Theodore Garland

University of California, Riverside | UCR · Department of Evolution Ecology and Organismal Biology

Effect sizes are a quantitative measure of the magnitude and direction of a phenomenon. These estimates can be compiled across multiple studies to summarize the weight of evidence for a particular alternative hypothesis, which is generally termed a meta-analysis. A meta-analytic approach allows one to summarize information from a wide array of simi...

A putative male advantage in wayfinding ability is the most widely documented sex difference in human cognition and has also been observed in other animals. The common interpretation, the sex-specific adaptation hypothesis, posits that this male advantage evolved as an adaptive response to sex differences in home range size. A previous study a deca...

For terrestrial locomotion of animals and machines, physical characteristics of the substrate can strongly impact kinematics and performance. Snakes are an especially interesting system for studying substrate effects because their gait depends more on the environment than on their speed. We tested sidewinder rattlesnakes (Crotalus cerastes) on two...

Physical activity is a primary determinant of musculoskeletal health in vertebrates. The amount and intensity of exercise activity can impact bone morphology and density, muscle fiber type, and the material properties of passive elastic tissues such as tendon and ligaments. To further investigate the role of exercise intensity and duration on bone...

Exercise has numerous effects on the musculoskeletal system, including muscle hypertrophy and tendon remodeling. Although exercise is well documented to affect tendon materials properties, the impacts of exercise intensity are less understood. To study the effects of exercise intensity on adult tendon, we used a line of mice artificially selected f...

The movement of limbless terrestrial animals differs fundamentally from that of limbed animals, yet few scaling studies of their locomotor kinematics and morphology are available. We examined scaling and relations of morphology and locomotion in sidewinder rattlesnakes (Crotalus cerastes). During sidewinding locomotion, a snake lifts sections of it...

Three decades ago, interactions between evolutionary biology and physiology gave rise to evolutionary physiology. This caused comparative physiologists to improve their research methods by incorporating evolutionary thinking. Simultaneously, evolutionary biologists began focusing more on physiological mechanisms that may help to explain constraints...

Trade-offs and constraints are inherent to life, and studies of these phenomena play a central role in both organismal and evolutionary biology. Trade-offs can be defined, categorized, and studied in at least six, not mutually exclusive, ways. (1) Allocation constraints are caused by a limited resource (e.g., energy, time, space, essential nutrient...

The endocannabinoid (eCB) system in the gut communicates with the body and brain as part of the homeostatic mechanisms that affect energy balance. Although perhaps best known for its effects on energy intake, the eCB system also regulates voluntary locomotor behavior. Here, we examined gut eCB concentrations in relation to voluntary exercise, speci...

While nursing, mammals progress through critical developmental periods for the cardiovascular, musculoskeletal, and central nervous systems. The suckling period in mammals is therefore especially vulnerable to environmental factors that may affect the “developmental programming” of many complex traits. As a result, various aspects of maternal behav...

Skeletal muscles attach to bone at their origins and insertions, and the interface where tendon meets bone is termed the attachment site or enthesis. Mechanical stresses at the muscle/tendon‐bone interface are proportional to the surface area of the bony attachment sites, such that a larger attachment site will distribute loads over a wider area. M...

Significance This work identifies mechanotransduction mechanisms by which blood flow regulates glycolysis in vascular endothelium. We demonstrate that atheroprotective flow pattern decreases glycolysis, an energy-demanding metabolic process, in endothelium in vitro and in vivo. GCKR, an inhibitor of glycolytic flux, is up-regulated by atheroprotect...

Exercise behavior is under partial genetic control, but it is also affected by numerous environmental factors, potentially including early-life experiences whose effects persist into adulthood. We studied genetic and early-life environmental effects on wheel-running behavior in a mouse model that includes four replicate high runner (HR) lines selec...

Alterations to the gut microbiome caused by changes in diet, consumption of antibiotics, etc., can affect host function. Moreover, perturbation of the microbiome during critical developmental periods potentially have long-lasting impacts on hosts. Using four selectively bred High Runner and four non-selected Control lines of mice, we examined the e...

Compared with other squamates, snakes have received relatively little ecomorphological investigation. We examined morphometric and meristic characters of vipers, in which both sidewinding locomotion and arboreality have evolved multiple times. We used phylogenetic comparative methods that account for intraspecific variation (measurement error model...

Ethologically relevant chemical senses and behavioral habits are likely to coadapt in response to selection. As olfaction is involved in intrinsically motivated behaviors in mice, we hypothesized that selective breeding for a voluntary behavior would enable us to identify novel roles of the chemosensory system. Voluntary wheel running (VWR) is an i...

The maximum amount of oxygen consumed during forced exercise (V̇O2max) sets the upper limit to the effort that can be sustained over relatively long periods and can limit activity levels in nature. Among ectotherms, V̇O2max is primarily affected by body size and body temperature, but it should also coadapt with behavior, ecology, and life history a...

Selection experiments can elucidate the varying course of adaptive changes across generations. We examined the appendicular skeleton of house mice from four replicate High Runner (HR) lines bred for physical activity on wheels and four non‐selected Control (C) lines. HR mice reached apparent selection limits between generations 17 and 27, running ~...

Several observational studies have found that the risk for breast cancer is significantly reduced in persons who engage in greater amounts of physical activity. Additional observational studies of breast cancer survivors indicate that greater physical activity before or after diagnosis associates with reduced disease-specific mortality. However, no...

The biological basis of exercise behavior is increasingly relevant for maintaining healthy lifestyles. Various quantitative genetic studies and selection experiments have conclusively demonstrated substantial heritability for exercise behavior in both humans and laboratory rodents. In the "High Runner" selection experiment, 4 replicate lines of Mus...

Behavioral addictions can come in many forms, including over-eating, gambling, and over-exercising. All addictions share a common mechanism involving activation of the natural reward circuit and reinforcement learning, but the extent to which motivation for natural and drug rewards share similar neurogenetic mechanisms remains unknown. A unique mou...

Diving as a lifestyle has evolved on multiple occasions when air-breathing terrestrial animals invaded the aquatic realm, and diving performance shapes the ecology and behaviour of all air-breathing aquatic taxa, from small insects to great whales. Using the largest dataset yet assembled, we show that maximum dive duration increases predictably wit...

Ethologically relevant chemical senses and behavioral habits are likely to coadapt in response to selection. As olfaction is involved in intrinsically motivated behaviors in mice, we hypothesized that selective breeding for a voluntary behavior would enable us to identify novel roles of the chemosensory system. Voluntary wheel running (VWR) is an i...

Increases in availability of energy‐dense foods and simultaneous reductions in physical activity of Western industrialized societies has created an environment that promotes obesity, but alterations in the gut microbiome may also play a role. As with other organismal characteristics, the microbiome may be influenced by factors experienced early in...

Bone is a hard tissue providing mechanical support to vertebrates and is influenced by both genetic and environmental factors. Stress from mechanical loading causes micro‐fractures in bones, triggering dynamic bone remodeling by shifting the balance of absorption and formation to net formation. Prolonged inactivity can lead to bone dystrophy, which...

The Developmental Origins of Health and Disease hypothesis posits that various factors experienced early in life can predispose individuals to being healthy or unhealthy as adults. For example, children with high birth weight, either by being born to obese mothers or mothers who experience high gestational weight gain during pregnancy, are more lik...

Only half of adults in the United States get the physical activity they need to help prevent certain chronic diseases. Such diseases as cardiovascular disease and diabetes are metabolism‐related and closely tied to insufficient physical activity. The endocannabinoid (EC) system serves many physiological roles, including in the regulation of volunta...

During the suckling period, many mammals progress through numerous developmental milestones, including critical periods of the central nervous system, musculoskeletal system, and cardiovascular system – each an important element of physical activity and exercise capacity. In a novel experimental mouse model, four replicate lines were selectively br...

Skeletal muscles attach to bone at their origins and insertions, and the interface where tendon meets bone is termed the muscle attachment site (or enthesis). Muscle attachment sites function to anchor muscles/tendons to bone and to dissipate stress (force per unit area) resulting from force transmission. Mechanical stresses at the muscle/tendon‐bo...

Ecological factors, such as habitat quality, influence the survival and reproductive success of free-living organisms. Urbanization, including roads, alters native habitat and likely influences physiology, behavior, and ultimately Darwinian fitness. Some effects of roads are clearly negative, such as increased habitat fragmentation and mortality fr...

DNA methylation regulates cell type-specific gene expression. Here, in a transgenic mouse model, we show that deletion of the gene encoding DNA methyltransferase Dnmt3a in hypothalamic AgRP neurons causes a sedentary phenotype characterized by reduced voluntary exercise and increased adiposity. Whole-genome bisulfite sequencing (WGBS) and transcrip...

In male mammals that provide care for their offspring, fatherhood can lead to changes in behavioral, morphological, and physiological traits, some of which might constitute trade-offs. However, relatively little is known about these changes, especially across multiple reproductive bouts, which are expected to magnify differences between fathers and...

California mice (Peromyscus californicus) differ from most other mammals in that they are biparental, genetically monogamous, and (compared with other Peromyscus) relatively large. We evaluated effects of cold acclimation on metabolic rate, exercise performance, and morphology of pair-housed male California mice, as well as modulation of these effe...

Ecophysiology is a relatively recent interdisciplinary field, and although active prior to the 75th anniversary of the American Society of Mammalogists (ASM), it has grown in breadth since then. This growth is in part a result of advances in technology that have reduced the size and improved the portability of key instrumentation, and also made seq...

The comparative method has long been a fundamental exploratory tool in evolutionary biology, but this venerable approach was revolutionized in 1985, when Felsenstein published “Phylogenies and the Comparative Method” in The American Naturalist. This article forced comparative biologists to start thinking phylogenetically when conducting statistical...

By 1950, comparative physiology was an established subfield whose broad agenda included (1) cataloging diversity, (2) using physiological information to reconstruct phylogenetic relationships, (3) elucidating how physiology mediates interactions between organisms and their environments, (4) identifying model systems for studying particular function...

Given challenges of studying skeletal form and function in humans, experimental models of skeletal loading are important for understanding both basic and applied questions of the musculoskeletal and associated physiological systems (e.g., energy balance, metabolism, behavior). Experimental approaches have frequently involved controlled loading, oft...

Mammalian skeletal muscle fibers contain varying amounts of myosin isoforms for slow and fast myosin heavy‐chains, (Types 1, 2A, 2X, 2B,). Muscle fibers containing different isoform profiles typically correlate with variable force, speed, and fatigue resistance. We investigated the isoform profiles of various hindlimb muscles in two lines of mice,...

Individual skeletal morphology is determined by genetic effects and within‐generation phenotypic plasticity in response to mechanical loading. Changes in limb bone morphology associated with locomotor activity through ontogeny and across evolutionary time can provide insight into adaptation in locomotor systems. Here, we investigate the effects of...

Indirect genetic effects (IGEs; the heritable influence of one organism on a conspecific) can affect the evolutionary dynamics of complex traits, including behavior. Voluntary wheel running is an important model system in quantitative genetic studies of behavior, but the possibility of IGEs on wheel running and its components (time spent running an...

Interspecific variation in animal form, function and behaviour is often associated with habitat use, implying co-adaptation. Numerous studies of the 'ecomorphs' of Greater Antillean anoles support this generality, but no other lizard group has shown unambiguous, consistent relationships between limb length and habitat use. We tested for such relati...

Glucocorticoids, a class of metabolic hormones, impact a wide range of traits (e.g., behavior, skeletal growth, muscle maintenance, glucose metabolism), and variation in concentrations of circulating glucocorticoids (such as corticosterone), at the level of natural individual variation, in relation to endocrine disorders, or from exogenous suppleme...

Mouse lines selectively bred for high voluntary wheel-running behavior are helpful models for uncovering gene networks associated with increased motivation for physical activity and other reward-dependent behaviors. The fact that multiple brain regions are hypothesized to contribute to distinct behavior components necessitates the simultaneous stud...

Extended lists of differentially expressed genes and enriched functional categories. Table A. Extended list of genes exhibiting activity line by brain region interaction effect. Table B. Extended list of clusters of Gene Ontology molecular functions, biological processes, and KEGG pathways enriched among genes exhibiting activity line-by-brain regi...

abstract: Behavioral ecologists have hypothesized that among- individual differences in resting metabolic rate (RMR) may predict con- sistent individual differences in mean values for costly behaviors or for behaviors that affect energy intake rate. This hypothesis has empirical support and presently attracts considerable attention, but, notably,...

Dryad data: http://dx.doi.org/10.5061/dryad.jn33140. abstract: q2 Behavioral ecologists have hypothesized that among-individual differences in resting metabolic rate (RMR) may predict consistent individual differences in mean values for costly behaviors or for behaviors that affect energy intake rate. This hypothesis has empirical support and prese...

Muscle pH decreases during exercise, which may impair function. Endurance training typically reduces muscle buffering capacity due to changes in fiber type composition, but existing comparisons of species that vary in activity level are ambiguous. We hypothesized that High Runner (HR) lines of mice from an experiment that breeds for voluntary wheel...

Mitochondrial haplotypes have been associated with human and rodent phenotypes, including nonshivering thermogenesis capacity, learning capability, and disease risk. Although the mammalian mitochondrial D-loop is highly polymorphic, D-loops in laboratory mice are identical, and variation occurs elsewhere mainly between nucleotides 9820 and 9830. Pa...

Physical activity is an important component of energy expenditure, and acute changes in activity can lead to energy imbalances that affect body composition, even under ad libitum food availability. One example of acute increases in physical activity is four replicate, selectively-bred High Runner (HR) lines of mice that voluntarily run ~3-fold more...

Running acts as a natural reward and shares features with other rewarding behaviors, such as eating or taking drugs of abuse. Exercise is even proposed to have addictive properties, as humans and rodents have shown signs of “withdrawal,” including anxiety and depression, after being denied exercise. Conditioned place preference (CPP) is a neuro‐beh...

Mammalian skeletal tissue is aerobic, and has relatively high oxygen demand, presumably a result of the processes of bone modelling and remodeling. These processes are often associated with microfractures accrued from load bearing during locomotion, but they are also pivotal during bone growth and in the deposition/requisition of calcium from bone....

Inter‐specific comparative studies have shown that the size of brain structures is often correlated with behavioral propensities or capabilities. Life experiences can contribute to variation in brain‐behavior associations. For example, studies of rodents and humans have shown that environmental enrichment, exercise, and even video games can change...

We have used selective breeding with house mice to study coadaptation of morphology and physiology with the evolution of high daily levels of voluntary exercise. Here, we compared hindlimb bones and muscle masses from the 11th generation of four replicate High Runner (HR) lines of house mice bred for high levels of voluntary wheel running with four...

Objectives: To use a mouse model to investigate the relationships among the components of the systemic robusticity hypothesis (SRH): voluntary exercise on wheels, spontaneous physical activity (SPA) in cages, growth hormones, and skeletal robusticity, especially cranial vault thickness (CVT). Materials and methods: Fifty female mice from lines a...

Reproduction strongly influences metabolism, morphology and behavior in female mammals. In species in which males provide parental care, reproduction might have similar effects on fathers. We examined effects of an environmental challenge on metabolically important physiological, morphological, and behavioral measures, and determined whether these...

To explore reward substitution in the context of voluntary exercise, female mice from four replicate high-runner (HR) lines (bred for wheel running) and four non-selected control (C) lines were given simultaneous access to wheels and palatable solutions as competing rewards (two doses of saccharin [0.1, 0.2% w/v]; two doses of common artificial swe...

Objectives: Analyses of bone cross-sectional geometry are frequently used by anthropologists and paleontologists to infer the loading histories of past populations. To address some underlying assumptions, we investigated the relative roles of genetics and exercise on bone cross-sectional geometry and bending mechanics in three mouse strains: high...

Purpose: Physical activity unquestionably maintains and improves health; however, physical activity levels globally are low and not rising despite all the resources devoted to this goal. Attention in both the research literature and the public policy domain has focused on social-behavioral factors; however, a growing body of literature suggests th...

Among species of lizards, endurance capacity measured on a motorized treadmill is positively related to daily movement distance and time spent moving, but few studies have addressed such relationships at the level of individual variation within a sex and age category in a single population. Both endurance capacity and home range size show substanti...

Much ecological and evolutionary theory predicts that interspecific interactions often drive phenotypic diversification and that species phenotypes in turn influence species interactions. Several phylogenetic comparative methods have been developed to assess the importance of such processes in nature; however, the statistical properties of these me...

Much ecological and evolutionary theory predicts that interspecific interactions often drive phenotypic diversification and that species phenotypes in turn influence species interactions. Several phylogenetic comparative methods have been developed to assess the importance of such processes in nature; however, the statistical properties of these me...

Selection experiments and experimental evolution (EE) provide unique opportunities to study the genetics of adaptation because the target and intensity of selection are known relatively precisely. In contrast to natural selection, where populations are never strictly "replicated," EE routinely includes replicate lines so that selection signatures -...

Animals are constrained by their abilities and by interactions with environmental factors, such as low ambient temperatures. These constraints range from physical impossibilities to energetic inefficiencies, and may entail trade-offs. Some of the constraints related to locomotion and activity metabolism can be illustrated through allometric compari...

Understanding the origin and maintenance of functionally important subordinate traits is a major goal of evolutionary physiologists and ecomorphologists. Within the confines of a limbless body plan, snakes are diverse in terms of body size and ecology, but we know little about the functional traits that underlie this diversity. We used a phylogenet...

Synopsis: Arnold's 1983 path-analytic paradigm, considering "morphology, performance, and fitness," has been elaborated in several ways. For example, current versions recognize the level of "behavior" (including aspects of motivation) as a filter between performance abilities (only measurable if motivation is maximal) and fitness components. Perfo...

Monitoring marine biodiversity is costly and practical solutions have to be implemented to identify species and their preferred habitats, particularly in this era of rapid global change. Citizen science has proven to be effective and with high potential for monitoring efforts, and has been extensively applied to biodiversity. We have used the citiz...

Postural and kinematic aspects of running may have evolved to support high runner (HR) mice to run approximately threefold farther than control mice. Mice from four replicate HR lines selectively bred for high levels of voluntary wheel running show many differences in locomotor behavior and morphology as compared with four nonselected control (C) l...