Meeting Abstract
Competing selective pressures and trade-offs result in organisms evolving phenotypes that optimize overall performance, leading to local adaptation to particular environments. Selection for any one trait can result in either functional trade-offs or functional facilitation, in which multiple aspects of performance are indirectly influenced. Hence, understanding the functional repercussions of trait variation is critical to understand adaptive evolution of complex phenotypes. Poecilia mexicana (Poecillidae) is a live-bearing fish that inhabits toxic, hydrogen sulfide rich springs and normal freshwater streams. Fish from these two environments are exposed to divergent selection, which has resulted in phenotypic trait divergence and ecological speciation. While trait variation within and among populations has been well described, the functional implications are less clear. Using high-speed videography, we quantified different performance metrics related to variation in morphology in individual fish from sulfidic and nonsulfidic environments: burst speed swimming, steady swimming, and gill ventilation capacity. Fish from nonsulfidic habitats exhibited faster escape responses, while fish from sulfidic environments exhibited higher critical swimming speeds, exerted less effort to maintain any given swimming speed, and had higher gill ventilation capacity. We found evidence for functional trade-offs (between different modes of swimming) and facilitation (between steady swimming and gill ventilation). Overall, performance differences matched predictions based on environmental conditions in each habitat type, with hypoxia and energy-limitation in sulfidic and higher levels of predation in non-sulfidic habitats.
