On the origin of Lake Malawi cichlids and mechanisms of their maintenance.

A fundamental task of evolutionary biology is to explore patterns of speciation. Evolutionary biologists have been intrigued for centuries by the fact that some species underwent extensive radiation while others diversified little. Speciation rates can be influenced by both ecological and lineage specific factors. However, a comprehensive understanding of how these factors operate on speciation is limited. Speciose communities, like the cichlids in the East African Great Lakes, offer unique opportunities to examine these factors. In this study I integrated ecological, behavioral and evolutionary genetics to investigate the mechanisms that govern the speciation and coexistence of Lake Malawi cichlids. First, I examined the genetic architecture of male coloration and female mate choice through quantitative genetic analyses. This study revealed that 1) male color pattern is polygenic, 2) female mate choice, however, may be controlled by a small number of genes. Furthermore, a joint analysis of color pattern and female mate choice suggests that genetic linkage between these two traits is unlikely. However, the simple genetic architecture of female mate choice can only partially explain the cichlids speciation. By testing the role of Prostaglandin F2α (PG) in cichlid female mate choice, I found that female mate choice can be invoked by the administration of PG. The molecular genetic mechanism of cichlids speciation was investigated through quantitative genetic mapping. I identified several putative quantitative trait loci (QTL) controlling male color pattern. Interestingly, genes that control the color of male body bar and pelvic fin seemed to be a pair of paralogs. However, I was unable to identify the loci associated with female mate choice. Finally, ecological mechanism of species coexistence was investigated. I found that habitat complexity predicts species and functional diversity of the cichlids communities: a higher rugosity allowed more species and functional groups to coexist.