Date of Award

12-2002

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Advisor

Irv Kornfield

Second Committee Member

William Glanz

Third Committee Member

Thomas Kocher

Abstract

The cichlid fish species flocks of East Africa provide a compelling model system in which to study the process of speciation. In Lake Malawi, greater than 1000 species of cichlids have emerged since the filling of the lake basin about 1 million years ago. Over 99% of the Lake Malawi haplochromine cichlids are endemic, suggesting that most of this diversification has taken place within the temporal and spatial boundaries set by the Lake's shores. Moreover, many of these species are endemic to small areas within the lake, indicating that speciation has occurred very recently or perhaps is in progress in some instances. Examination of the genetic structure of recently divergent populations or species is relevant to our understanding of the process of speciation in general. Here I present work on several populations, insipient species and species of Lake Malawi haplochromine cichlids. I have examined the genetic diversity of microsatellite DNA markers and applied these data to specific hypotheses relating to speciation. First I review the literature relevant to the latter chapters. Chapter two is an examination of several populations with two distinct color patterns and lake-wide distributions. This chapter contributes genetic data to a persistent biogeographical problem among these fishes - monophyly of color pattern versus independent derivation of similar pattenls in disparate portions of the lake. This work showed that many like-colored populations share genetic similarity, but one population likely represents parallel evolution of coloration. In chapter 3, I present genetic data that suggests that hybridization has occurred among closely related species differing in coloration. These data contribute to a growing list of confinned and suspected cases of hybridization among African cichlids, and is the first genetic data supporting hybridization among congeners in Lake Malawi. Finally, I present a microsatellite phylogeny of several populations and newly derived species. This examination confirmed conclusions from chapter two, that color convergence is a common phenomenon among Lake Malawi cichlids. Indeed several characters of coloration evolved multiple times among the taxa examined. This dissertation contributes several new findings to the field of speciation among African cichlids, though many questions remain. While it is unlikely that a single mechanism is responsible for generating this remarkable species diversity, revealing the conditions that have allowed the cooperation of multiple mechanisms will be a fascinating advance in the study of evolution.

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