Abstract

Life-history theory is a central component of evolutionary biology, which predicts that organisms trade-off investing their finite energy into growth or reproduction to maximize their fitness. Yet, experimental studies seldomly assess the extent to which maternal life-histories vary across populations, life-stages or their interactions. Brook trout (Salvelinus fontinalis) are an excellent model system to examine such variation, as diverse populations can be isolated despite occurring within small scales (25km2) in nature. Using two common garden experiments over three years, we assessed the influence of environmental and population variation on maternal and early life history responses. First, we captive-reared four wild brook trout populations under four feed treatments to assess five maternal life history responses for 403 females. As early juveniles, we reared fish on a low-variability, high-food or a high variability, low-food treatment. As late juveniles until maturation, we switched half the individuals to the opposite food treatment, while the other half remained unchanged. In a second experiment, we reared offspring produced by the crosses from the previous experiment under a thermal stress gradient to investigate transgenerational plasticity of early life history traits. We found that females grew faster in resource-rich environments, consistent with the life history theory that they would mature at larger body sizes, producing many, small eggs compared to females in resource-poor environments. Moreover, energy allocation into reproductive trade-offs varied substantially by population and life-stage, suggesting populations are locally adapted to their environments. Remarkably, manipulations to the maternal environment elicited limited transgenerational plasticity in offspring exposed to thermal variability and stress. Our study highlights the extent to which maternal phenotypic plasticity is moderated by population effects across life-stages and environmental gradients.