Evolution of diversity in African frogs (Arthroleptis and Cardioglossa)

The diversity of extant amphibians is staggering, yet the evolutionary history of many diverse lineages remains unknown. The goal of this thesis is to document and interpret patterns of diversity in a speciose lineage of frogs restricted to sub-Saharan Africa. Despite having a broad range of organismal diversity, little is known of the evolution of African amphibians. I focus on two genera, Cardioglossa and Arthroleptis , which together comprise more than 50 species distributed throughout diverse habitats of sub-Saharan Africa from Senegal to Kenya to eastern South Africa. These genera exhibit two life history strategies, a four-fold range of adult body size, and diverse morphologies. Phylogenetic relationships among Arthroleptis and Cardioglossa species were estimated based on analysis of mitochondrial DNA sequences using parsimony, likelihood, and Bayesian methods. The most recent common ancestor of Arthroleptis was miniaturized and had direct development. These features may have facilitated the ecological and geographic expansion of this lineage from the forests of Central Africa into diverse habitats in western, eastern and southern Africa.

These genera exhibit extreme sexual dimorphism in third finger length, which is unique among vertebrates. Males have relatively longer fingers than females and growth in these fingers exceeds that of their other fingers and of female third fingers. Loss or reduction of male traits occurred independently in both genera. Rejection of simple hypotheses of character evolution suggests that changes in sexual selection forces may be responsible for driving diversity. Miniature species exhibit novel patterns and skeletal elements not found in related species. These miniature species are morphologically similar, but are not a clade. Instead, some morphologies may have evolved convergently in different miniature lineages. Still others may have evolved concomitant with miniaturization but were then lost when the lineage attained larger body sizes. Discovery of a new species of Cardioglossa from Mt. Manengouba in Cameroon prompted a study of diversity in this genus. Multivariate ordination techniques were used to determine patterns of morphological diversity. Historical continuity of Africa's montane faunas is supported by similarity between a single species restricted to the Albertine Rift Mountains and several species restricted to the mountains of Cameroon.