Variable thermal tolerance breadths within South African lizard species across a rainfall gradient
Ms Pauline Dufour1, Dr Timothy Bonebrake1, Dr Susana Clusella-Trullas2
1The University Of Hong Kong, Hong Kong, Hong Kong, 2Stellenbosch University, Stellenbosch, South Africa
Climate change is a global and complex phenomenon whose consequences vary greatly from one bioclimatic zone to another. The west of South Africa has experienced more frequent and longer droughts in recent years, while the east has seen flooding at the same time.
Widespread species experience different environmental conditions across their distribution, therefore offering a good case study for understanding the potential for physiological adaptations to a changing climate. In the Western Cape, the same species can be found across hundreds of kilometres, from Mediterranean climates (high annual precipitation) to Karoo-dry sites (low annual precipitation). During the austral spring 2018, we sampled three populations of two co-occurring species of geckos and skinks (Chondrodactylus bibronii and Trachylepis variegata respectively) and measured thermal tolerance (Ctmin and Ctmax) under laboratory conditions.
We found that Ctmax was not significantly influenced by the location of the population on the rainfall gradient but Ctmin was different across locations. Counter to expectations, populations exhibited a lower Ctmin (i.e. greater thermal tolerance breadth) in the drier sites. Moreover, we found no notable difference in mass of individuals from different locations with variable precipitation levels.
Our findings seem to indicate that lizard populations in ecosystems with higher levels of precipitation (also sites with greater productivity or abundance of resources) are thermal specialists relative to their dry-adapted counterparts. As the frequency and intensity of extreme climatic events increase, the interplay between precipitation/resource levels and temperature/thermal tolerance will likely be critical in understanding ectotherm species redistribution and responses to climate change.
Pauline Dufour is investigating effects of climate change on nocturnal ectotherms for her PhD at the University of Hong Kong. Conservation physiology and environmental gradients led her to South Africa where her project (hosted by Stellenbosch University) aims at comparing intra specific variations in thermal ecology in relation to precipitation and resource-use.