Despite evidence of maternal age effects in a number of teleost species, there have been challenges to the assertion that maternal age intrinsically influences offspring quality. From an evolutionary perspective, maternal age effects require young females to paradoxically invest in less fit offspring despite a greater fitness benefit from allocating energy to growth. While there exists a narrow range of conditions leading to a maternal fitness benefit via production of lower quality offspring, evolutionary theorists suggest these conditions are seldom met and that the reported maternal age effects are more likely products of the environmental context, so-called context-dependent maternal effects. In the the live-bearing rockfishes of the northeast Pacific (genus Sebastes), maternal age effects were first identified in controlled laboratory settings; therefore, we set out to investigate the apparent paradox of maternal age effects in rockfish by sampling Pacific ocean perch (Sebastes alutus) females over the course of the spawning season in the Gulf of Alaska in three consecutive years. Our goal was to identify the maternal effects operating on offspring provisioning via oil globule volume, and attempt to evaluate any such maternal effects as an intrinsic effect of maternal age or a context-dependent effect of the environment.
We found a maternal age effect on offspring release timing, older females begin spawning earlier in the season than younger females, and on offspring provisioning, older females provisioned their larvae with larger oil globules. In addition, larval provisioning decreased through the spawning season regardless of maternal age, but older females maintained increased provisioning over younger females. A temporal decrease in offspring provisioning could result from females responding to environmental changes, such as the timing of the spring transition, typified by an increase in phytoplankton production. Increased offspring provisioning early in the spawning season when food resources are scarce could be a fitness advantage if the spring transition begins weeks into the pelagic larval duration. These results suggest that both a maternal age effect and a context-dependent environmental effect related to release timing are operating on offspring quality in this species, carrying important implications for including a suite of maternal effects when modeling population persistence and resilience. The evolutionary paradox of the maternal age effect does not uniformly dismiss maternal age effects, but prompts a closer examination of reproductive strategies, which ultimately supports the conservation and fisheries objectives of maintaining healthy populations of marine teleosts in an increasingly uncertain environment.