Stable isotopes reveal sex- and context-dependent amino acid routing in green anole lizards (Anolis carolinensis).

Allocation of acquired resources to phenotypic traits is affected by resource availability and current selective context. While differential investment in traits is well documented, the mechanisms driving investment at lower levels of biological organization, which are not directly related to fitness, remain poorly understood. We supplemented adult male and female Anolis carolinensis lizards with an isotopically labelled essential amino acid (13C-leucine) to track routing in four tissues (muscle, liver, gonads and spleen) under different combinations of resource availability (high- and low-calorie diets) and exercise training (sprint training and endurance capacity).

Sex-specific effects of immune challenges on green anole lizard metabolism.

Immune responses can increase survival, but they can also incur a variety of costs that may lead to phenotypic trade-offs. The nature of trade-offs between immune activity and other components of the phenotype can vary and depend on the type and magnitude of immune challenge, as well as the energetic costs of simultaneously expressing other traits. There may also be sex-specific differences in both immune activity and trade-offs, particularly with regard to energy expenditure that might differ between males and females during the breeding season.

How does mitochondria function contribute to aerobic performance enhancement in lizards?

Aerobic exercise typically enhances endurance across vertebrates so that chronically high energy demands can be met. Some known mechanisms of doing this include increases in red blood cell numbers, angiogenesis, muscle fiber adaptions, mitochondria biogenesis, and changes to cellular metabolism and oxidative phosphorylation. We used green anole lizards () to test for an effect of aerobic exercise on metabolism, mitochondria densities, and mitochondrial function.

Sprint training interacts with body mass to affect hepatic insulin-like growth factor expression in female green anoles (Anolis carolinensis).

Locomotor performance is a key predictor of fitness in many animal species. As such, locomotion integrates the output of a number of morphological, physiological, and molecular levels of organization, yet relatively little is known regarding the major molecular pathways that bolster locomotor performance. One potentially relevant pathway is the insulin and insulin-like signaling (IIS) network, a significant regulator of physiological processes such as reproduction, growth, and metabolism.

Conserved and convergent mechanisms underlying performance-life-history trade-offs.

Phenotypic trade-offs are inevitable in nature, but the mechanisms driving them are poorly understood. Movement and oxygen are essential to all animals, and as such, the common ancestor to all living animals passed on mechanisms to acquire oxygen and contract muscle, sometimes at the expense of other activities or expression of traits. Nevertheless, convergent pathways have also evolved to deal with critical trade-offs that are necessary to survive ubiquitous environmental challenges.

Immune activation affects whole-organism performance in male but not female green anole lizards (Anolis carolinensis).

Immune responses are intuitively beneficial, but they can incur a variety of costs, many of which are poorly understood. The nature and extent of trade-offs between immune activity and other components of the integrated phenotype can vary, and depend on the type of immune challenge, as well as the energetic costs of simultaneously expressing other traits. There may also be sex differences in both immune activity and immunity-induced trade-offs, particularly in the case of trade-offs involving functional traits such as whole-organism performance capacities that might be of different fitness value to males and females.

Life history and environment predict variation in testosterone across vertebrates.

Endocrine systems act as key intermediaries between organisms and their environments. This interaction leads to high variability in hormone levels, but we know little about the ecological factors that influence this variation within and across major vertebrate groups. We study this topic by assessing how various social and environmental dynamics influence testosterone levels across the entire vertebrate tree of life.

Endurance and sprint training affect immune function differently in green anole lizards ().

Limited resources must be partitioned among traits that enhance fitness. Although survival-related traits often trade off with reproduction, survival-related traits themselves may trade off with each other under energy limitations. Whole-organism performance and the immune system both enhance survival, yet are costly, but it is unclear how the two might trade off with each other under energy-limited conditions.

Baseline and stress-induced corticosterone levels across birds and reptiles do not reflect urbanization levels.

Rates of human-induced environmental change continue increasing with human population size, potentially altering animal physiology and negatively affecting wildlife. Researchers often use glucocorticoid concentrations (hormones that can be associated with stressors) to gauge the impact of anthropogenic factors (e.g.

Sprint speed is unaffected by dietary manipulation in trained male Anolis carolinensis lizards.

Performance traits are energetically costly, and their expression and use can drive trade-offs with other energetically costly life-history traits. However, different performance traits incur distinct costs and may be sensitive to both resource limitation and to the types of resources that are accrued. Protein is likely to be especially important for supporting burst performance traits such as sprint speed, but the effect of varying diet composition on sprint training in lizards, an emerging model system for exercise training, is unknown.

Corticosterone in Lizard Egg Yolk Is Reduced by Maternal Diet Restriction but Unaltered by Maternal Exercise.

When females face adverse environmental conditions, physiological changes, such as elevated corticosterone levels, to cope with the stressors may also impact their offspring. Such maternal effects are often considered adaptive and may "prime" the offspring for the same adverse environment, but maternal corticosterone levels do not always match that of the eggs produced. We examined how diet restriction and increased locomotor activity, via exercise training, affected steroid hormone levels of female green anole lizards, as well as the hormone levels in the yolk of their eggs.

Macroevolutionary Patterning in Glucocorticoids Suggests Different Selective Pressures Shape Baseline and Stress-Induced Levels.

Glucocorticoid (GC) hormones are important phenotypic mediators across vertebrates, but their circulating concentrations can vary markedly. Here we investigate macroevolutionary patterning in GC levels across tetrapods by testing seven specific hypotheses about GC variation and evaluating whether the supported hypotheses reveal consistent patterns in GC evolution. If selection generally favors the "supportive" role of GCs in responding effectively to challenges, then baseline and/or stress-induced GCs may be higher in challenging contexts.

Experimentally enhanced performance decreases survival in nature.

Superior locomotor performance confers advantages in terms of male combat success, survival and fitness in a variety of organisms. In humans, investment in increased performance via the exercise response is also associated with numerous health benefits, and aerobic capacity is an important predictor of longevity. Although the response to exercise is conserved across vertebrates, no studies have tested whether non-human animals that invest in increased athletic performance through exercise realize a survival advantage in nature.

Leptin ameliorates the immunity, but not reproduction, trade-off with endurance in lizards.

Life-history trade-offs result from allocation of limited energetic resources to particular traits at the expense of others. When resources are scarce, some traits will take priority over others in the degree of their expression. For example, the current reproduction may be sacrificed to enhance survival.

Illuminating Endocrine Evolution: The Power and Potential of Large-Scale Comparative Analyses.

Hormones are central mediators of genotype-phenotype and organism-environment interactions. Despite these important functions, the role of selection in shaping hormonal mediators of phenotype remains poorly understood. Thanks to decades of work by endocrinologists, circulating hormone levels have been measured in a diversity of organisms.

Species-Specific Means and Within-Species Variance in Glucocorticoid Hormones and Speciation Rates in Birds.

At macroevolutionary scales, stress physiology may have consequences for species diversification and subspecies richness. Populations that exploit new resources or undergo range expansion should cope with new environmental challenges, which could favor higher mean stress responses. Within-species variation in the stress response may also play a role in mediating the speciation process: in species with broad variation, there will always be some individuals that can tolerate an unpredictable environment, whereas in species with narrow variation there will be fewer individuals that are able to thrive in a new ecological niche.

Metabolic Scaling of Stress Hormones in Vertebrates.

Glucocorticoids (GCs) are stress hormones that can strongly influence physiology, behavior, and an organism's ability to cope with environmental change. Despite their importance, and the wealth of studies that have sought to understand how and why GC concentrations vary within species, we do not have a clear understanding of how circulating GC levels vary within and across the major vertebrate clades. New research has proposed that much interspecific variation in GC concentrations can be explained by variation in metabolism and body mass.

Standing Variation and the Capacity for Change: Are Endocrine Phenotypes More Variable Than Other Traits?

Circulating steroid hormone levels exhibit high variation both within and between individuals, leading some to hypothesize that these phenotypes are more variable than other morphological, physiological, and behavioral traits. This should have profound implications for the evolution of steroid signaling systems, but few studies have examined how endocrine variation compares to that of other traits or differs among populations. Here we provide such an analysis by first exploring how variation in three measures of corticosterone (CORT)-baseline, stress-induced, and post-dexamethasone injection-compares to variation in key traits characterizing morphology (wing length, mass), physiology (reactive oxygen metabolite concentration [d-ROMs] and antioxidant capacity), and behavior (provisioning rate) in two populations of tree swallow (Tachycineta bicolor).

Do Seasonal Glucocorticoid Changes Depend on Reproductive Investment? A Comparative Approach in Birds.

Animals go through different life history stages such as reproduction, moult, or migration, of which some are more energy-demanding than others. Baseline concentrations of glucocorticoid hormones increase during moderate, predictable challenges and thus are expected to be higher when seasonal energy demands increase, such as during reproduction. By contrast, stress-induced glucocorticoids prioritize a survival mode that includes reproductive inhibition.

HormoneBase, a population-level database of steroid hormone levels across vertebrates.

Hormones are central regulators of organismal function and flexibility that mediate a diversity of phenotypic traits from early development through senescence. Yet despite these important roles, basic questions about how and why hormone systems vary within and across species remain unanswered. Here we describe HormoneBase, a database of circulating steroid hormone levels and their variation across vertebrates.

Energetic costs of performance in trained and untrained lizards.

The energetic costs of performance constitute a non-trivial component of animals' daily energetic budgets. However, we currently lack an understanding of how those costs are partitioned among the various stages of performance development, maintenance and production. We manipulated individual investment in performance by training lizards for endurance or sprinting ability.

Predicting Life-History Trade-Offs with Whole-Organism Performance.

Whole-organism performance traits are key intermediaries between the organism and the environment. Because performance traits are energetically costly to both build and maintain, performance will compete with other life-history traits over a limited pool of acquired energetic resources at any given time, potentially leading to trade-offs in performance expression. Although these trade-offs can have important implications for organismal fitness we currently lack a conceptual framework for predicting both where trade-offs might be expected, and which traits may be especially prone to trade-offs with other fitness-related life-history traits.

Introduction to the Symposium: Integrative Life-History of Whole-Organism Performance.

A strong case can be made for whole-organism performance traits (i.e., dynamic, ecologically relevant traits whose expression is shaped by underlying morphological factors) as being the ultimate integrative traits.

How Do We Measure the Cost of Whole-Organism Performance Traits?

Whole-organism performance traits, such as maximal speed and endurance capacity are undoubtedly costly, but we know little about how or when all of the costs associated with performance are paid to individuals or how to measure them. To understand how performance traits might be involved in trade-offs with other life-history traits it is critical to determine the development, production, and maintenance costs of performance traits, as well as how each of these changes with increased or decreased use of the performance trait. We discuss the advantages and disadvantages of several potential phenotypic measures of dynamic whole-organism performance that may be used in life-history studies, including direct performance measures; metabolic rates; ecological cost of transport; and changes in metabolic rate after training.

Exercise training reveals trade-offs between endurance performance and immune function, but does not influence growth, in juvenile lizards.

Acquired energetic resources allocated to a particular trait cannot then be re-allocated to a different trait. This often results in a trade-off between survival and reproduction for the adults of many species, but such a trade-off may be manifested differently in juveniles not yet capable of reproduction. Whereas adults may allocate resources to current and/or future reproduction, juveniles can only allocate to future reproduction.