MATERNAL EFFECTS MEDIATE HOST EXPANSION IN ASEED-FEEDING BEETLE

Abstract

Texas ebony (Chloroleucon ebano) has recently been introduced as an ornamental tree in the Phoenix metropolitan area of Arizona (USA). It has since been colonized by the seed beetle Stator limbatus (Coleoptera: Bruchidae), and seeds of Texas ebony support the development of beetles to reproductive maturity in nature and in the laboratory. Egg size affects the larval survivorship of beetles on seeds of Texas ebony. Females of S. limbatus exhibit egg-size plasticity in response to native host plants; they lay small eggs if they encounter seeds of catclaw acacia (Acacia greggii) and lay large eggs if they encounter seeds of the blue paloverde (Cercidium floridum). We tested the hypothesis that oviposition experiences of female S. limbatus on native plants affects the ability of their larvae to develop on seeds of the nonnative Texas ebony. We demonstrate that females that encounter the native C. floridum while they are maturing their eggs produce progeny that have survivorship 10 times higher on seeds of the introduced Texas ebony than that of progeny produced by females that do not encounter C. floridum during egg maturation. However, this result cannot be explained entirely by egg-size plasticity; survivorship of larvae differed among treatments even in the range of egg sizes that overlapped between treatments. These results thus indicate that females exhibit plasticity in egg size and egg composition, and that this plasticity facilitates the expansion of S. limbatus onto seeds of a nonnative plant. Our study thus demonstrates that maternal effects can influence species interactions within communities, and that we should consider these maternal effects when predicting the ecological and evolutionary consequences of changing species distributions.