Phenotypic and Evolutionary Plasticity of Organ Masses in Response to Voluntary Exercise in House Mice

Abstract

We used a novel mouse model to study the effects of selective breeding for high locomotor activity (14 generations) on relative organ sizes, hematocrit (Hct), and blood hemoglobin (Hb) concentration. We also examined effects of exercise training and genotype-by-environment interactions by housing animals for 8 weeks with wheels that were either free to rotate or locked. Mice from the four replicate High-Runner (HR) lines were smaller in total body mass but had larger body mass-adjusted kidneys relative to the four Control lines (P < 0.05). Control and HR lines did not differ significantly for mass-adjusted tail length or masses of the "triceps surae" hindlimb muscle group, heart (ventricle), spleen, liver, adrenal glands or gonads. Wheel access caused a reduction in body mass and an increase in relative heart mass. In females only, wheel access caused a reduction in relative spleen mass. Wheel access did not affect relative tail length or relative mass of the triceps surae, liver, adrenal gland or gonads. Significant interactions between selection history and wheel access were observed in females for spleen, liver, and gonad mass as well as Hct and Hb. Wheel access caused increases in both Hct and Hb, mainly in the HR lines. The mini-muscle phenotype, caused by a Mendelian recessive allele that halves hindlimb muscle mass, was significantly associated with several other body composition traits, including reduced body mass, increased tail length, increased heart mass, increased liver mass (females only), increased mean adrenal gland mass (females only), increased mean kidney mass (males only), and reduced Hct (wheel-access females only). Results are discussed in context of the beneficial acclimation hypothesis, genotype-by-environment interactions, and the potential for "nurture" to be self-reinforcing of "nature" in some complex behavioral-physiological phenotypes.

Erythropoietin elevates but not voluntary wheel running in mice

“…Liver mass was larger in the minimuscle phenotype, as has been reported previously (Garland et al, 2002;Swallow et al, 2005) but did not vary with line type or EPO treatment (Table3). Ventricle mass was greater in HR lines but did not vary statistically with mini-muscle phenotype or EPO treatment.…”

“…The lungs, liver, spleen, triceps surae muscles and ventricles of the heart were removed and weighed (±0.001g) as previously described Swallow et al, 2005;Hannon et al, 2008). Additionally, the lungs were placed in a drying oven at 60°C for seven days, and then weighed to obtain a dry mass.…”

Wheel-running activity and energy metabolism in relation to ambient temperature in mice selected for high wheel-running activity

“…In concurrence with an increase in wheel-running activity, mass-specific DEE was significantly increased in selected mice compared with controls. RMR did not differ between control and selected mice, even though there are differences in body composition between them (Swallow et al 2005). Apparently, the costs for thermoregulation and maintenance of the Using linear regression, slopes and intercepts of the relationship between running speed and metabolic rate (Fig.…”

Latitudinal and longitudinal clines of phenotypic plasticity in the invasive herb Solidago canadensis in China

“…Phenotypic plasticity of widespread species may show clear geographical patterns (Swallow et al 2005;Overgaard et al 2011). According to the climatic variability hypothesis (Janzen 1967;Stevens 1989), individuals of a species should show higher phenotypic plasticity in physiological and morphological traits or a broader range of physiological tolerance when climatic variability increases, as happens for temperature with increasing latitude.…”