Abstract:
Temperature is key to ectotherm physiological function and thus drives evolution and impacts
ecological niches. Anthropogenic climate change will lead to increased drought, temperature and extreme weather events and thus may lead to species-wide extinction events. We wanted to explore if there was thermal plasticity of thermal sensitivity of the metabolic rate and cuticular water loss (CWL) within and between seven species of New Zealand stick insect, using two different acclimation
treatments of 10°C and 20°C, across five trial temperatures of 5°C, 10°C, 20°C, 30°C and 35°C. We also wanted to determine if there was evidence to support the metabolic cold adaptation hypothesis and the desiccation adaptation hypothesis. We used flow-through respirometry to record the metabolic rate and CWL of seven New Zealand stick insect species. Thermal performance curves were used to
visualise the metabolic rate and CWL. The ANOVA of mixed linear models were used to test for statistical significance within and between stick insect species. We found that there was no thermal plasticity for the thermal sensitivity of metabolic rate and cuticular water loss for all of the seven
species. There was thermal plasticity for the overall metabolic rate for Acanthoxyla prasina, Clitarchus
hookeri and Micrarchus nov. sp. 2, where the 10°C acclimation treatment was higher for A. prasina
and C. hookeri and the 20°C acclimation treatment was higher for M. nov. sp. 2. Further, there were strong phylogenetic correlations between the metabolic rate and the CWL between all of the species,
except for M. nov. sp. 2, which showed evidence for convergent evolution of metabolic rate. Lastly, it
was also found that Spinotectarchus acornutus likely does not have adaptations to conserve CWL and that Micrarchus hystriculeus does. We conclude that there is evidence to support the cuticular
adaptation hypothesis but not the metabolic cold adaptation hypothesis. Both the low latitude subtropical stick insects and the high-latitude temperature stick insects are expected to be impacted by anthropogenic climate change.
