Maternal effects on egg investment and offspring performance inblack widow spiders

Maternal effects are powerful forces of adaptive evolution but their widespread implications, especially in human-disturbed environments, are still being realized. Here we examine the role of maternal effects in shaping fitness-related behaviour and life-history traits in black widow spiders, Latrodectus hesperus. We test the prediction that adult foraging success shapes maternal body condition, fecundity and egg investment, and that maternal prey abundance has a positive, cross-generational effect on a number of important offspring traits. Our results suggest that maternal foraging success is indeed translated into positive effects on maternal body condition, eggsac mass, egg number, egg mass, egg size, egg density and development rate. Maternal feeding had no effect on sibling cannibalism. Interestingly, despite the statistically significant effects of maternal food regime on offspring parameters listed above, some mothers in the high-food treatment nevertheless made low-density eggs and some mothers in the low-food treatment made high-density eggs. Thus, maternal egg investment, and several other life-history variables, were influenced by a family effect that cannot be explained solely by our manipulation of maternal foraging. For example, a strong effect of family on the latency to sibling cannibalism, in the absence of any link between maternal food regime, egg density and cannibalism, suggests that direct genetic effects, rather than maternal effects, may explain this fitness-related behavioural trait. We discuss the implications of these findings for our understanding of the behaviour, ecology and evolution of this and other arthropods, with particular reference to the possibility that maternal effects may facilitate rapid evolution to human-disturbed habitats.