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Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2023)

I studied correlated responses to artificial selection for high voluntary wheel-running behavior. Chapter 1 used meta-analysis to summarize comparisons of four replicate High Runner (HR) lines with four non-selected Control (C) lines. Effect sizes from 34 studies demonstrate that HR mice have evolved larger hearts and smaller bodies, and that plateaus in effect sizes for both traits coincide with selection limits for wheel running. Chapter 2 tested whether HR mice would have a higher maximal rate of oxygen consumption during forced exercise (VO2max), a higher basal metabolic rate (BMR), and increases in the size of relevant organs. Although HR mice ran ~3-fold more revolutions/day and had higher VO2max, they did not have a statistically higher BMR nor differ in relative organ masses (heart, lung, liver, kidney, spleen, brain, calf muscle) or hematocrit. Thus, a large evolutionary increase in activity level has not required proportionally large changes in underlying morphological or physiological traits. Chapter 3 examined effects of maternal exercise on maternal care and offspring body composition and activity behavior. HR females ran more than C prior to breeding and before parturition, but not after. When housed with wheels, HR females had reduced maternal care compared to C during days 1-10 after parturition. HR females with wheels had fewer litters survive to weaning than those without wheels, but the opposite occurred for C females. For both HR and C dams with wheels, surviving offspring had delayed development as indicated by eye opening and lean mass at weaning. However, maternal wheel access did not alter offspring adult body mass, activity behavior or reproductive success. Overall, the evolution of high voluntary exercise did not require large changes in underlying physiology (e.g., VO2max, BMR), but morphological traits (e.g., body mass, relative heart mass) may have imposed constraints on the evolution of activity levels in these mice. Moreover, HR mothers differ in behavior and/or resource allocation resources when given the opportunity to exercise, which results in costs to offspring survival. Further research is needed to determine the underlying mechanisms of this apparent trade-off between two important biological drives.

    Cover page: Effects of Genetic Background and Early-Life Exercise on Adult Traits Related to Exercise Behavior, Morphology, and Physiology
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2023)
    Physical activity engagement results in a variety of positive health outcomes, including a reduction in cardiovascular disease risk partially due to eccentric remodeling of the heart. The purpose of this investigation was to determine if four replicate lines of High Runner mice that have been selectively bred for voluntary exercise on wheels have a cardiac phenotype that resembles the outcome of eccentric remodeling. Adult females (average age 55 days) from the 4 High Runner and 4 non-selected control lines were anaesthetized via vaporized isoflurane, then echocardiographic images were collected and analyzed for structural and functional differences. High Runner mice in general had lower ejection fractions compared to control mice lines (2-tailed p ​= ​0.023 6) and tended to have thicker walls of the anterior portion of the left ventricle (p ​= ​0.065). However, a subset of the High Runner individuals, termed mini-muscle mice, had greater ejection fraction (p ​= ​0.000 6), fractional shortening percentage (p ​< ​0.000 1), and ventricular mass at dissection (p ​< ​0.002 7 with body mass as a covariate) compared to non-mini muscle mice. Mice from replicate lines bred for high voluntary exercise did not all have inherent positive cardiac functional or structural characteristics, although a genetically unique subset of mini-muscle individuals did have greater functional cardiac characteristics, which in conjunction with their previously described peripheral aerobic enhancements (e.g., increased capillarity) would partially account for their increased V˙ O2max.
      Cover page: Selectively breeding for high voluntary physical activity in female mice does not bestow inherent characteristics that resemble eccentric remodeling of the heart, but the mini-muscle phenotype does.
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2022)
      The gut microbiome can affect various aspects of both behavior and physiology, including exercise ability, but effects on voluntary exercise have rarely been studied. We studied females from a selection experiment in which 4 replicate High Runner (HR) lines of mice are bred for voluntary exercise and compared with 4 non-selected control (C) lines. HR and C mice differ in several traits that likely interact with the gut microbiome, including higher daily running distance, body temperatures when running, spontaneous physical activity when housed without wheels, and food consumption. After two weeks of wheel access to reach a stable plateau in daily running, mice were administered broad-spectrum antibiotics for 10 days. Antibiotic treatment caused a significant reduction in daily wheel-running distance in the HR mice (-21%) but not in the C mice. Antibiotics did not affect body mass or food consumption in either HR or C mice, and we did not observe sickness behavior. Wheel running by HR mice did not recover during the 12 days following cessation of antibiotics. The decreased wheel-running in HR but not C mice, with no apparent negative side effects of antibiotics, suggests that the HR microbiome is an important component of their high-running phenotype.
        Cover page: Oral antibiotics reduce voluntary exercise behavior in athletic mice.
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