title: Trade-off between steady and unsteady swimming underlies predator-driven divergence in Gambusia affinis.
abstract: Differences in predation intensity experienced by organisms can lead to divergent natural selection, driving evolutionary change. Western mosquitofish (Gambusia affinis) exhibit larger caudal regions and higher burst-swimming capabilities when coexisting with higher densities of predatory fish. It is hypothesized that a trade-off between steady (constant-speed cruising; important for acquiring resources) and unsteady (rapid bursts and turns; important for escaping predators) locomotion, combined with divergent selection on locomotor performance (favouring steady swimming in high-competition scenarios of low-predation environments, but unsteady swimming in high-predation localities) has caused such phenotypic divergence. Here, I found that morphological differences had a strong genetic basis, and low-predation fish required less hydromechanical power during steady swimming, leading to increased endurance. I further found individual-level support for cause-and-effect relationships between morphology, swimming kinematics and endurance. Results indicate that mosquitofish populations inhabiting low-predation environments have evolved increased steady-swimming abilities via stiffer bodies, larger anterior body/head regions, smaller caudal regions and greater three-dimensional streamlining.
authors.affiliation: Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA. langerhans@ou.edu
authors.forename: R B
authors.initials: RB
authors.lastname: Langerhans
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D001696:Biomechanical Phenomena; D001837:Body Weights and Measures; D003532:Cyprinodontiformes / Q000502:physiology*; D015999:Multivariate Analysis; D010807:Physical Endurance / Q000502:physiology*; D011235:Predatory Behavior / Q000502:physiology; D012641:Selection, Genetic; D013550:Swimming / Q000502:physiology*; D013623:Tail / Q000033:anatomy & histology