The ecology of exercise: mechanisms underlying Individual variation in behavior, activity, and performance: an introduction to symposium

Wild animals often engage in intense physical activity while performing tasks vital for their survival and reproduction associated with foraging, avoiding predators, fighting, providing parental care, and migrating. In this theme issue we consider how viewing these tasks as “exercise”—analogous to that performed by human athletes—may help provide insight into the mechanisms underlying individual variation in these types of behaviors and the importance of physical activity in an ecological context. In this article and throughout this issue, we focus on four key questions relevant to the study of behavioral ecology that may be addressed by studying wild animal behavior from the perspective of exercise physiology: (1) How hard do individual animals work in response to ecological (or evolutionary) demands?; (2) Do lab-based studies of activity provide good models for understanding activity in free-living animals and individual variation in traits?; (3) Can animals work too hard during “routine” activities?; and (4) Can paradigms of “exercise” and “training” be applied to free-living animals? Attempts to address these issues are currently being facilitated by rapid technological developments associated with physiological measurements and the remote tracking of wild animals, to provide mechanistic insights into the behavior of free-ranging animals at spatial and temporal scales that were previously impossible. We further suggest that viewing the behaviors of non-human animals in terms of the physical exercise performed will allow us to fully take advantage of these technological advances, draw from knowledge and conceptual frameworks already in use by human exercise physiologists, and identify key traits that constrain performance and generate variation in performance among individuals. It is our hope that, by highlighting mechanisms of behavior and performance, the articles in this issue will spur on further synergies between physiologists and ecologists, to take advantage of emerging cross-disciplinary perspectives and technologies

Predator mediated selection and the impact of developmental stage on viability in wood frog tadpoles (Rana sylvatica)

<p>Abstract</p> <p>Background</p> <p>Complex life histories require adaptation of a single organism for multiple ecological niches. Transitions between life stages, however, may expose individuals to an increased risk of mortality, as the process of metamorphosis typically includes developmental stages that function relatively poorly in both the pre- and post-metamorphic habitat. We studied predator-mediated selection on tadpoles of the wood frog, <it>Rana sylvatica</it>, to identify this hypothesized period of differential predation risk and estimate its ontogenetic onset. We reared tadpoles in replicated mesocosms in the presence of the larval odonate <it>Anax junius</it>, a known tadpole predator.</p> <p>Results</p> <p>The probability of tadpole survival increased with increasing age and size, but declined steeply at the point in development where hind limbs began to erupt from the body wall. Selection gradient analyses indicate that natural selection favored tadpoles with short, deep tail fins. Tadpoles resorb their tails as they progress toward metamorphosis, which may have led to the observed decrease in survivorship. Path models revealed that selection acted directly on tail morphology, rather than through its indirect influence on swimming performance.</p> <p>Conclusions</p> <p>This is consistent with the hypothesis that tail morphology influences predation rates by reducing the probability a predator strikes the head or body.</p

Preseason Mileage Influences the In-Season Training Effect in Female Cross Country Runners

Purpose: The purpose of this study was to analyze how preseason mileage influences the in-season training effect on maximal oxygen uptake (VO2max) and lactate threshold (LT) in trained NAIA runners. Methods: Eight female distance runners (age 21.2 0.5 y) ran preseason mileage prior to the start of the cross country season. Subjects completed a graded treadmill test to determine VO2max and VO2 at OBLA (VO2 OBLA) at the beginning and end of a 9 week competitive season. Results: Postseason testing revealed VO2max significantly improved (p=0.009), while no significant improvement occurred in VO2 OBLA (p=0.145). Preseason mileage was significantly correlated with % VO2 OBLA (r = -0.711) but not with % VO2max (r = -0.440). Average 6 km performance was correlated with preseason mileage (r = -0.710), preseason VO2max (r = -0.944), preseason VO2 OBLA (r = -0.968), and % VO2 OBLA (r = 0.745). Conclusions: These results indicate how running mileage in the preseason influences the extent to which VO2max and VO2 OBLA change in-season and contributes to 6 km performance

Sexually Antagonistic Selection, Sexual Dimorphism, and the Resolution of Intralocus Sexual Conflict

Males and females share most of their genomes and express many of the same traits, yet the sexes often have markedly different selective optima for these shared traits. This sexually antagonistic (SA) selection generates intralocus sexual conflict that is thought to be resolved through the evolution of sexual dimorphism. However, we currently know little about the prevalence of SA selection, the components of fitness that generate sexual antagonism, or the relationship between sexual dimorphism and current SA selection. We reviewed published studies to address these questions, using 424 selection estimates representing 89 traits from 34 species. Males and females often differed substantially in the direction and magnitude of selection on shared traits, although statistically significant SA selection was relatively uncommon. Sexual selection generated stronger sexual antagonism than fecundity or viability selection, and these individual components of fitness tended to reinforce one another to generate even stronger sexual antagonism for net fitness. Traits exhibiting strong sexual dimorphism exhibited greater SA selection than did weakly dimorphic traits, although this pattern was not significant after we controlled for the inclusion of multiple traits nested within species. Our results suggest that intralocus sexual conflict often may persist despite the evolution of sexual dimorphism

A potential role for restricted intertactical heritability in preventing intralocus conflict

Intralocus sexual conflict, which arises when the same trait has different fitness optima in males and females, reduces population growth rates. Recently, evolutionary biologists have recognized that intralocus conflict can occur between morphs or reproductive tactics within a sex and that intralocus tactical conflict might constrain tactical dimorphism and population growth rates just as intralocus sexual conflict constrains sexual dimorphism and population growth rates. However, research has only recently focused on sexual and tactical intralocus conflict simultaneously, and there is no formal theory connecting the two. We present a graphical model of how tactical and sexual conflict over the same trait could constrain both sexual and tactical dimorphisms. We then use Coho salmon (Oncorhynchus kisutch), an important species currently protected under the Endangered Species Act, to investigate the possibility of simultaneous sexual and tactical conflict. Larger Coho males gain access to females through fighting while smaller males are favored through sneaking tactics, and female reproductive success is positively correlated with length. We tested for antagonistic selection on length at maturity among sexes and tactics and then used parent–offspring regression to calculate sex- and tactic-specific heritabilities to determine whether and where intralocus conflict exists. Selection on length varied in intensity and form among tactics and years. Length was heritable between dams and daughters (h2 ± 95% CI = 0.361 ± 0.252) and between fighter males and their fighter sons (0.867 ± 0.312), but no other heritabilities differed significantly from zero. The lack of intertactical heritabilities in this system, combined with similar selection on length among tactics, suggests the absence of intralocus conflict between sexes and among tactics, allowing for the evolution of sexual and tactical dimorphisms. Our results suggest that Coho salmon populations are unlikely to be constrained by intralocus conflict or artificial selection on male tactic

Parallel shifts in ecology and natural selection in an island lizard

<p>Abstract</p> <p>Background</p> <p>Natural selection is a potent evolutionary force that shapes phenotypic variation to match ecological conditions. However, we know little about the year-to-year consistency of selection, or how inter-annual variation in ecology shapes adaptive landscapes and ultimately adaptive radiations. Here we combine remote sensing data, field experiments, and a four-year study of natural selection to show that changes in vegetation structure associated with a severe drought altered both habitat use and natural selection in the brown anole, <it>Anolis sagrei</it>.</p> <p>Results</p> <p>In natural populations, lizards increased their use of vegetation in wet years and this was correlated with selection on limb length but not body size. By contrast, a die-back of vegetation caused by drought was followed by reduced arboreality, selection on body size, and relaxed selection on limb length. With the return of the rains and recovery of vegetation, selection reverted back to pre-drought pattern of selection acting on limb length but not body size. To test for the impact of vegetation loss on natural selection during the drought, we experimentally removed vegetation on a separate study island in a naturally wet year. The experiment revealed similar inter-annual changes in selection on body size but not limb length.</p> <p>Conclusion</p> <p>Our results illustrate the dynamic nature of ecology driving natural selection on <it>Anolis </it>morphology and emphasize the importance of inter-annual environmental variation in shaping adaptive variation. In addition, results illustrate the utility of using remote sensing data to examine ecology's role in driving natural selection.</p

The social position of adolescents and young adults with chronic digestive disorders

A chronic digestive disorder can be accompanied by -sometimes embarrassing- symptoms and complaints, such as pain, lack of energy, flatulency or incontinence, which can affect the social position of patients. In addition, diet commitments, or worries about toilet facilities can have a serious impact on social activities. The present study was conducted to provide a basis for preventive interventions in order to support young patients in their development with a maximum of equal possibilities in society. Central to this thesis is the impact of being diagnosed with a chronic digestive disorder, such as an inflammatory bowel disease (IBD), chronic liver disease, congenital digestive disorder, coeliac disease or food allergy, on the social position of adolescents and young adults. Secondly, it was aimed to investigate whether the type of disease and disease burden characteristics imply risk factors for possible difficulties in the social position. In addition, the contribution of coping was studied. The study was conducted within a theoretical framework (based on the Disablement process model of Jette and Verbrugge, 1994) which is presented in chapter one. On the basis of this model, the following research questions formed the starting-point of this thesis: 1) Do various chronic digestive disorders, i.e. IBD, chronic liver diseases, congenital digestive disorders, coeliac disease and food allergy, have a negative impact on the social position of adolescents and young adults? Which specific aspects of the social position are negatively affected by a chronic digestive disorder? 2) How can the burden of a chronic digestive disorder in adolescents and young adults be described, in terms of daily manifestations, compared to population controls? 3) Does burden of disease constitutes a risk factor for school performance and leisure activities of adolescents and young adults with chronic digestive disorders? 4) Does burden of disease constitutes a risk factor for the labour market position of young adult patients with chronic digestive disorders? 5) Do coping strategies differ between several diagnostic groups and population controls? Do they differ between various age groups? 6) Does the use of coping strategies contribute to school performance and leisure activities of adolescents and young adults with chronic digestive disorders? In total 758 patients, categorized in five diagnostic groups, and 306 population-based controls in the age of 12 to 24 years participated in the study. Details on the background of this study, on the recruitment procedures for patients and controls and on the measurement methods can be found in chapter one. The research questions are successively studied in the following chapters. In addition, one chapter pays attention to the factor structure of the Coping Inventory for Stressful Situations (CISS-21) because it was used in a younger target group than it originally was developed for. Finally, chapter seven discusses the main results. In this chapter, a strength and weakness analysis of this study is given as well, followed by a summary of the most significant conclusions. The chapter closes with recommendations for physicians, for patients and their parents, as well as for future research

Human-induced morphological shifts in an island lizard

Understanding the evolutionary consequences of anthropogenic change is an emerging topic in evolutionary biology. While highly sensitive species may go extinct in response to anthropogenic habitat alteration, those with broader environmental tolerances may persist and adapt to the changes. Here, we use morphological data from the brown anole (Anolis sagrei), a lizard species that lives in both natural and human-disturbed habitats, to examine the impact of anthropogenic habitat alteration. We find populations inhabiting disturbed habitats were significantly larger in snout-vent length, hindspan, and mass and provide evidence that the observed divergence in hindspan is driven by human-induced changes in habitat structure. Populations were found to be genetically distinct among islands but are not genetically differentiated between habitat types on islands. Thus, the observed pattern of intra-island morphological differences cannot be explained by separate founding populations. Rather, our results are consistent with morphological differences between habitats having arisen in situ on each island. Results underscore the significant impact anthropogenic change may have on evolutionary trajectories of populations that persist in human-altered habitats

Natural Selection on Thermal Performance in a Novel Thermal Environment

Tropical ectotherms are thought to be especially vulnerable to climate change because they are adapted to relatively stable temperature regimes, such that even small increases in environmental temperature may lead to large decreases in physiological performance. One way in which tropical organisms may mitigate the detrimental effects of warming is through evolutionary change in thermal physiology. The speed and magnitude of this response depend, in part, on the strength of climate-driven selection. However, many ectotherms use behavioral adjustments to maintain preferred body temperatures in the face of environmental variation. These behaviors may shelter individuals from natural selection, preventing evolutionary adaptation to changing conditions. Here, we mimic the effects of climate change by experimentally transplanting a population of Anolis sagrei lizards to a novel thermal environment. Transplanted lizards experienced warmer and more thermally variable conditions, which resulted in strong directional selection on thermal performance traits. These same traits were not under selection in a reference population studied in a less thermally stressful environment. Our results indicate that climate change can exert strong natural selection on tropical ectotherms, despite their ability to thermoregulate behaviorally. To the extent that thermal performance traits are heritable, populations may be capable of rapid adaptation to anthropogenic warming

Genetic and Maternal Determinants of Effective Dispersal: The Effect of Sire Genotype and Size at Birth in Side-Blotched Lizards

We assessed genetic factors on progeny dispersal due to sire color morph genotypes in a field pedigree and lab crosses, and we measured maternal effects by studying both natural and experimentally induced egg size variation. Progeny were released into nature upon hatching, but we recorded dispersal distance at maturity, which reflects effective dispersal after viability selection has run its course. Progeny dispersal was significantly affected by sire genotype. Progeny from orange sires dispersed the farthest. Progeny from blue sires dispersed intermediate distances. Progeny from yellow sires were the most philopatric. Sire genotype effects interacted with egg size. In particular, enlarged progeny from orange sires dispersed farther, while enlarged progeny from yellow sires were more philopatric. Progeny from blue sires were unaffected by egg size manipulations. Egg manipulations and natural variation generally had concordant effects indicative of causation. However, asymmetry of gigantization and miniaturization on progeny dispersal from some sire genotypes suggest the involvement of maternal factors besides egg size. Results of laboratory crosses with progeny released into nature confirmed key sire genotype effects and identified additional maternal effects that modulated dispersal as a function of progeny gender. We discuss the adaptive implications of progeny dispersal in the context of male (rock‐paper‐scissors) and female strategies (r‐ and K‐density cycle) that are associated with color morphs