THE INFLUENCE OF HABITAT AND ALTITUDE ON OXYGEN-UPTAKE IN SUB-ANTARCTIC WEEVILS

Whole-organism oxygen uptake rate and its temperature sensitivity (det ermined using regression analyses and estimates of Q(10)) were examine d in six closely related weevil species (Palirhoeus eatoni, Bothrometo pus randi, Bothrometopus elongatus, Bothrometopus parvulus, Ectemnorhi nus similis, and Ectemnorhinus marioni) from sub-Antarctic Marion Isla nd over a short time period and using the same methods. Bothrometopus elongatus, B. parvulus, and the two Ectemnorhinus species have populat ions at both high and low elevations, and pairwise comparisons of thes e species were made. Regressions of the log of oxygen uptake rate on t emperature and Q(10) values revealed that the Ectemnorhinus species ha ve a significantly greater thermal sensitivity than do species in the genera Bothrometopus and Palirhoeus. This maybe considered an adaptati on 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 oxyge n uptake rate on temperature in species and populations from high alti tudes compared with those from low elevations provide evidence for met abolic cold adaptation. In addition, it seems likely that elevated oxy gen uptake rates and their reduced thermal sensitivity within the gene ra 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 tem perature compensation could not be attributed conclusively to adaptati on. Q(10)'s of the lowland populations of all the species were negativ ely correlated with body water content, and it is suggested that the l ow temperature sensitivity of metabolism in P. eatoni and the Bothrome topus species may also be due to constraints imposed on them by their dry habitats.