The influence of habitat and altitude on oxygen uptake in sub-Antarctic weevils

Whole-organism oxygen uptake rate and its temperature sensitivity (determined using regression analyses and estimates of Q10) were examined in six closely related weevil species (Palirhoeus eatoni, Bothrometopus randi, Bothrometopus elongatus, Bothrometopus parvulus, Ectemnorhinus similis, and Ectemnorhinus marioni) from sub-Antarctic Marion Island over a short time period and using the same methods. Bothrometopus elongatus, B. parvulus, and the two Ectemnorhinus species have populations at both high and low elevations, and pairwise comparisons of these species were made. Regressions of the log of oxygen uptake rate on temperature and Q10 values revealed that the Ectemnorhinus species have a significantly greater thermal sensitivity than do species in the genera Bothrometopus and Palirhoeus. This may be considered an adaptation of the former to their moist lowland habitats and the requirements of angiosperm-feeding in E. similis. It is argued that elevated oxygen uptake rates and reduced slopes of the regression of the log of oxygen uptake rate on temperature in species and populations from high altitudes compared with those from low elevations provide evidence for metabolic cold adaptation. In addition, it seems likely that elevated oxygen uptake rates and their reduced thermal sensitivity within the genera Bothrometopus and Palirhoeus are an adaptation to the cold Neogene environments they evolved in. However, because data on the more basal taxa in the Ectemnorhinus group of weevils are not available, this temperature compensation could not be attributed conclusively to adaptation. Q10's of the lowland populations of all the species were negatively correlated with body water content, and it is suggested that the low temperature sensitivity of metabolism in P. eatoni and the Bothrometopus species may also be due to constraints imposed on them by their dry habitats.