Fox 9807315 In many organisms, a female's environment provides a reliable indicator of the environmental conditions that her progeny will encounter. In such cases, maternal effects may evolve as mechanisms for trans-generational phenotypic plasticity, whereby, in response to a predictive environmental cue (such high or low host density, short or long photoperiod), a mother can change the type of eggs that she makes, or can program a developmental switch in her offspring, producing offspring prepared for the environmental conditions predicted by the cue. These maternal effects often have a genetic basis, and appear to be adaptive in many organisms. Yet little is understood about the evolutionary genetics of maternal effects or the nature and consequences of selection on maternal effects, such that the potential for them to respond to natural selection remains largely speculative. This proposal describes a series of experiments designed to test hypotheses that explain the evolution of egg size, egg number, and egg size plasticity (an apparently adaptive maternal effect) in a seed beetle, Stator limbatus. Specifically, this research will (1) quantify the sources of this phenotypic variation (genetic, maternal, paternal, and environmental) in egg size and egg size plasticity within populations of S. limbatus; (2) test the hypothesis that selection for improved survivorship when larvae develop on seeds of Cercidium floridum (blue paloverde) results in the evolution of larger egg size; (3) test the hypothesis that selection for increased fecundity results in the evolution of smaller egg size; (4) test the hypothesis that the evolution of egg size plasticity is constrained by the genetic correlation between the size of eggs laid in response to Acacia greggii (catclaw acacia) and the size of eggs laid on C. floridum; (5) test the hypothesis that the genetic correlation across hosts evolves in response to selection on egg size and egg size plasticity. Maternal effe cts are ubiquitous in nature; they are important in generating many of the phenotypic patterns and population dynamics that we observe, and are often important components of population responses to natural selection. In fact, evolutionary responses to selection may be manifest through maternal effects, such that maternal effects may provide mechanisms for adapting to variable environments. However, the evolutionary dynamics of maternal effects, and characters influenced by maternal effects, have been little explored. In lab and field experiments, selection can be demonstrated to favor or oppose the evolution of maternal effects. However, demonstrating selection favoring the evolution of a maternal effect is not sufficient evidence to demonstrate that a maternal effect has evolved as an adaptation. The same rigorous techniques applied to studies of behavior, morphology, and life history need now be applied to the study of maternal effects to determine how pervasive adaptive maternal effects are in nature and how often maternal effects evolve simply as consequences of the evolution of parental and offspring characters. The objectives of these experiments are (a) to study the evolutionary genetics of an adaptive maternal effect (egg size plasticity in the seed beetle, Stator limbatus), using rigorous quantitative genetic experimental designs, and (b) to simulate natural selection on the maternal effect as it is thought to occur in nature to study the evolution of both the maternal effect and correlated life history characters.
