Papers by Theodore Garland
An Introduction to Evolutionary Physiology, with an Example of Experimental Evolution
The FASEB Journal
By 1950, comparative physiology was an established subfield whose broad agenda included (1) catal... more 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 functions, and (5) using kind of organism as a pseudo‐experimental variable. Physiological ecology developed somewhat later, with an emphasis on the third goal. Both fields always had an evolutionary component, but only in the late 1970s did evolutionary physiology arise, borrowing rigorous inferential approaches from evolutionary biology and population/quantitative genetics. This newer subfield uses a range of approaches to ask whether the way organisms work influences the ways they evolve, and if so, how. Approaches include phylogenetically informed comparative studies, measurement of selection in wild populations, quantitative genetic analysis ...
Creation of a Novel Inbred Mouse Model for High Activity with a Small Muscle Phenotype
The FASEB Journal
Given challenges of studying skeletal form and function in humans, experimental models of skeleta... more 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, often axial loads placed on the ulna or tibia. Although appealing in allowing for precise estimates of stress and strain, these approaches often generate extremely high tissue strains, resulting in potentially pathological overload. Conversely, natural models of locomotor loading result in unknown levels of tissue strain but benefit by representing behaviors that animals will perform in life. Voluntary locomotion via an activity wheel can be used to explore the behavioral and physiological challenges of long‐term voluntary exercise. Furthermore, because activity is a heritable trait, it can be selected upon to gradually increase across genera...
The quantitative genetics of a complex trait under continuous directional selection
The FASEB Journal
We analyzed data from a long‐term artificial selection experiment that includes 4 lines of mice b... more We analyzed data from a long‐term artificial selection experiment that includes 4 lines of mice bred for high voluntary wheel running (HR) and 4 non‐selected control (C) lines. The HR lines reached a selection limit at generation ~16, running ~3‐fold more revolutions/day than C lines. In addition, wheel running varied across generations in an apparently cyclical fashion in both HR and C. We used the first 25 generations to estimate quantitative genetic parameters before, during, and after the selection limit was reached. We used ASReml‐R to apply the “animal model”, a linear mixed‐model that uses all the information on the coefficients of co‐ancestry among individuals in a pedigree. Our preliminary results indicate additive genetic variance (VA) was not eliminated in HR lines after the limit was reached. However, the selection regime led to a negative covariance between VA and maternal genetic variance (VM), which could maintain VA in the selected trait and potentially explain the p...
Comparison of Morphology and Bending Mechanics of Femora in Response to Chronic Exercise in Three Strains of Mice
The FASEB Journal
Analyses of bone cross‐sectional geometry are frequently used to predict the loading histories of... more Analyses of bone cross‐sectional geometry are frequently used to predict the loading histories of past populations. We investigated the interplay between genetic background and exercise, as well as the relationship between bone cross‐sectional geometry and bending mechanics, in three mouse strains: high bone density (C3H/He), low bone density (C57BL/6), and a high‐runner strain homozygous for the Myh4Minimsc allele (MM). Each strain was divided into exercise (wheel) or control (no wheel) treatment groups. After seven weeks, morphometric and mechanical loading analyses were conducted on dissected femora. Comparisons of exercise versus control treatments revealed no significant differences within any strain, although exercising MM mice ran significantly more than their C3H/He and C57BL/6 counterparts (P < 0.001). Thus, predictions that exercise would alter bone phenotype were not supported in this sample. Results of cross‐sectional geometry predicted that MM femora would be most re...
Research Square (Research Square), Dec 16, 2021
Effects of Selective Breeding, Voluntary Exercise, and Sex on Endocannabinoid Levels in the Mouse Small-Intestinal Epithelium
Physiology & Behavior, Mar 1, 2022
The endocannabinoid (eCB) system in the gut communicates with the body and brain as part of the h... more 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, specifically in mice selectively bred for high voluntary wheel running behavior. We measured gut eCBs in four replicate non-selected Control (C) lines and four replicate lines of High Runner (HR) mice that had been selectively bred for 74 generations based on the average number of wheel revolutions on days 5 and 6 of a 6-day period of wheel access when young adults. On average, mice from HR lines run voluntarily on wheels ∼3-fold more than C mice on a daily basis. A recent study showed that circulating levels of primary endocannabinoids 2-arachidonoyl-sn-glycerol (2-AG) and anandamide (AEA) are altered by six days of wheel access, by acute wheel running, and differ between HR and C mice in sex-specific ways [1]. We hypothesized that eCBs in the upper small-intestinal epithelium (i.e., proximal jejunum), a region firmly implicated in eCB signaling, would differ between HR and C mice (linetype), between the sexes, between mice housed with vs. without wheels for six days, and would covary with amounts of acute running and/or home-cage activity (during the previous 30 minutes). We used the same 192 mice as in Thompson et al. (2017), half males and half females, half HR and half C (all 8 lines), and half either given or not given access to wheels for six days. We assessed the eCBs, 2-AG and AEA, and their analogs docosahexaenoylglycerol (DHG), docosahexaenoylethanolamide (DHEA), and oleoylethanolamide (OEA). Both 2-AG and DHG showed a significant 3-way interaction of linetype, wheel access, and sex. In addition, HR mice had lower concentrations of 2-AG in the small-intestinal epithelium when compared to C mice, which may be functionally related to differences in locomotor activity or to differences in body composition and/or food consumption. Moreover, the amount of home-cage activity during the prior 30 min was a negative predictor of 2-AG and AEA concentrations in mucosa, particularly in the mice with no wheel access. Lastly, 2-AG, but not AEA, was significantly correlated with 2-AG in plasma in the same mice.
Journal of Developmental Origins of Health and Disease, Oct 4, 2022
Fructose (C 6 H 12 O 6) is acutely obesogenic and is a risk factor for hypertension, cardiovascul... more Fructose (C 6 H 12 O 6) is acutely obesogenic and is a risk factor for hypertension, cardiovascular disease, and nonalcoholic fatty liver disease. However, the possible long-lasting effects of earlylife fructose consumption have not been studied. We tested for effects of early-life fructose and/ or wheel access (voluntary exercise) in a line of selectively bred High Runner (HR) mice and a non-selected Control (C) line. Exposures began at weaning and continued for 3 weeks to sexual maturity, followed by a 23-week "washout" period (equivalent to~17 human years). Fructose increased total caloric intake, body mass, and body fat during juvenile exposure, but had no effect on juvenile wheel running and no important lasting effects on adult physical activity or body weight/composition. Interestingly, adult maximal aerobic capacity (VO 2 max) was reduced in mice that had early-life fructose and wheel access. Consistent with previous studies, early-life exercise promoted adult wheel running. In a 3-way interaction, C mice that had earlylife fructose and no wheel access gained body mass in response to 2 weeks of adult wheel access, while all other groups lost mass. Overall, we found some long-lasting positive effects of early-life exercise, but minimal effects of early-life fructose, regardless of the mouse line. Key findings • Early-life exercise has numerous positive effects on adult traits. • Early-life fructose consumption has minimal impacts on adult health. • Exercise acutely protects against obesogenic effects of fructose in juvenile mice. 250 Marcell D. Cadney et al.
The long-lasting shadow of litter size in rodents: litter size is an underreported variable that strongly determines adult physiology
Molecular metabolism, May 1, 2023
PLOS ONE, Nov 30, 2022
Muscle injury can be caused by strenuous exercise, repetitive tasks or external forces. Populatio... more Muscle injury can be caused by strenuous exercise, repetitive tasks or external forces. Populations that have experienced selection for high locomotor activity may have evolutionary adaptations that resist exercise-induced injury and/or enhance the ability to cope with injury. We tested this hypothesis with an experiment in which mice are bred for high voluntary wheel running. Mice from four high runner lines run~three times more daily distance than those from four non-selected control lines. To test recovery from injury by external forces, mice experienced contusion via weight drop on the calf. After injury, running distance and speed were reduced in high runner but not control lines, suggesting that the ability of control mice to run exceeds their motivation. To test effects of injury from exercise, mice were housed with/without wheels for six days, then trunk blood was collected and muscles evaluated for injury and regeneration. Both high runner and control mice with wheels had increased histological indicators of injury in the soleus, and increased indicators of regeneration in the plantaris. High runner mice had relatively more central nuclei (regeneration indicator) than control in the soleus, regardless of wheel access. The subset of high runner mice with the mini-muscle phenotype (characterized by greatly reduced muscle mass and type IIb fibers) had lower plasma creatine kinase (indicator of muscle injury), more markers of injury in the deep gastrocnemius, and more markers of regeneration in the deep and superficial gastrocnemius than normal-muscled individuals. Contrary to our expectations, high runner mice were not more resistant to either type of injury.
Carolina Digital Repository (University of North Carolina at Chapel Hill), 2011
Bone strength is influenced by many properties intrinsic to bone, including its mass, geometry, a... more Bone strength is influenced by many properties intrinsic to bone, including its mass, geometry, and mineralization. To further advance our understanding of the genetic basis of bone strengthrelated traits, we utilized a large (N=815), moderately (G 4) advanced intercross line (AIL) of mice derived from a high-runner selection line (HR) and the C57BL/6J inbred strain. In total, 16 quantitative trait loci (QTL) were identified that affected areal bone mineral density (aBMD) and femoral length and width. Four significant (P<0.05) and one suggestive (P<0.10) QTL were identified for three aBMD measurements: total body, vertebral and femoral. A QTL on Chromosome (Chr.) 3 influenced all three aBMD measures, while the other four QTL were unique to a single measure. A total of 10 significant and one suggestive QTL were identified for femoral length (FL) and two measures of femoral width, anterior-posterior (AP) and medial-lateral (ML). FL QTL were distinct from loci affecting AP and ML width, and of the seven AP QTL, only three affected ML. A QTL on Chr. 8 that explained 7.1% and 4.0% of the variance in AP and ML, respectively, was mapped to a six megabase (Mb) region harboring 12 protein-coding genes. The pattern of haplotype diversity across the QTL region and expression profiles of QTL genes, suggested that of the 12, cadherin 11 (Cdh11) was most likely the causal gene. These findings, when combined with existing data from gene knockouts, identify Cdh11 as a strong candidate gene within which genetic variation may affect bone morphology.
Early Post‐Natal Maternal Effects on Voluntary Exercise, Maximal Aerobic Capacity, and Associated Traits in Mice
The FASEB Journal, Apr 1, 2020
During the suckling period, many mammals progress through numerous developmental milestones, incl... more 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 bred for ~90 generations for high voluntary wheel‐running behavior (high‐runner; HR) while four non‐selected Control (C) lines were also maintained. As a result of selection, HR mice run approximately 3‐fold the distances of C mice on a daily basis. Various other physiological and behavioral differences have also evolved in the HR lines, including higher maximal oxygen consumption (VO2max). The aim of the present study was to assess the role of the maternal environment during the birth‐weaning period in the expression of the many differences between HR and C lines using a cross‐fostering paradigm. Cross‐fostering HR mice to C dams (and vice versa) at birth and until weaning allowed us to determine the relative contribution of genetic and early environmental factors in shaping the HR phenotype. Mice were weaned three weeks after birth, housed in same‐sex cages of four, and adult testing began at approximately six weeks of age with measurement of VO2max, daily wheel running over a six‐day period, food consumption, home‐cage activity, body fat composition, and organ masses following dissection. As expected, HR mice ran approximately ~3‐fold more revolutions/day on wheels than their C counterparts. Preliminary analyses show that rearing by an HR dam has a negative effect on adult wheel running in females. This result suggests that the maternal environment provided by HR dams during the suckling period may play a role in the selection limit observed in HR lines.Support or Funding InformationNSF GRFP
Western diet increases wheel running in mice selectively bred for high voluntary wheel running
The FASEB Journal, Apr 1, 2010
Mice from a long-term selective breeding experiment for high voluntary wheel running offer a uniq... more Mice from a long-term selective breeding experiment for high voluntary wheel running offer a unique model to examine the contributions of genetic and environmental factors in determining the aspects of behavior and metabolism relevant to body-weight regulation and obesity. Starting with generation 16 and continuing through to generation 52, mice from the four replicate high runner (HR) lines have run 2.5-3-fold more revolutions per day as compared with four non-selected control (C) lines, but the nature of this apparent selection limit is not understood. We hypothesized that it might involve the availability of dietary lipids. Wheel running, food consumption (Teklad Rodent Diet (W) 8604, 14% kJ from fat; or Harlan Teklad TD.88137 Western Diet (WD), 42% kJ from fat) and body mass were measured over 1-2-week intervals in 100 males for 2 months starting 3 days after weaning. WD was obesogenic for both HR and C, significantly increasing both body mass and retroperitoneal fat pad mass, the latter even when controlling statistically for wheel-running distance and caloric intake. The HR mice had significantly less fat than C mice, explainable statistically by their greater running distance. On adjusting for body mass, HR mice showed higher caloric intake than C mice, also explainable by their higher running. Accounting for body mass and running, WD initially caused increased caloric intake in both HR and C, but this effect was reversed during the last four weeks of the study. Western diet had little or no effect on wheel running in C mice, but increased revolutions per day by as much as 75% in HR mice, mainly through increased time spent running. The remarkable stimulation of wheel running by WD in HR mice may involve fuel usage during prolonged endurance exercise and/or direct behavioral effects on motivation. Their unique behavioral responses to WD may render HR mice an important model for understanding the control of voluntary activity levels.
American Journal of Physical Anthropology, Jun 14, 2018
We welcome Ruff, Warden, and Karlson's letter in response to our recent (Peacock et al., 2018) an... more We welcome Ruff, Warden, and Karlson's letter in response to our recent (Peacock et al., 2018) analysis of the relative differences in skeletal traits among and within three strains of mice. Our goal was to highlight the challenges of interpreting skeletal phenotypes as primarily the result of habitual physical activity. We found higher prevalence of differences in skeletal phenotypes among strains of mice than we found resulting from chronic voluntary exercise within strains. Ruff and colleagues disagree with our work from both philosophical and analytic standpoints, and we respond to their concerns here. Ruff et al. criticize our choice of mouse strains (Myh4 Minimsc , C57BL/6NHsd, and C3H/HENHsd; hereafter MM, C57, and C3H) to test for the relative effects of seven weeks of voluntary exercise on skeletal phenotypes. They make several erroneous statements regarding the nature of the strains we chose for our study. The partially
General and Comparative Endocrinology, Aug 1, 2020
Ecological factors, such as habitat quality, influence the survival and reproductive success of f... more 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 from vehicle collision. However, roads can also have positive effects, such as decreasing predator density and increased vegetation cover, particularly in xeric habitats due to increased water runoff. Glucocorticoids are metabolic hormones that reflect baseline metabolic needs, increase in response to acute challenges, and may mediate endogenous resource trade-offs between survival and reproduction. Here we examined circulating concentrations of corticosterone (baseline and stress-induced) in desert iguanas (Dipsosaurus dorsalis) in relation to the distance from a major anthropogenic disturbance, a high-traffic road in Palm Springs, CA. Additionally, we analyzed body condition and population density as additional predictors of glucocorticoid physiology. Surprisingly, we found lower baseline CORT levels closer to the road, but no effect of distance from road on stress-induced CORT or stress responsiveness (difference between baseline and stress-induced concentrations). Both population density and body condition were negative predictors of baseline CORT, stressinduced CORT, and stress responsiveness. Given the known effect of roads to increase runoff and vegetation density, increased water availability may improve available forage and shade, which may then increase the carrying capacity of the habitat and minimize metabolic challenges for this herbivorous lizard. However, it is important to recognize that surfaces covered by asphalt are not usable habitat for iguanas, likely resulting in a net habitat loss.
Carolina Digital Repository (University of North Carolina at Chapel Hill), 2010
Exercise is essential for health, yet the amount, duration, and intensity that individuals engage... more Exercise is essential for health, yet the amount, duration, and intensity that individuals engage in is strikingly variable, even under prescription. Our focus was to identify the locations and effects of quantitative trait loci (QTL) controlling genetic predisposition for exercise-related traits utilizing a large advanced intercross line (AIL) of mice. This AIL (G 4) population originated from a reciprocal cross between mice with genetic propensity for increased voluntary exercise (HR, selectively bred for increased wheel running) and the inbred strain C57BL/6J. After adjusting for family structure, we detected 32 significant and 13 suggestive QTL representing both daily running traits (distance, duration, average speed, and maximum speed) and the mean of these traits on days 5 and 6 (the selection criteria for HR) of a 6-day test conducted at 8 weeks of age, with many colocalizing to similar genomic regions. Additionally, 7 significant and 5 suggestive QTL were observed for the slope and intercept of a linear regression across all 6 days of running, some representing a combination of the daily traits. We also observed 2 significant and 2 suggestive QTL for body mass prior to exercise. These results, using a well-defined animal model, reinforce a genetic basis for the predisposition to engage in voluntary exercise, dissect this predisposition into daily segments across a continuous time period, and present unique QTL that may provide insight into the initiation, continuation, and temporal pattern of voluntary activity in mammals.
Muscle Fiber‐type Differences in Mice Selected for Wheel Running Behavior
The FASEB Journal, Apr 1, 2019
Mammalian skeletal muscle fibers contain varying amounts of myosin isoforms for slow and fast myo... more 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, one of which has been undergoing laboratory selection for high wheel‐running behavior for over 80 generations. We hypothesized that the selected line would typically have the most type 1 or type 2a myosin. This isoform is most often expressed in muscle with higher oxidative capacity and therefore greater fatigue resistance. We collected lower leg muscles including the quadriceps, soleus, medial and lateral gastrocnemius, and plantaris from the breeding pairs of generation 80 from replicated selected and control lines.Some data were previously reported from generations collected over a decade ago, but many muscles were not included, and we wished to see if further changes to the isoform profiles have arisen. SDS PAGE and densitometry were used to quantify the myosin isoforms.Preliminary analysis using densitometry shows that the leg muscles of high‐running mice had a higher concentration of type 1 myosin, or in other cases, a shift towards slower type 2 fibers (i.e. 2x to 2a). The findings were highly muscle‐specific, and indicate shifts in muscle protein expression has resulted from selection.Our new catalog of isoform profiles will serve as a baseline for comparison of two future studies – one following the development and subsequent senescence of muscle function with aging, and the second determining the effect of exercise activity on both selected and control lines.With the aging study we hope to identify whether activity during the lifetime is as important and genetic factors in preventing the decline of muscle performance with age. For the exercise study, we hope to determine the influence of genetics on shaping exercise performance for individuals which descend from sedentary or active lines. All of these data address long‐standing nature vs nurture debates, but also bear on human clinical muscle disease, aging, and activity.Support or Funding InformationThis research was supported by California State University, Long Beach and the National Institute of General Medical Sciences of the National Institutes of Health under Award Numbers; 8UL1GM118979‐02; 8TL4GM118980‐02; 8RL5GM118978‐02. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We would also like to thank Dr. Theodore Garland from University of California, Riverside and Dr. Angela Horner from California State University, San Bernardino.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
The Effect of Selective Breeding for High Voluntary Wheel‐Running Behavior on Femoral Nutrient Canal Abundance and Size
The FASEB Journal, Apr 1, 2018
Selective breeding of mice for high voluntary exercise alters adaptive plasticity of metabolic phenotypes in skeletal muscle
The FASEB Journal, Apr 1, 2012
The response to selection on behavior necessarily entails associated changes in lower‐level (subo... more The response to selection on behavior necessarily entails associated changes in lower‐level (subordinate) traits. We studied mice from 4 replicate lines that had been selectively bred for high levels of voluntary exercise (High Runner or HR) that run ~3‐fold more wheel revolutions/day than those from 4 non‐selected control (C) lines, and have evolved higher baseline endurance and VO2max. We examined hindlimb skeletal muscle metabolic capacity in mice housed with or without wheel access for 8 weeks. Triceps surae muscles were assayed at 37C for Vmax of hexokinase (HK), citrate synthase (CS), carnitine palmitoyl‐transferase (CPT), and β‐hydroxyacyl‐CoA dehydrogenase (HAD). Wheel access increased heart ventricle mass in both HR and C lines, but only HR showed increased enzyme activities as well as higher phosphorylation of 5ˈ‐AMP‐activated protein kinase. Analysis of wheel‐access groups indicated the greater training effect in HR could be explained statistically by their greater wheel running for ventricle mass, CS, and HAD, but for HK and CPT, HR mice had greater adaptive plasticity of the response to voluntary exercise. Thus, HR do not have inherent baseline differences in metabolic capacity, but they have evolved greater adaptive plasticity for some traits. Supported by NSF IOB‐0543429 and IOS‐1121273 to TG.
Lower-level predictors and behavioral correlates of maximal aerobic capacity and sprint speed among individual lizards
The Journal of Experimental Biology, Mar 1, 2023
ABSTRACT The standard paradigm of organismal biology views lower-level traits (e.g. aspects of ph... more ABSTRACT The standard paradigm of organismal biology views lower-level traits (e.g. aspects of physiology) as determining organismal performance ability (e.g. maximal sprint speed), which in turn constrains behavior (e.g. social interactions). However, few studies have simultaneously examined all three levels of organization. We used focal observations to record movement behaviors and push-up displays in the field for adult male Sceloporus occidentalis lizards during the breeding season. We then captured animals, measured aspects of their physiology, morphology and performance, and counted ectoparasites and endoparasites as potential predictors of sprint speed and maximal oxygen consumption (V̇O2,max). Field behaviors were statistically repeatable, but not strongly so. Sprint speed and V̇O2,max were repeatable using residuals from regressions on body mass (speed: r=0.70; V̇O2,max: r=0.88). Both calf [standardized partial regression (path) coefficient B=0.53] and thigh [B=−0.37] muscle mass (as residuals from regressions on body mass) were significant predictors of sprint speed; hemoglobin concentration (B=0.42) was a predictor of V̇O2,max. In turn, V̇O2,max predicted the maximum number of four-legged push-ups per bout (B=0.39). In path analysis, log likelihood ratio tests indicated no direct paths from lower-level traits to behavior, supporting the idea that morphology, in the broad sense, only affects behavior indirectly through measures of performance. Our results show that inter-individual variation in field behaviors can be related to performance ability, which in turn reflect differences in morphology and physiology, although not parasite load. Given the low repeatability of field behaviors, some of the relationships between behavior and performance may be stronger than suggested by our results.
The Journal of Experimental Biology, 2020
Among species of lizards, helodermatids, varanids, and skinks (which are mainly active foragers) ... more Among species of lizards, helodermatids, varanids, and skinks (which are mainly active foragers) have relatively high maximal aerobic capacity during forced exercise (V O2max), whereas viviparous species have relatively low V O2max.
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Papers by Theodore Garland