Thermal and metabolic physiology of New Zealand lizards

Abstract

New Zealand’s endemic lizards have speciated to fill nearly every available habitat type, and many species inhabit areas with low environmental temperatures. Unusually, from a global perspective, both lineages (geckos and skinks) include diurnally foraging and nocturnally foraging species. We review their physiology, focusing mainly on thermal and metabolic studies. Species that bask avidly, and those that bask cryptically, have field body temperatures (T b) averaging about 17-25°C on spring or summer days, with no individuals known to voluntarily exceed 34°C. Thermal performance curves for sprint speed have a typical asymmetric shape but are ‘left shifted’ compared with many species overseas. In particular, critical minimum and selected temperatures are relatively low, as expected for high-latitude species, and geckos have particularly left-shifted curves. Warm daytime temperatures enhance many physiological functions, including embryonic development and digestion. In general, metabolic rate also increases with T b, and metabolism alters (with no discernible pattern) in response to different acclimation temperatures. However, many species show thermal independence of metabolic rate over some range of temperatures, suggesting high metabolic stability; a relatively wide performance breadth also occurs in sprint speed. Nocturnally foraging species, which voluntarily emerge at low T b (sometimes ≤10°C), have physiological adaptations that enhance performance, including a low energetic cost of locomotion, but may have relatively high rates of cutaneous water loss. As a group, New Zealand’s lizards function well at low temperatures, and the warmer temperatures that climate change will bring may enhance some aspects of their physiological function.