Meeting Abstract
Associations among traits can influence the rates of organismal responses to climate change, which is altering multiple abiotic variables in aquatic habitats, including temperature and oxygenation. As both high temperatures and hypoxia limit the capacity to maintain aerobic metabolic balance, it has been hypothesized that a mechanistic association between upper thermal tolerance limits and hypoxia tolerance limits may be a common feature of aquatic vertebrates. We have tested the predictions of this hypothesis using Atlantic killifish, Fundulus heteroclitus. Populations of this species are distributed along the east coast of North America, and northern and southern populations are genetically and physiologically distinct. Southern fish have greater tolerances of high temperatures and hypoxia than northern fish, consistent with a positive association between these traits. However, this pattern could also be due to independent divergence of each trait between the subspecies. To distinguish these alternatives, we measured the thermal and hypoxia tolerances of killifish from eight populations along the coast, including populations located in two contact zones between the subspecies. Thermal tolerance varied linearly with latitude, whereas hypoxia tolerance transitioned sharply from northern to southern values across both contact zones. In addition, no trait correlations were observed within contact zone populations. These results indicate that thermal and hypoxia tolerance limits are unlikely to share underlying mechanistic bases in this species, and that, contrary to prediction, an association between these limits is not a common feature of all aquatic species.
