Intrinsic post-zygotic isolation and Haldane’s rule in Lake Malawi cichlids.


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To assess the intrinsic fitness of hybrids and test for the action of Haldane’s rule of two closely related Lake Malawi cichlid species, Maylandia benetos and M.zebra, fitness-related traits, sex ratios and sex-linked microsatellite loci were measured or genotyped in offspring from both conspecific and interspecific crosses. No differences were found between hybrid and non-hybrid offspring in fertilization, hatching and survival rate. There was no difference in sex ratio between the interspecific and conspecific crosses with M.zebra female. By contrast, males were absent in the interspecific cross with M. benetos female. The microsatellite data showed that M. benetos have an XY sex determination system. The gender of hybrids from both reciprocal crosses was determined by the allele they inherited from their M. benetos parental, suggesting a dominance effect of sex determination system in M. benetos to that in M. zebra.



Cichlids. Post-zygotic isolation. Sex determination system. Haldane's rule.