Meeting Abstract
Thermal tolerance has been implicated in shaping the range limits of organisms along temperature gradients. Tropical environments, characterized by stable climatic regimes, are thought to favor the evolution of narrow thermal tolerances and greater species turnover across elevation gradients. On the other hand, temperate environments with variable thermal regimes may favor broader tolerance and species distributions. Few studies have examined thermal tolerance patterns in aquatic systems, where fluctuations in temperature are reduced relative to air. An understanding of thermal tolerance may be crucial in revealing which species are vulnerable to climate warming. We focused on phylogenetically related mayflies (Family: Baetidae) collected from low- to high-elevation shallow freshwater streams in the Ecuadorian Andes (tropical, stable climate) and the Colorado Rockies (temperate, variable climate). Thermal tolerance was measured using metabolic rate and critical thermal (CT) limits. Metabolic rate curves were calculated by measuring oxygen consumption across a range of temperatures to determine the thermal breadth for each species. We found that overall, tropical mayflies have narrower thermal breadths than their temperate counterparts. Moreover, thermal optima match the natural thermal variation experienced by mayflies in streams. But while CTmax values indicate that mayflies exhibit high heat tolerance, the metabolic rate experiments demonstrate that insects from both locations have a strong preference for colder temperatures. We therefore suggest that multiple experimental approaches should be used when assessing vulnerability to warming, as a single technique can lead to erroneous conclusions.
