Several recent population-level studies of mitochondrial DNA (mtDNA) variation in Tanganyikan cichlid fishes illustrate the strength and utility of mtDNA analysis as a powerful tool in evolutionary biology. This chapter attempts to show that these studies also contain information about the various levels of biodiversity that are relevant for the identification of "evolutionary significant units" (ESUs) and the assessment of conservation priorities of cichlid taxa or areas from an evolutionary perspective. These results based on mtDNA studies on cichlid populations are consistent with the notion that species should never be viewed as undifferentiated monotypic entities. The presence or absence of genetically and geographically distinct populations is an important feature that characterizes each of these species, and is important to consider when arriving at informed conservation or management decisions.
Mitochondrial DNA studies have also provided new information on the distributional boundaries of some genetically divergent cryptic species, a conclusion that, in a number of examples, has been supported by the subsequently discovery of morphological and behavioural differences. It is possible that there may be many more undiscovered cases of allopatrically occurring morphologically similar fishes that are erroneously considered to be conspecific.
The phylogeographical results indicate that closely related cichlids can have markedly
different within-lake distribution ranges, a conclusion that has major implications in
any efforts towards the conservation of the Tanganyikan rock-dwelling cichlid fauna.
Provided that concordant lines of evidence are found for historical centres of biodiversity
in Lake Tanganyika, emphasis should be placed on preserving the integrity of such regional
biotas by establishing regionally structured protected sanctuaries. Logistic considerations
may make it impossible to preserve the genetic diversity in all components of the cichlid
fauna by such measures. However, to formulate guidelines for the establishment of protected
areas within Lake Tanganyika, and for the management of the faunas that these areas harbour,
genetic information can be a very useful complement to zoogeographical data that is based
solely on traditional morphologically based species descriptions.