Of fingers and thumbs and babies bums: The interacting effects of landscape structure and soil on the evolutionary radiation of 'stone plants' in the genus Argyroderma

I studied the interaction between landscape structure and edaphic habitat variation as drivers of evolutionary radiation in Argyroderma.; First I investigated the spatial scale of genetic differentiation and local adaptation within a single species. I found that neutral and adaptive genetic differentiation occurs between allopatric populations. Populations in independent drainage systems are genetically distinct, suggesting a history of restricted gene flow. Reciprocal transplant experiments showed that local adaptation occurs on one habitat type (the dense quartz habitat) only; resulting in adaptive divergence between allopatric populations on this habitat type, but not between populations on different habitat types within a drainage system. Local adaptation to soil microenvironments interacts with extrinsic and intrinsic restrictions to gene flow to generate the spatial structure of evolutionary divergence in A. pearsonii.; In the second chapter I show that morphological differentiation between coexisting species involves traits with potential functional importance in water stressed environments and that "sympatric" species occupy different edaphic microhabitats. Transplant experiments suggest that these species are locally adapted to the specific soils they occupy. I conclude that coexistence of Argyroderma species within drainage systems is facilitated by local adaptation of individual species to specific soil microhabitats and that the morphology-soil correlation in the genus likely reflects adaptive differentiation and not phenotypic plasticity.; The third chapter investigates the influence of landscape structure, soil and flowering time divergence on patterns of genetic and phenotypic differentiation across the full taxonomic and geographic range of the genus. I find evidence for strong spatial genetic isolation at all taxonomic levels. In addition, genetic differentiation occurs along a temporal axis, between sympatric species with divergent flowering times. Morphological differentiation occurs between populations occupying different edaphic microenvironments. Morphological differentiation is in turn significantly associated with flowering time shifts.; I thus propose that diversification within Argyroderma has occurred through a process of adaptive speciation in allopatry. Spatially isolated populations diverge phenotypically in response to divergent habitat selection which in turn leads to the evolution of reproductive isolation through divergence of flowering phenologies, perhaps as a correlated response to morphological divergence. Temporal divergence allows coexistence of previously isolated species following range expansion.