Meeting Abstract
Euryhaline fish species can deal with a wide range of salinities. However, the extent to which populations may deal with different salinity levels through plasticity versus adaptation remains an underexplored question. Previous work in euryhaline teleosts suggests local adaptation to a given range of salinity, and outside this range, fish exhibit elevated stress responses (e.g. increased oxygen uptake and circulating cortisol levels). However, because circulating plasma cortisol levels and metabolic rates are involved in both osmoregulation and stress responses, the use of such physiological measures to distinguish local adaptation from adaptive plasticity is complicated. Here, we compare populations of Trinidadian swamp guppies, Poecilia picta, that are found in adjacent fresh, brackish, and marine habitats, to test if populations are locally adapted to various salinities. We investigated the effects of salinity on field plasma cortisol levels and oxygen consumption in swamp guppies collected from three drainages. In the lab, we tested if these patterns persisted after short- and long-term acclimation to different salinities. In the field, we found circulating cortisol levels were lowest under stable salinity levels (0ppt and 20+ppt) but elevated in sites where salinity fluctuated. Oxygen consumption was highest in the home salinity levels and lowest in “away” salinities over the short-term, and differences among populations were maintained even after long-term acclimation, suggesting populations are locally adapted. Collectively, these results suggest the degree of environmental variability in salinity shapes plastic and evolved physiological responses of populations.
