The Cichlid fish of Lake Malawi provide a laboratory for evolutionary biologists to study the processes responsible for the origin of new species.  You have seen some of  the elements of this species rich system that make it so interesting to scientists on my Evolution of Malawi Cichlids page, but how can we exploit this system to learn more about the processes of evolution?  I am working on a number of projects focused on the Metriaclima zebra species complex of Lake Malawi in an attempt to discover the mechanisms that have resulted in their diversification.  The origin of new species occurs as populations of the same species diverge along their own evolutionary trajectories.  So a great way to study speciation is to study sibling species or populations of the same species to discover the forces acting to push them on their own evolutionary paths.  Below I will  briefly describe a few of the major things that I am working on to try to infer the evolutionary processes acting on  this species complex.

Male reproductive coloration in the M. zebra species complex:  convergence or vicarience?
Throughout Lake Malawi, several distinct populations of the typical M. zebra occur.  These populations of fish are essentially identical, except for a single feature of male reproductive coloration.  All males of some of these populations possess a blue dorsal fin, while all males of other populations possess a red dorsal fin.  Often a blue population will be within less than a kilometer from a red population.  This distribution presents an interesting question -- are populations that are geographically proximate more closely related to each other than distant populations, despite coloration?  Or, are all red dorsal populations more closely related to each other than they are to their blue dorsal fin bearing counter parts?  This question has more significance than it may seem at first.  These two color morphs are ecological analogs.  They apparently occupy the same ecological niche.  The fact that they never occur at the same locality is testament to this assertion.  If they are merely lake wide colonists of two lineages that diverged early on (i.e.., before the last low water stand) then why do they both still exist, and why in such close proximity to each other?  Is their distribution evidence that the divergence between red and blue forms has occurred several times within the lake, possibly with the aid of reproductive character displacement?  The answers to these questions have critical implications in both the timing and the mechanism of speciation in Lake Malawi.  If geographically proximate populations are genetically closest (convergence), the divergence (or speciation) of the groups would have to have occurred since the last low water -- less than 40,000 years ago.  This rate of speciation is exceedingly fast!  Similarly, if these populations have diverged in situ, there may be merit to the idea of sympatric speciation, or even speciation by sexual selection.  Alternatively, if red and blue populations are found to form two distinct clades (vicarience), slightly slower rates of diversification and standard allopatric divergence become more logical.  I am examining these relationships using several microsatellite DNA markers and calculations of genetic distance between populations.

A phylogeny for the zebras
Because of their extremely recent origin, the species of the M. zebra complex have been resistant to phylogenetic analyses.  As ecological analogs, they are morphologically identical.  While they differ in color, we know that color patterns are frequently convergent (as species of divergent genera often display very similar color patterns).  Attempts at phylogenetic analysis using mitochondrial DNA sequences have failed as a result of incomplete lineage sorting -- a  effect of the extremely young age of this group.  In the absence of a phylogeny, we have no way of making sister group comparisons which are critical to the evaluation of the speciation process.  We aim to reconstruct the phylogeny of this group using microsatellite DNA.  Microsatellites have generally been thought to be of no utility in interspecific comparisons.  Again, because of the recent origin of this group, we believe that microsatellites will be of use in erecting a phylogeny for this group.  Initial results indicate that microsatellites may be of use in this pursuit.

Field work in Lake Malawi
In October of 1998 I spent a month on Lake Malawi with my advisor, Dr. Irv Kornfield.  We spent much time observing the behavior of Cichlids in their natural habitat and the phenotypic variation within and between populations.  We also collected many fin clips for genetic analyses at home.  Field work was conducted with the assistance of Ad Konings, Martin Geerts, and Stuart Grantof Salima, Malawi. Below are some pictures of Lake Malawi.

Pictures Coming Soon....
 
 

This work on Malawi Cichlid fishes is supported by the National Science Foundation
NSF DEB 9707532