Meeting Abstract
Natural selection drives the evolution of traits to optimize organismal performance in the context of their environment. However, optimization of one trait or function may adversely impact the expression of other traits and functions, and complex phenotypes inadvertently represent a comprise of balancing different needs. Functional trade-offs can consequently impact evolutionary outcomes and influence phenotypic variation along environmental gradients. We tested how morphological variation of fish along a natural toxicity gradient impacts organismal function in terms of locomotion and ventilation. Several lineages of Poecilia mexicana (Poeciliidae) have colonized toxic, hydrogen sulfide rich springs. Adjacent populations in sulfide springs and regular stream habitats face strong and multifarious divergent selection from abiotic and biotic environmental conditions. For example, fish in sulfide springs are exposed to high toxicity and hypoxia, high levels of intra-specific competition and relatively few aquatic predators. In contrast, fish inhabiting normal freshwater streams are exposed to higher levels of oxygen and more complex communities (higher levels of inter-specific competition and predation). We quantified variation in morphology and used high-speed videography to quantify different performance metrics in individual fish from sulfidic and non-sulfidic populations, including aspects of burst speed, steady swimming, and gill ventilation capacity. Data are used to test for correlations between specific morphological traits and aspects of swimming and ventilation performance as well as for trade-offs between different modes of swimming and oxygen acquisition.
