INTERACTIVE EFFECTS OF OFFSPRING SIZE AND TIMING OF REPRODUCTION ON OFFSPRING REPRODUCTION - EXPERIMENTAL, MATERNAL, AND QUANTITATIVE GENETIC-ASPECTS

We demonstrate that egg size in side-blotched lizards is heritable (pa rent-offspring regressions) and thus will respond to natural selection . Because our estimate of heritability is derived from free-ranging li zards, it is useful for predicting evolutionary response to selection in wild populations. Moreover, our estimate for the heritability of eg g size is not likely to be confounded by nongenetic maternal effects t hat might arise from egg size per se because we estimate a significant parent-offspring correlation for egg size in the face of dramatic exp erimental manipulation of yolk volume of the egg. Furthermore, we also demonstrate a significant correlation between egg size of the female parent and clutch size of her offspring. Because this correlation is n ot related to experimentally induce maternal effects, we suggest that it is indicative of a genetic correlation between egg size and clutch size. We synthesize our results from genetic analyses of the trade-off between egg size and clutch size with previously published experiment s that document the mechanistic basis of this trade-off. Experimental manipulation of yolk volume has no effect on offspring reproductive tr aits such as egg size, clutch size, size at maturity, or oviposition d ate. However, egg size was related to offspring survival during adult phases of the life history. we partitioned survival of offspring durin g the adult phase of the life history into (1) survival of offspring f rom winter emergence to the production of the first clutch (i.e., the vitellogenic phase of the first clutch), and (2) survival of the offsp ring from the production of the first clutch to the end of the reprodu ctive season. Offspring from the first clutch of the reproductive seas on in the previous year had higher survival during vitellogenesis of t heir first clutch if these offspring came from small eggs. We did not observe selection during these prelaying phases of adulthood for offsp ring from later clutches. However, we did find that later clutch offsp ring from large eggs had the highest survival over the first season of reproduction. The differences in selection on adult survival arising from maternal effects would reinforce previously documented selection that favors the production of small offspring early in the season and large offspring later in the season-a seasonal shift in maternal provi sioning. We also report on a significant parent-offspring correlation in lay date and thus significant heritable variation in lay date. We c an rule out the possibility of yolk volume as a confounding maternal e ffect-between genetic effects (i.e., heritable) and nongenetic materna l effects acting on lay date that arise from the maternal trait lay da te per se (or other unidentified maternal traits). Nevertheless, we de monstrate how the timing of female reproduction (e.g., date of oviposi tion and date of hatching) affect reproductive attributes of offspring . Notably, we find that date of hatching has effects on body size at m aturity and fecundity of offspring from later clutches. We did not det ect comparable effects of lay date on offspring from the first clutch.