Repeatability and phenotypic plasticity of fish swimming performance across a gradient of urbanization

Abstract

How phenotypic plasticity of locomotor performance varies among populations in nature is poorly known. Swimming ability of blacknose dace (Rhinichthys atratulus) from eight different watersheds had previously been shown to depend upon watershed impervious surface cover (ISC) and stream base-flow. Keeping these populations of stream fish under low flow conditions produced changes in locomotor capacity suggestive of phenotypic plasticity varying among the populations. The present experiments were conducted to better understand the plasticity of swimming performance in dace and how urbanization affects dace biology. Two experimental approaches were used: 1) laboratory training of dace populations at two levels of flow for 6 weeks; and, 2) exploring in situ training by capturing fish from relatively fast and slow reaches of three different streams and comparing their swimming abilities at three different scales. Individual sprint and endurance (modified Ucrit) swimming were significantly repeatable across a laboratory training regimen; sprint performance had previously been shown to not be repeatable when dace were held in static water. Both of our approaches suggested that sprint and endurance swimming ability significantly respond to changes in environmental flow. Although there was no evidence for a different magnitude of phenotypic plasticity among populations, urban populations that experience more stochastic flow regimes had more consistent plasticity. Phenotypic plasticity of locomotor performance in response to variable flow appears to be an important characteristic of blacknose dace biology, yet we did not uncover sufficient evidence to suggest that it is under selection in fish adjusting to urban stream habitats.