S1-2.2 Jan. 4 Morphology to Performance to Fitness: Biomechanics and Ecology Predict Evolutionary Divergence in a Livebearing Fish LANGERHANS, R.B.; Harvard University firstname.lastname@example.org
To examine whether evolutionary outcomes can be predicted from first principles, I test predictions of phenotypic evolution based on biomechanical and ecological knowledge regarding the relationships between body morphology, swimming performance, and fitness in a livebearing fish. Resource competition is expected to generate selection favoring enhanced prolonged swimming performance in low-predation environments (important for foraging, acquiring mates, reserving energy for reproduction), whereas predation is expected to create selection favoring enhanced fast-start swimming performance in high-predation environments (important for evading predator strikes). Gambusia (mosquitofishes) use body-caudal fin steady and unsteady propulsion for prolonged and fast-start swimming respectively. Because this locomotor system is mechanically coupled, optimizing one swimming mode necessarily compromises the other (i.e. performance tradeoff). Specifically, prolonged swimming is optimized with a relatively shallow caudal peduncle and a deep anterior body/head region (fusiform body shape), while fast-start swimming is optimized with the opposite trait values (deep caudal peduncle, shallow anterior body/head). This scenario creates specific predictions regarding phenotypic divergence between predator regimes. I test these biomechanical (morphology = performance) and ecological (performance = fitness) assumptions, as well as their resulting predictions for divergent evolutionary trajectories in different predatory environments for a post-Pleistocene radiation of Bahamas mosquitofish (G. hubbsi) inhabiting blue holes (vertical solution caves). All predictions are upheld, resulting in strong morphological divergence between predator regimes matching a priori predictions.