Meeting Abstract
Salinity tolerance is thought to play an important role in defining range limits for many aquatic species. Yet, the degree to which distribution patterns are determined by local adaptation versus acclimation remains unknown for most aquatic organisms. In Trinidad, the euryhaline guppy (Poecilia reticulata), behaviorally avoids brackish and saltwater. We thus hypothesized that guppies experience some decline in fitness upon entering brackish water. In fact, previous lab work suggests acute exposure to brackish water causes a reduction in activity levels, reaction times, and metabolism. To investigate if long-term acclimation could overcome these challenges, we conducted a common garden experiment. We reared out wild-caught guppies to the second generation (F2) and looked at the effects of developmental plasticity due to salinity rearing conditions on fitness. We split F2 broods at birth and raised them in either fresh (0ppt) or brackish (30ppt) water. Sustained swimming performance was measured in adults under various treatments: their rearing condition and several away environments, mimicking swimming up or down a salinity gradient. Performance was recorded in terms of critical swimming velocity (UCRIT), the maximum swimming velocity a fish can withstand for a given period of time. If populations are locally adapted to freshwater, we predict that guppies reared and tested in freshwater will do better than their counterparts, reared and tested in brackish water. If developmental plasticity can overcome salinity challenges, we predict no difference in performance between fish reared and tested in brackish water and those reared and tested in freshwater.
