Publication Date

12-1-2001

Degree Program

Department of Biology

Degree Type

Master of Science

Abstract

The rock-dwelling cichlids (mbuna) of Lake Malawi have undergone an explosive evolution, giving rise to an assemblage of 300-500 species within the last one million years. Most widespread mbuna 'species' are characterized by the presence of local endemic populations, differing primarily in coloration and often of uncertain taxonomic rank. The recency and rapidity of speciation within the mbuna have led to difficulties in reconstructing an accurate species-level phylogeny, in turn limiting our ability to elucidate the evolutionary dynamics associated with divergence of coloration and other characters. Based on morphometric and meristic characters, Stauffer et al. (1997) erected a new genus along with ten new species. Here we use classical Mendelian analyses to investigate the inheritance and evolution of red dorsal fin coloration in Metriaclima thapsinogen and M. emmiltos, phenotypically similar taxa endemic to habitats separated by at least 350 km. Multiple crosses involving single males and four to five females were established in the laboratory. Crosses resulted in five F, broods and four F2 broods hybrid progeny (15-25 fry each), in addition to broods from control crosses. F, and F2 hybrid individuals were assessed for dorsal fin coloration while parental and F, hybrid individuals were evaluated, additionally, for eight meristic characters. Phenetic relationships among geographically similar morphs were assessed and compared to Stauffer et al. (1997) findings. Upon maturity, all hybrids showed red dorsal fin coloration. None of the eight meristic variables showed significant differences in means among parental, F, and control hybrid groups. Two meristic variables displayed significant fluctuating asymmetry in F, hybrids relative to parental and control groups, but this degree of asymmetry was less than predicted under a null model. UPGMA clustering resulted in M. thapsinogen and M. emmiltos grouping closer together than geographically proximate M. zebra. These data suggest the genetic basis for red dorsal fin coloration is allelic between M. thapsinogen and M. emmiltos, and are consistent with their evolution from a common red dorsal ancestor followed by lakewide dispersal. Alternative scenarios, including the existence of color and regulatory loci in each population and differential expression of a set of ancestral color polymorphisms are consistent with our findings.

Disciplines

Medical Sciences

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