Meeting Abstract

5.5  Sunday, Jan. 4  Evolution of maternal effects in sister salamander species LANDBERG, Tobias; University of Connecticut tobias.landberg@uconn.edu

Egg size is a key life history trait of amphibians that varies dramatically across almost every level of organization from within individuals to between habitats. Despite harboring great adaptive potential, the phenotypic effects of egg size variation have remained elusive because other sources of variation are difficult to control or measure. To begin to address this question, I experimentally removed small quantities of yolk from embryonic salamanders of two closely related species (Ambystoma texanum & A. barbouri) that live in ponds and streams respectively. While the adults are essentially indistinguishable, they differ in reproductive traits including egg size, egg number and larval traits such as stage at hatching and time to metamorphosis. This allometric engineering experiment utilized a split-clutch design, several levels of yolk removal and a sham that controlled for the surgical procedure without actual yolk removal. Animals that had the most yolk removed hatched earliest indicating that some of the species differences in hatching time are explained by differences in yolk reserves. Body size was not as strongly affected in the pond species as it was in the stream species. Survival rates also showed interactions between species and treatment. Surprisingly, developmental rates did not appear to be strongly affected, however analysis is ongoing. Egg size effects have potential to cascade through ontogeny affecting multiple fitness-related traits and can therefore be viewed as a means of integrating complex phenotypes and potentially addressing multiple selective problems simultaneously. However, any one selective agent could drive the evolution of many traits if egg size responds to selection. This study has revealed that the plastic response to egg size can evolve even among closely related species.