Phylogeography and thermal physiology of Meroles knoxii (Family: Lacertidae) : relevance for species responses to climate change

[摘要] ENGLISH ABSTRACT: Climate change is considered to be one of the greatest threats to species and ecosystems globally and is likely to contribute to the rapidly increasing number of species extinction. In South Africa, these climatic changes have been noted and are thought to persist. Lizards, as ectotherms, are exceptionally vulnerable to changes in their thermal environments and could face even greater extinction risk if they lack the capacity to behaviourally mediate or rapidly adapt to changing thermal environments. Species distribution models have only recently started incorporating genetic and physiological mechanistic variables to more accurately predict species responses to climate change. This study investigates genetic and physiological traits in order to elucidate genetic patterns and thermal traits that could aid in more accurately predicting the climate change responses of a southern African lacertid lizard. In Chapter 2, I investigated the phylogeographic occurrence of Meroles knoxii along the west coastal margin of southern Africa, with special focus on the southern mesic extent of the distribution range. Phylogeographic and population genetic analyses consistently retrieved three distinct genetic clades (north, central and south) that occur allopatrically on a north-south axis along the coastline. Body size differences occur between the northern and southern clades with the northern xeric clade displaying significantly larger body sizes than the southern mesic clade, suggesting local adaptation to these environments in conjunction with the genetic differentiation observed. The southern clade exhibited no genetic differentiation at a small spatial scale and is thus considered a single population. In Chapter 3, the thermal sensitivity of several traits of M. knoxii was investigated comparing two sites within the southern clade to determine whether and which traits are variable or conserved at a small spatial scale. Selected body temperatures differed significantly between sites. However, these differences are not considered biologically relevant in this study. Critical thermal limits, resting metabolic rate and total evaporative water loss did not differ significantly between sites and is considered a conserved thermal trait at this small spatial scale. In addition, the potential trade-off of thermal performance traits (sprint speed and stamina) was investigated for this ambush predator at one site, Zandvlei Nature Reserve. As expected, M. knoxii displayed optimal sprint speed capacity at high test temperatures and optimal stamina at lower test temperatures. This study aims to illustrate the importance of incorporating ecologically relevant mechanistic variables into species distribution models to more accurately predict species potential responses to future climate change.

[发布机构] Stellenbosch University