A revision of the genus Melanochromis (Teleostei: Cichlidae) from Lake Malawi, Africa, using morphological and molecular techniques
The taxonomy and systematics of Melanochromis, a rock-dwelling genus of cichlid from Lake Malawi, Africa, were evaluated using morphological and molecular techniques. Ten new species of Melanochromis were described and the validity of five previously described species was examined. An artificial, dichotomous key based primarily on adult coloration and meristics was developed. The evolutionary history of the genus was reconstructed using morphological data, allozyme data, and mitochondrial DNA (mtDNA) sequence variation, and congruence among the phylogenies evaluated.
Specimens representive of each recognized species of Melanochromis were collected and detailed color notes were made on live individuals. Standard morphometric and meristic measures were collected and analyzed using sheared principal component, discriminant function, and canonical correlation analyses. Sheared principal component analysis assisted in discrimination among species on the basis of shape and meristics, without the confounding influence of size. Relationships among species were examined based on overall phenetic similarity, and phylogenetically using discrete coding of continuous morphometric and meristic data. Results suggest phenetically similar species were not necessarily the most closely related phylogenetically.
Variation of nuclear markers, which was assessed using protein electrophoresis, was low. Allele frequencies were heterogeneous among species, but no fixed allelic differences were observed. The amount of phylogenetic information was limited and reconstruction of phylogenies based on these data lacked statistical validity. The low protein divergence among Melanochromis species is consistent with protein surveys of other species of Lake Malawi cichlids and support recent speciation events within this genus.
Analysis of mtDNA sequence variation in the rapidly evolving D-loop region revealed low genetic diversity within Melanochromis and little or no population-level sequence divergence was observed. Seventy-five percent of the populations in which multiple individuals were examined were fixed for a single mtDNA haplotype and sequence divergence within species ranged from 0 to 1.13%. Between congeneric species, sequence divergence ranged from 0 to 2.5%. Shared mtDNA haplotype between valid species further supports the recency of species divergence within this genus.
Hypotheses generated concerning the relationships among Melanochomis species
indicate that similar morphologies and color patterns have arisen several times within
the genus. Testing of these hypotheses, however, will have to await the development
of independent, polymorphic genetic markers.