, and life history by investigating these traits both at the genetic and phenotypic levels in varying types of predation regimes and levels of resource abundance.

Summary A phenotypic syndrome refers to complex patterns of integration among functionally related traits in an organism that defines how the organism interacts with its environment and sustains itself. Human‐induced biological invasions have become important sources of environmental modifications. However, the extent to which invasive species affect the phenotypic syndromes of individuals in a native is currently unknown. Such knowledge has important implications for understanding ecological interactions and the management of biological invasions. Here, field monitoring in a natural stream were combined with standardized estimates of behavioral, physiological and morphological traits to address the hypothesis that coexistence with a non‐native invader induces a novel environmental pressure that disrupts the adaptive integration among phenotypic traits of the native species. We compared the strength of integration among key phenotypic traits (i.e. aerobic scope, standard metabolic rate, body growth, activity, and body shape) and ecological niche traits (i.e. spring and summer diet, home range size, daily movements) of an allopatric group of native brown trout (Salmo trutta) with a group of brown trout living in sympatry with non‐native brook trout (Salvelinus fontinalis). We found that the integration of phenotypic traits was substantially reduced in the sympatric brown trout and that allopatric and sympatric brown trout differed in key phenotypic and ecological niche traits. Brown trout living in sympatry with non‐native brook trout consumed more terrestrial prey, had smaller home ranges, and a stouter body shape. Sympatric brown trout also had lower specific growth rate, suggesting a lower fitness. The results are generally in line with our hypothesis suggesting that the reduction in fitness observed in sympatric brown trout is caused by the breakdown of their adaptive phenotypic syndrome. This may be caused by differences in the plasticity of the response of phenotypic traits to the novel selection pressure induced by the non‐native species. Our results may help explaining deleterious effects of non‐native species reported in the absence of direct competition with the native species. A lay summary is available for this article. Lay Summary

Multiple species show significant trait shifts in response to urbanization. Yet, the impact of anthropogenic warming linked to the urban heat island effect is remarkably understudied. In addition, the relative contributions of phenotypic plasticity and genetic change underlying trait shifts in response to urbanization are poorly known. A common garden study with the water flea Daphnia magna revealed that both genetic differentiation in response to urbanization and phenotypic plasticity in response to higher rearing temperature (24°C) induced significant parallel multivariate shifts in life‐history strategy along the slow–fast pace‐of‐life axis. Urban animals and animals reared at higher temperatures are characterized by fast maturation, early release of progeny, a smaller size at maturity, increased fecundity and higher performance (given by maximal population growth rate “r”) compared to genotypes isolated from rural ponds and animals reared at lower temperatures, respectively. Evolution in response to urbanization accounted for 30% of the total observed shift in life history and caused a significant change in mean trait values, while plasticity responses to experimental warming were unaltered between urban and rural populations. The total trait change achieved through both plasticity and evolution ranged from 8% to 56% depending on the trait. Our results provide clear evidence for evolution underlying an increase in pace of life of populations in response to urbanization. Given the pivotal role of Daphnia in aquatic ecosystems, this shift potentially feeds back to population structure, top‐down control of algae and food web dynamics in urban freshwater ecosystems. In addition, we argue that adaptation to urban heat islands might render these populations preadapted in a context of future climate change. plain language summary is available for this article. Plain Language Summary

Life span and aging are substantially modified by natural selection. Across species, higher extrinsic (environmentally related) mortality (and hence shorter life expectancy) selects for the evolution of more rapid aging. However, among populations within species, high extrinsic mortality can lead to extended life span and slower aging as a consequence of condition-dependent survival. Using within-species contrasts of eight natural populations of Nothobranchius fishes in common garden experiments, we demonstrate that populations originating from dry regions (with short life expectancy) had shorter intrinsic life spans and a greater increase in mortality with age, more pronounced cellular and physiological deterioration (oxidative damage, tumor load), and a faster decline in fertility than populations from wetter regions. This parallel intraspecific divergence in life span and aging was not associated with divergence in early life history (rapid growth, maturation) or pace-of-life syndrome (high metabolic rates, active behavior). Variability across four study species suggests that a combination of different aging and life-history traits conformed with or contradicted the predictions for each species. These findings demonstrate that variation in life span and functional decline among natural populations are linked, genetically underpinned, and can evolve relatively rapidly.

Physiology and temperature can both have a profound influence on behaviour and metabolism. Despite this, thermal physiology has rarely been considered within the animal personality framework, but could be an inherent mechanism maintaining consistent individual differences in behaviour, particularly in species that need to thermoregulate (i.e. ectotherms). Here, we present evidence for a thermal‐behavioural syndrome and detail how it is linked to variation in habitat selection in an Australian lizard, the delicate skink, Lampropholis delicata. We predicted that individuals would occur along a cold–hot continuum—analogues to the slow–fast continuum proposed by the pace‐of‐life hypothesis—whereby an individual's placement along a thermal physiological axis will correspond with their placement along a personality axis. We first tested the thermal‐behavioural syndrome by measuring the thermal preferences and optimal performance temperature of individual skinks and linking it to their activity, exploratory, social and boldness behaviours. In line with our predictions, we found that individuals with a “hot” thermal type performed optimally at higher temperatures, had faster sprint speeds and were more active, explorative and bold relative to “cold” thermal types. We then monitored each individual's habitat selection within an artificial environment containing three microhabitats differing in their thermal characteristics. We found that an individual's thermal type mediated their use of habitat, in which “hot” individuals utilized a hotter microhabitat more regularly than both “cold” and “intermediate” thermal types, suggesting that the thermal‐behavioural syndrome could drive ecological niche partitioning in this species. We envisage that the thermal‐behavioural syndrome concept is likely to extend to other study systems, particularly to ectothermic organisms that rely heavily on behavioural thermoregulation to maintain optimal body temperature. A plain language summary is available for this article. Plain Language Summary

Despite growing appreciation of the importance of considering a pace-of-life syndrome (POLS) perspective to understand how animals interact with their environment, studies relating behavior to life history under altered environmental conditions are still rare. By means of a comparative analysis of flight initiation distances (i.e., the distance at which an animal takes flight when a human being is approaching) across > 300 bird species distributed worldwide, we document here the existence of a POLS predicted by theory where slow-lived species tend to be more risk-averse than fast-lived species. This syndrome largely emerges from the influence of body mass, and is highly dependent on the environmental context. Accordingly, the POLS structure vanishes in urbanized environments due to slow-lived species adjusting their flight distances based on the perception of risk. While it is unclear whether changes in POLS reflect plastic and/or evolutionary adjustments, our findings highlight the need to integrate behavior into life history theory to fully understand how animals tolerate human-induced environmental changes.

Significance Forecasting reservoirs of zoonotic disease is a pressing public health priority. We apply machine learning to datasets describing the biological, ecological, and life history traits of rodents, which collectively carry a disproportionate number of zoonotic pathogens. We identify particular rodent species predicted to be novel zoonotic reservoirs and geographic regions from which new emerging pathogens are most likely to arise. We also describe trait profiles—complexes of biological features—that distinguish reservoirs from nonreservoirs. Generally, the most permissive rodent reservoirs display a fast-paced life history strategy, maximizing near-term fitness by having many altricial young that begin reproduction early and reproduce frequently. These findings may constitute an important lead in guiding the search for novel disease reservoirs in the wild. The increasing frequency of zoonotic disease events underscores a need to develop forecasting tools toward a more preemptive approach to outbreak investigation. We apply machine learning to data describing the traits and zoonotic pathogen diversity of the most speciose group of mammals, the rodents, which also comprise a disproportionate number of zoonotic disease reservoirs. Our models predict reservoir status in this group with over 90% accuracy, identifying species with high probabilities of harboring undiscovered zoonotic pathogens based on trait profiles that may serve as rules of thumb to distinguish reservoirs from nonreservoir species. Key predictors of zoonotic reservoirs include biogeographical properties, such as range size, as well as intrinsic host traits associated with lifetime reproductive output. Predicted hotspots of novel rodent reservoir diversity occur in the Middle East and Central Asia and the Midwestern United States.