Date of Award
Ph.D. in Biological Science
Brice P. Noonan
Aaron M. Bauer
I explore how pre-Quaternary geoclimatic phenomena and geographical heterogeneity influenced sub-continental speciation processes and contemporary biogeographic patterns across the Southern Hemisphere, with particular focus on two regions that have experienced elevated levels of ongoing aridification – sub-Saharan (particularly Southern) Africa and Australia. I used standard methods from the molecular phylogeneticists’ toolbox (e.g. tree building using maximum likelihood and Bayesian approaches, haplotype networks, uncorrected p-distances) combined with environmental niche modeling, morphometric principal components and fossil calibrated molecular dating analyses in order to ascertain the role that Miocene geo-climatic events played in promoting lineage accumulation and diversification through time. I found a strong correlation between the formation of various local geologic features (e.g. the Drake Passage and the subsequent formation of the Antarctic Circumpolar Current; the Great Escarpment; Australia’s vast arid zone) and increased rates of diversification, ecological shifts into novel niches, and morphological evolution. I discovered high levels of unexpected cryptic diversity within an African endemic lineage of frogs that is linked to specific, local processes (habitat fragmentation and climatic stability). In contrast, I find little evidence to continue recognizing elevated diversity within a lineage of African agamid lizards. In both cases, I advocate for additional taxonomic attention in order to accurately estimate species diversity across southern Africa. I also discover novel phylogeographic barriers across the vast and largely understudied country of Namibia. Broadly, this work illustrates that global change affects local processes but that commonalities exist across broad latitudinal swaths. The affect of aridification promoted unique radiations within Australia and Africa, but can be traced to shared Miocene geo-climatic events. Genetics are a profound and effective way of tracing this geo-climatic signal, particularly in the Southern Hemisphere, which escaped much of the Plio-Pleistocene glacial cycles that erased such signal in the Northern Hemisphere.
Nielsen, Stuart Val, "The biotic effects of tertiary geoclimatic change in the southern hemisphere" (2016). Electronic Theses and Dissertations. 1350.