Meeting Abstract
Within heterogeneous environments, mobile species are expected to occupy habitats that maximize fitness. However, competitors and predators might preclude individuals from persisting in these habitats, leading to situations in which a species exists at high abundance in suboptimal environments. Mangrove rivulus fish, Kryptolebias marmoratus, inhabit mangrove ecosystems where salinities range from 0 – 65 ppt but are most often collected at 25 ppt. We examined rivulus’ salinity preference under controlled conditions and in the absence of predators and competitors. We exposed fish to a salinity gradient with chambers containing salinities of 5, 15, 25, 35 and 45 ppt for 8 hours. We defined preference as the salinity in which the fish spent the majority of their time during the trial. To determine whether preferences were repeatable, each fish experienced three trials. Rivulus spent a greater proportion of time in lower salinities (5, 15 ppt), which indicates that, when given the opportunity, rivulus select habitats of lower salinity than they occupy in the wild. We also determined the salinity at which rivulus would lay their eggs by exposing fish to a salinity gradient for 2 weeks. Rivulus showed a significantly greater probability of laying eggs in low salinities compared to control (25 ppt) or high salinities. Evidence from this study suggests that although rivulus can tolerate a wide range of salinities, they prefer salinities approaching freshwater. These results raise questions about factors that prevent rivulus from occupying lower salinities in the wild, whether higher salinities impose energetic costs, and whether fitness changes as a function of salinity.
