The New Zealand common gecko Hoplodactylus maculatus: an ecophysiological comparsion of two isolated populations

Abstract

Thermophysiological traits of two isolated Hoplodactylus maculatus populations were investigated to test adpatations to climate. Geckos were collected from Craigieburn (high altitude, generally cooler site) and Banks Peninsula. If climatic conditions at respective sites influenced physiology, I expected geckos from Craigieburn to exhibit cold-adapted physiological traits, whilst Banks Peninsula geckos would exhibit traits more characteristic of a warmclimate species. To this end I investigated four thermophysiological parameters: metabolism (SMR), preferred body temperature (PBT), locomotory performance and critical thermal minimum (CTMin). I hypothesized that if climate had an effect on SMR, Craigieburn geckos would exhibit higher levels of SMR which typically characterise other coolclimate reptiles. Craigieburn geckos displayed an average relative elevation of SMR over Banks Peninsula geckos of 26%. Furthermore, Craigieburn geckos appeared to be 'geared' towards lower body temperatures and exhibited a greater acclimatory and acclimatizatory ability of SMR. The PBT of Craigieburn geckos was consistently elevated above Banks Peninsula geckos. This finding was somewhat paradoxical in light of previous studies of this parameter. A closer examination of the ecology of the two populations is required to clarify the adaptive significance of a higher PBT in geckos from a cooler climate. With respect to locomotory performance, I hypothesized that if thermal extremes influenced activity, Craigieburn geckos would exhibit activity patterns which help ameliorate the adverse effects of cold temperature. Craigieburn geckos did in fact have greater independence of activity to temperature than Banks Peninsula geckos, especially over lower body temperatures. The final parameter investigated, that of the critical thermal minimum, failed to distinguish the populations decisively. However there was some evidence of a greater acclimatizatory and acclimatory range in Craigieburn geckos, providing somewhat limited support for a population difference. Investigations into all four parameters lead me to conclude that populations of Hoplodactylus maculatus from Craigieburn and Banks Peninsula are physiologically distinct and warrant a revision of nomenclature.