Date of Award
Program or Major
Doctor of Philosophy
Thomas D Kocher
East African cichlids are a paramount example of adaptive morphological radiation. The most dramatic difference among species occurs in oral jaw design and correlates with ecological niche partitioning. Convergent evolution of trophic forms between lakes suggests a common mechanism. What combination of intrinsic and extrinsic factors constitute this mechanism still remains to be seen. The goal of this dissertation was to examine the genetic basis of shape differences between two closely related cichlid species that employ alternate modes of feeding. This was achieved through a number of independent experiments. First, I used field data to characterize the way in which foraging habitat was partitioned between sympatric rock-dwelling species from Lake Malawi. Second, morphological differences between two species that employ alternate modes of feeding, Labeotropheus fuelleborni and Metriaclima zebra, were quantified via geometric morphometrics. I found that specific aspects of shape predicted differences in feeding performance. In this experiment I also developed the phenotypic characters that were used in subsequent experiments. Next, the genetic bases of these morphological characters were biometrically estimated using the Castle-Wright estimator. I estimated between 1 and 11 factors to control shape differences in various traits. Specific traits were also shown to segregate together in hybrid progeny, suggesting a degree of pleiotropy among genes that underlie differences in the cichlid feeding apparatus. Finally, I constructed a genetic linkage map for Lake Malawi's rock-dwelling cichlids, and identified quantitative trait loci (QTL) that affected shape differences in the cichlid head. Segregation at 136 molecular markers was studied in 173 F2 hybrids. The final linkage map consisted of 126 markers distributed over 24 linkage groups and 838 cM. QTL were detected for sex, color, and 15 morphological traits that distinguish the shape of the feeding apparatus in L. fuelleborni and M. zebra. At every stage of this dissertation results are related to the developmental and functional biology of the cichlid head.
Albertson, Richard Craig, "Genetic basis of adaptive radiation in East African cichlids" (2002). Doctoral Dissertations. 98.