Climate change, wildlife trade, and the ecophysiological consequences of nocturnal vs. diurnal activity in lizards

Abstract

The nighttime environment is under multiple threats, from an asymmetric increase in night temperatures with climate change, to the disappearance of natural night light levels, to darkness-facilitated overexploitation of its biodiversity. In this PhD thesis, I demonstrate how important relevant spatio-temporal sampling and measurements are to understand diurnal and nocturnal responses to environmental change, with a particular focus on lizards. My thesis is divided into four data chapters. In my first data chapter I investigate the potential effect of diel variation on thermal tolerance measurements for six (diurnal, nocturnal, and cathemeral) species of geckos and skinks in Hong Kong and South Africa. I found that there is no consistent diel variation in thermal tolerance across species and activity patterns, but that each measurement of Ctmin and Ctmax should be context-dependent and diel variation should be accounted for in thermal tolerance assays. In my second data chapter, I used a laboratory thermal gradient to study selection of temperature in nocturnal and cathemeral lizards from Hong Kong across an entire diel cycle. I then applied a deep learning algorithm to track position of each lizard individually over time, from which I extracted body temperature and behavioural data. The results show that these nocturnal species do not display strong temperature selection nor variability in selection, but one species showed diel variation in voluntary thermal maximum. This finding emphasizes how observed temporal niches and thermal preferences can vary in complex ways that can challenge the prediction of ectotherm climate change responses. In my third data chapter I researched the availability of microclimates relevant to two syntopic species of lizards, one diurnal skink and one nocturnal gecko. I measured thermal tolerance of five populations of each species, experiencing different climates along a precipitation gradient in the Western Cape province of South Africa, and recorded hourly changes in operative temperature over a one-year period, for three types of microhabitats of choice. Using warming tolerance as a thermal vulnerability index and climate projections, I showed that the amount of buffering offered to each species is strikingly population-dependent, especially when accounting for microclimates and activity patterns. In my fourth and last data chapter, I investigated the trade in Tokay geckos found in the markets of Hong Kong and how that might impact wild populations. I compared the genetics (mtDNA gene) of populations of wild Hong Kong Tokays with i) dried Tokay geckos sold as Traditional Chinese Medicine (TCM), supplemented with stable isotope comparisons (d15N and d13C), and ii) sequences of the same gene from more locations available on GenBank. I found that TCM Tokay geckos sold in markets in Hong Kong did not originate from Hong Kong and that on at least two occasions, local populations likely grew as a result of introduction from Southeast Asia, probably through the pet trade. Throughout these four chapters, my thesis emphasizes how multi-facetted approaches and the incorporation of conservation physiology are needed to uncover consequences of multiple threats on biodiversity, and to determine pathways forward for effective management.