Interspecific Differences in Metabolic Rate and Metabolic Temperature Sensitivity Create Distinct Thermal Ecological Niches in Lizards (Plestiodon)

Three congeneric lizards from the southeastern United States (Plestiodon fasciatus, P. inexpectatus, and P. laticeps) exhibit a unique nested distribution. All three skink species inhabit the US Southeast, but two extend northward to central Ohio (P. fasciatus and P. laticeps) and P. fasciatus extends well into Canada. Distinct interspecific differences in microhabitat selection and behavior are associated with the cooler temperatures of the more Northern ranges. We hypothesized that interspecific differences in metabolic temperature sensitivity locally segregates them across their total range. Resting oxygen consumption was measured at 20 degrees, 25 degrees and 30 degrees C. Plestiodon fasciatus, from the coolest habitats, exhibited greatly elevated oxygen consumption compared to the other species at high ecologically-relevant temperatures (0.10, 0.17 and 0.83 ml O-2.g(-1).h(-1) at 20 degrees, 25 degrees and 30 degrees C, respectively). Yet, P. inexpectatus, from the warmest habitats, exhibited sharply decreased oxygen consumption compared to the other species at lower ecologically-relevant temperatures (0.09, 0.27 and 0.42 ml O-2.g(-1).h(-1) at 20 degrees, 25 degrees and 30 degrees C, respectively). Plestiodon laticeps, from both open and closed microhabitats and intermediate latitudinal range, exhibited oxygen consumptions significantly lower than the other two species (0.057, 0.104 and 0.172 ml O-2.g(-1).h(-1) at 20, 25 degrees and 30 degrees C, respectively). Overall, Plestiodon showed metabolic temperature sensitivities (Q(10)s) in the range of 2-3 over the middle of each species' normal temperature range. However, especially P. fasciatus and P. inexpectatus showed highly elevated Q(10)s (9 to 25) at the extreme ends of their temperature range. While morphologically similar, these skinks are metabolically distinct across the genus' habitat, likely having contributed to their current distribution.