Fast adjustment of pace-of-life and risk-taking to changes in food quality by altered gene expression in house mice

The pace-of-life syndrome hypothesis provides a framework for the adaptive integration of behaviour, physiology and life history between and within species. It suggests that behaviours involving a risk of death or injury should co-vary with a higher allocation to fast reproduction. Empirical support for this hypothesis is mixed, presumably because important influencing factors such as environmental variation, are usually neglected. By experimentally manipulating food quality of wild mice living under semi-natural conditions for three generations, we show that individuals adjust their life history strategies and risk-taking behaviours as well as trait covariation (N_individuals  = 1442). These phenotypic differences are correlated to differences in transcriptomic gene expression of primary metabolic processes in the liver while no changes in gene frequencies occurred. Our discussion emphasises the need to integrate the role of environmental conditions and phenotypic plasticity in shaping relationships among behaviour, physiology and life history in response to changing environmental conditions.

Fitness, risk taking, and spatial behavior covary with boldness in experimental vole populations

Individuals of a population may vary along a pace-of-life syndrome from highly fecund, short-lived, bold, dispersive "fast" types at one end of the spectrum to less fecund, long-lived, shy, plastic "slow" types at the other end. Risk-taking behavior might mediate the underlying life history trade-off, but empirical evidence supporting this hypothesis is still ambiguous. Using experimentally created populations of common voles (Microtus arvalis)-a species with distinct seasonal life history trajectories-we aimed to test whether individual differences in boldness behavior covary with risk taking, space use, and fitness. We quantified risk taking, space use (via automated tracking), survival, and reproductive success (via genetic parentage analysis) in 8 to 14 experimental, mixed-sex populations of 113 common voles of known boldness type in large grassland enclosures over a significant part of their adult life span and two reproductive events. Populations were assorted to contain extreme boldness types (bold or shy) of both sexes. Bolder individuals took more risks than shyer ones, which did not affect survival. Bolder males but not females produced more offspring than shy conspecifics. Daily home range and core area sizes, based on 95% and 50% Kernel density estimates (20 ± 10 per individual, n = 54 individuals), were highly repeatable over time. Individual space use unfolded differently for sex-boldness type combinations over the course of the experiment. While day ranges decreased for shy females, they increased for bold females and all males. Space use trajectories may, hence, indicate differences in coping styles when confronted with a novel social and physical environment. Thus, interindividual differences in boldness predict risk taking under near-natural conditions and have consequences for fitness in males, which have a higher reproductive potential than females. Given extreme inter- and intra-annual fluctuations in population density in the study species and its short life span, density-dependent fluctuating selection operating differently on the sexes might maintain (co)variation in boldness, risk taking, and pace-of-life.