Post-Zygotic Isolation and Haldane’s Rule in Two Closely Related Lake Malawi Cichlid Species

Cichlid fishes from the Great Lakes in East Africa experienced an extensive, rapid, and recent diversification resulting in over 2,000 species of fish over the course of 10 million years. Such extraordinary diversification is thought to have been driven by behavioral pre-zygotic isolation. However, limited research has been conducted evaluating the role of post-zygotic isolation in promoting the reproductive isolation of African Cichlid fishes. In order to test the hypothesis that post-zygotic isolation contributes to the reproductive isolation of two closely related Lake Malawi African Cichlid fishes, Maylandia benetos and Maylandia zebra, I artificially created conspecific and reciprocal hybrid crosses and examined the fitness of the first generation. Fertilization rate, hatching rate, survival rate, and sex ratios were analyzed and compared. I found no differences in fertilization rate, hatching rate, or survival rate. However, the interspecific cross with a M. benetos female produced no male offspring. The absence of males in the interspecific cross with a M. benetos female may provide support for the hypothesis that post-zygotic isolation contributes to the reproductive isolation of M. benetos and M. zebra.