Meeting Abstract
Salinity tolerance is a defining factor in shaping geographic range limits of many species. Nonetheless, the influence of salinity tolerance on patterns of dispersal and local adaptation are understudied for most species. Aquatic euryhaline species are capable of acclimating to a wide range of salinities; however, most species typically exhibit a preference. For example, previous work in euryhaline teleosts indicates that crossing a salinity gradient typically results in increased oxygen uptake and energetic costs for the organism. In Trinidad, swamp guppies, Poecilia picta, are found in adjacent fresh and brackish water habitats, but the degree to which these populations are locally adapted to various salinities is unknown. We investigated their physiological responses to changes in salinity on different temporal scales to determine whether the physiological response to variations in salinity is locally adaptive. We split wild-caught individuals from each population and laboratory acclimated them to fresh (0ppt) and brackish (30ppt) water over a 5-month period. Through gradual acclimation, we simulated slow movement along a salinity gradient. We then tested the effect of a rapid acclimation on different individuals through a fast-changing salinity titration to simulate conditions these fish might encounter during dispersal or flooding events. We also quantified the internal osmolality of these fish to determine their ability to maintain osmotic constancy. If the populations are locally adapted, we predict that elevations in metabolic rate will be higher when fish are exposed to their “away” salinity conditions in both treatments. We also predict that plasma osmolality will be closer to the solute concentrations found in the environment of those individuals with the lowest metabolic rate.
