QUANTITATIVE GENETICS OF SPRINT RUNNING SPEED AND SWIMMING ENDURANCE IN LABORATORY HOUSE MICE (MUS DOMESTICUS)

Effects of high-intensity interval training on gut microbiota profiles in 12 months' old ICR mice

High-intensity interval training (HIT) has been proposed to exert multiple beneficial effects and positively affect gut microbiota, while how HIT would affect gut microbiota profiles in middle-aged mice remain unreported. Male ICR mice (12 months old) were divided into two groups, i.e., control group (CON) and HIT exercise group (HIT) given HIT running with a total of 7 weeks. Fecal content from the gut was collected eventually and gut microbiota were determined via 16S rRNA gene sequencing. Compared with CON group, mice from HIT group exhibited improved gut microbial diversity including increased Shannon index. Compared with the CON group, at the phylum level, the relative abundance of Proteobacteria and TM7 was significantly decreased and increased, respectively, from HIT group. At the genera level, HIT group had significantly increased Dorea and Dehalobacterium, while decreased Candidatus Arthromitus. PICRUSt analysis at level 2 and level 3 of KEGG pathways demonstrated that the cecal microbiota of mice from HIT group had significantly enriched pathways involved in carbohydrate metabolism, signal transduction mechanisms, and transcription, while reduced pathways involved in renal cell carcinoma, Huntington's disease, pathways in cancer, various types of N-glycan biosynthesis, Alzheimer's disease, glycan biosynthesis and metabolism, lipopolysaccharide biosynthesis, cell motility and secretion, and lipopolysaccharide biosynthesis proteins. In conclusion, HIT could dynamically alter gut microbiota profiles in middle-aged mice. How altered gut microbiota profiles could affect the biological functions of HIT need to be further explored.

Evolution of physiological performance capacities and environmental adaptation: insights from high-elevation deer mice (Peromyscus maniculatus)

Analysis of variation in whole-animal performance can shed light on causal connections between specific traits, integrated physiological capacities, and Darwinian fitness. Here, we review and synthesize information on naturally occurring variation in physiological performance capacities and how it relates to environmental adaptation in deer mice (Peromyscus maniculatus). We discuss how evolved changes in aerobic exercise capacity and thermogenic capacity have contributed to adaptation to high elevations. Comparative work on deer mice at high and low elevations has revealed evolved differences in aerobic performance capacities in hypoxia. Highland deer mice have consistently higher aerobic performance capacities under hypoxia relative to lowland natives, consistent with the idea that it is beneficial to have a higher maximal metabolic rate (as measured by the maximal rate of O₂ consumption, VO_2max) in an environment characterized by lower air temperatures and lower O₂ availability. Observed differences in aerobic performance capacities between highland and lowland deer mice stem from changes in numerous subordinate traits that alter the flux capacity of the O₂-transport system, the oxidative capacity of tissue mitochondria, and the relationship between O₂ consumption and ATP synthesis. Many such changes in physiological phenotype are associated with hypoxia-induced changes in gene expression. Research on natural variation in whole-animal performance forms a nexus between physiological ecology and evolutionary biology that requires insight into the natural history of the study species.

Performance trade-offs and ageing in the 'world's greatest athletes'

The mechanistic foundations of performance trade-offs are clear: because body size and shape constrains movement, and muscles vary in strength and fibre type, certain physical traits should act in opposition with others (e.g. sprint versus endurance). Yet performance trade-offs are rarely detected, and traits are often positively correlated. A potential resolution to this conundrum is that within-individual performance trade-offs can be masked by among-individual variation in 'quality'. Although there is a current debate on how to unambiguously define and account for quality, no previous studies have partitioned trait correlations at the within- and among-individual levels. Here, we evaluate performance trade-offs among and within 1369 elite athletes that performed in a total of 6418 combined-events competitions (decathlon and heptathlon). Controlling for age, experience and wind conditions, we detected strong trade-offs between groups of functionally similar events (throwing versus jumping versus running) occurring at the among-individual level. We further modelled individual (co)variation in age-related plasticity of performance and found previously unseen trade-offs in throwing versus running performance that manifest through ageing. Our results verify that human performance is limited by fundamental genetic, environmental and ageing constraints that preclude the simultaneous improvement of performance in multiple dimensions. Identifying these constraints is fundamental to understanding performance trade-offs and predicting the ageing of motor function.

Measuring Selection on Physiology in the Wild and Manipulating Phenotypes (in Terrestrial Nonhuman Vertebrates)

To understand why organisms function the way that they do, we must understand how evolution shapes physiology. This requires knowledge of how selection acts on physiological traits in nature. Selection studies in the wild allow us to determine how variation in physiology causes variation in fitness, revealing how evolution molds physiology over evolutionary time. Manipulating phenotypes experimentally in a selection study shifts the distribution of trait variation in a population to better explore potential constraints and the adaptive value of physiological traits. There is a large database of selection studies in the wild on a variety of traits, but very few of those are physiological traits. Nevertheless, data available so far suggest that physiological traits, including metabolic rate, thermal physiology, whole-organism performance, and hormone levels, are commonly subjected to directional selection in nature, with stabilizing and disruptive selection less common than predicted if physiological traits are optimized to an environment. Selection studies on manipulated phenotypes, including circulating testosterone and glucocorticoid levels, reinforce this notion, but reveal that trade-offs between survival and reproduction or correlational selection can constrain the evolution of physiology. More studies of selection on physiological traits in nature that quantify multiple traits are necessary to better determine the manner in which physiological traits evolve and whether different types of traits (dynamic performance vs. regulatory) evolve differently.

Differential contributions of ApoE4 and female sex to BACE1 activity and expression mediate Aβ deposition and learning and memory in mouse models of Alzheimer's disease

Alzheimer’s disease (AD), the most common form of dementia, disproportionately affects women in both prevalence and severity. This increased vulnerability to AD in women is strongly associated with age-related ovarian hormone loss and apolipoprotein E 4 allele (ApoE4), the most important genetic risk factor for sporadic AD. Up to date, the mechanism involved in the interaction between ApoE4 and sex/gender in AD is still unclear. This study evaluated the sex-dependent ApoE4 effects on learning and memory, Aβ deposition and potential mechanisms, using mice bearing both sporadic (ApoE4) and familial (APP_Swe, PS1_M146V, tau_P301L; 3xTg) AD risk factors and compared with sex- and age-matched 3xTg or nonTg mice. Compared to nonTg mice, transgenic mice of both sexes showed spatial learning and memory deficits in the radial arm water maze and novel arm discrimination tests at 20 months of age. However, at 10 months, only ApoE4/3xTg mice showed significant learning and memory impairment. Moreover, molecular studies of hippocampal tissue revealed significantly higher protein levels of Aβ species, β-site APP cleavage enzyme (BACE1) and Sp1, a transcription factor of BACE1, in female ApoE4/3xTg when compared with female nonTg, female 3xTg, and male ApoE4/3xTg mice. Significantly increased BACE1 enzymatic activities were observed in both male and female mice carrying ApoE4; however, only the females showed significant higher BACE1 expressions. Together, these data suggest that ApoE4 allele is associated with increased BACE1 enzymatic activity, while female sex plays an important role in increasing BACE1 expression. The combination of both provides a molecular basis for high Aβ pathology and the resultant hippocampus-dependent learning and memory deficits in female ApoE4 carriers.

Relationships among traits of aerobic and anaerobic swimming performance in individual European sea bass Dicentrarchus labrax

Teleost fishes exhibit wide and temporally stable inter-individual variation in a suite of aerobic and anaerobic locomotor traits. One mechanism that could allow such variation to persist within populations is the presence of tradeoffs between aerobic and anaerobic performance, such that individuals with a high capacity for one type of performance have a reduced capacity for the other. We investigated this possibility in European seabass Dicentrarchuslabrax, each measured for a battery of indicators of maximum locomotor performance. Aerobic traits comprised active metabolic rate, aerobic scope for activity, maximum aerobic swimming speed, and stride length, using a constant acceleration test. Anaerobic traits comprised maximum speed during an escape response, maximum sprint speed, and maximum anaerobic burst speed during constant acceleration. The data provided evidence of significant variation in performance among individuals, but there was no evidence of any trade-offs among any traits of aerobic versus anaerobic swimming performance. Furthermore, the anaerobic traits were not correlated significantly among each other, despite relying on the same muscular structures. Thus, the variation observed may reflect trade-offs with other morphological, physiological or behavioural traits.

The effects of temperature and inter-individual variation on the locomotor performance of juvenile turtles

The effects of temperature on aquatic and terrestrial locomotor performance, including measures of burst speed, endurance, and righting response, the inter-individual correlation between measures of locomotor performance, and the temporal repeatability of performance were assessed in juvenile western painted turtles, Chrysemys picta bellii. Locomotor performance increased as temperature increased, with Q(10) values ranging from 1.33 to 1.98 for burst speed and 2.28 to 2.76 for endurance measures. Righting response performance also increased with temperature. Aquatic and terrestrial measures of locomotor performance were highly correlated; however, righting response was not correlated with any other measure of performance. Measures of terrestrial locomotor performance were highly repeatable over the entire 30-week study period, whereas aquatic locomotor performance was only repeatable through week 12. The righting response was repeatable over a 6-week study period. Both the interindividual variation and temperature effects on locomotor performance likely influences the survival of turtles, especially juveniles, by affecting the length of time turtles are exposed to potential predators and their ability to escape.

Inter- and intrastrain variation in mouse critical running speed

With the generation of mouse models of human cardiovascular or neuromuscular disorders, the development of noninvasive methods to evaluate the physiological responses to exercise presents an important challenge. The possibility for determining critical speed (CS) in the mouse model was examined according to strain (CD1, C57BL/6J, FVB/N) and sex. Sixty mice performed four exhaustive runs on a treadmill to determine their CS. Twenty-one performed an incremental test to determine the velocity at the lactate threshold. CS was significantly different between the strains ( P < 0.0001) but not between sexes. Two measures of heritability showed that CS was partially heritable. CS was not significantly different from lactate threshold velocity. We conclude that CS, which reflects the aerobic capacity, can be determined in mice, as in humans and horses. Considering the intrastrain variability, CS could represent a valuable means for designing an optimal and individualized physical training in mice.

Genetic influence on daily wheel running activity level

This project was designed to determine the genetic (between-strain) and environmental (within-strain) variance in daily running wheel activity level in inbred mice. Five male and five female mice, 9.7–15.3 wk old, from each of 13 strains (A/J, AKR/J, BALB/cJ, C3H/HeJ, C57Bl/6J, C57L/J, C3Heb/FeJ, CBA/J, DBA/2J, SWR/J, MRL/MpJ, SPRET/Ei, and CAST/Ei) as well as five female NZB/BinJ mice were housed individually. A running wheel in each cage was interfaced with a magnetic sensor to measure total daily distance and exercise time for each animal every 24 h for 21 consecutive days (3 wk). Average daily distance (km), duration (min), and velocity (m/min) for each strain was then calculated. Significant interstrain differences in average daily distance ( P < 0.001), average daily exercise duration ( P < 0.0001), and average daily exercise velocity ( P < 0.0001) were found, with C57L/J mice running farther and faster than the other strains. Sex was a significant factor in daily running wheel activity, with female mice running an average of 20% farther ( P = 0.01) and 38% faster ( P < 0.0001) than male mice. The male mice ran 15% longer duration on a daily basis ( P = 0.0091). Weight was only associated with exercise velocity in the female mice, but this relationship was not significant when subdivided by strain. Broad-sense heritability estimates on the physical activity differed by sex (for distance, male 31–48% and female 12–22%; for duration, male 44–61% and female 12–21%; for velocity, male 49–66% and female 44–61%). In conclusion, these data indicate that daily running wheel activity level in mice is significantly affected by genetic background and sex.

Artificial selection for intrinsic aerobic endurance running capacity in rats

Artificial selection for intrinsic aerobic endurance running capacity was started using genetically heterogeneous N:NIH stock of rats as a founder population (n = 168). Selection for low and high capacity was based upon distance run to exhaustion on a motorized treadmill using a velocity-ramped running protocol. The starting velocity was 10 m/min and was increased by 1 m/min every 2 min (slope was constant at 15 degrees ). At each generation, within-family selection was practiced using 13 families for both the low and high lines. A rotational breeding paradigm maintained the coefficient of inbreeding at less than 1% per generation. On average the founder population ran to exhaustion in 355 +/- 11 m. Six generations of selection produced lines that differed in running capacity by 171%, with most of the change occurring in the high line. At generation 6 the low line ran 310 +/- 8 m and the high line 839 +/- 21 m at exhaustion. Selection for running capacity produced changes in body weight as a correlated trait. By generation 6, the low-line females were 20% heavier than the high-line females, and the low-line males were 16% heavier than the high-line males.