GENETIC CORRELATIONS BETWEEN BASAL AND MAXIMUM METABOLIC RATES IN A WILD RODENT: CONSEQUENCES FOR EVOLUTION OF ENDOTHERMY

The metabolic performance predicts home range size of bank voles: a support for the behavioral-bioenergetics theory

The pace-of-life syndrome describes covariation between life-history, behavioral and physiological traits; while, the emerging behavioral-bioenergetics theory proposes mechanistic links between those traits in a spatial-ecological context. However, little is known about the association between the limits to metabolic rate and spatial performance (i.e., mobility, home range size) in free-living individuals. Here we show, for the first time at the intra-specific level, that mobility traits increased with the aerobic exercise capacity ([Formula: see text]O₂max) in a wild rodent, the bank vole (Myodes glareolus): [Formula: see text]O₂max affected directly the movement intensity, which in turn affected home ranges. The results show that evolution of high [Formula: see text]O₂max could be driven by selection for spatial performance traits, and corroborate one of the key assumptions of the behavioral-bioenergetics theory. However, the minimum maintenance metabolism, measured as the basal metabolic rate (BMR), was not correlated with movement intensity, and the direction of the BMR-home range correlation tended to change with age of the voles. The latter result indicates that testing the theory will be particularly challenging.

Selection for increased mass-independent maximal metabolic rate suppresses innate but not adaptive immune function

Both appropriate metabolic rates and sufficient immune function are essential for survival. Consequently, eco-immunologists have hypothesized that animals may experience trade-offs between metabolic rates and immune function. Previous work has focused on how basal metabolic rate (BMR) may trade-off with immune function, but maximal metabolic rate (MMR), the upper limit to aerobic activity, might also trade-off with immune function. We used mice artificially selected for high mass-independent MMR to test for trade-offs with immune function. We assessed (i) innate immune function by quantifying cytokine production in response to injection with lipopolysaccharide and (ii) adaptive immune function by measuring antibody production in response to injection with keyhole limpet haemocyanin. Selection for high mass-independent MMR suppressed innate immune function, but not adaptive immune function. However, analyses at the individual level also indicate a negative correlation between MMR and adaptive immune function. By contrast BMR did not affect immune function. Evolutionarily, natural selection may favour increasing MMR to enhance aerobic performance and endurance, but the benefits of high MMR may be offset by impaired immune function. This result could be important in understanding the selective factors acting on the evolution of metabolic rates.

Locomotion in response to shifting climate zones: not so fast

Although a species' locomotor capacity is suggestive of its ability to escape global climate change, such a suggestion is not necessarily straightforward. Species vary substantially in locomotor capacity, both ontogenetically and within/among populations, and much of this variation has a genetic basis. Accordingly, locomotor capacity can and does evolve rapidly, as selection experiments demonstrate. Importantly, even though this evolution of locomotor capacity may be rapid enough to escape changing climate, genetic correlations among traits (often due to pleiotropy) are such that successful or rapid dispersers are often limited in colonization or reproductive ability, which may be viewed as a trade-off. The nuanced assessment of this variation and evolution is reviewed for well-studied models: salmon, flying versus flightless insects, rodents undergoing experimental evolution, and metapopulations of butterflies. This work reveals how integration of physiology with population biology and functional genomics can be especially informative.