Meeting Abstract

53.5  Tuesday, Jan. 5  Oxygen-induced plasticity and evolution of larval tail morphology in stream and pond-breeding salamanders (genus Ambystoma) LANDBERG, Tobias; University of Connecticut tobias.landberg@uconn.edu

Adaptive variation in larval ecotypes has evolved in five salamander families, but the environmental contributions to evolutionary differences are barely explored. Large gills and tail fins contribute to gas exchange in low-oxygen pond-dwelling larvae. Reduced gills and tail area in stream dwelling larvae decrease drag and should mitigate against drifting in high flow (and high oxygen) streams. I investigated the evolution of larval morphology in two salamander species with ancestral pond-dwelling larval habits (Ambystoma maculatum & A. texanum) and one derived stream species (A. barbouri). As predicted, the derived stream species has a shorter tail relative to snout vent length and smaller tail area relative to tail length than its pond-breeding sister species, A. texanum. In all three species, tail fin area decreased in high oxygen relative to low oxygen. Oxygen-induced tail area plasticity contributes to evolutionary differences between stream and pond species because wild oxygen levels differ. When raised similarly, the difference between pond and stream sister species decreased. However, fixed differences in egg size–snout/vent length and relative tail length account for the majority of sister species’ differences. Since the ancestral response to oxygen was apparently in the direction of tail shape evolution in the derived stream larvae, primitively pond-breeding salamanders similar to A. texanum invading streams 1-2 million years ago would have experienced relatively high oxygen levels and an induced plastic response that reduced tail area. This underscores that environmentally-induced variation not only contributes to current adaptive phenotypes, but can serve as a primary source of initial variation for adaptation.