Behavior and Genetics Determining Hybridization: Studying Xiphophorus malinche and birchmanni at the Calnali and Tlatemaco hybrid zones in Mexico

Abstract

Very broadly, hybridization and speciation are important processes in evolutionary biology. During and after speciation, species can hybridize; in some cases, hybrids are fertile and viable but, in others, they suffer from hybrid incompatibilities. Specifically, in the Xiphophorus genus, X. birchmanni and X. malinche exhibit different hybridization patterns in distinct regions. At the Calnali and Tlatemaco hybrid zones in Mexico, distinct hybrid zone structuring is found at each location: more structured hybrid zones are typical at Calnali, while unstructured hybrid zones (with more hybrids) are found at Tlatemaco. After performing multiple experiments, I have concluded that the most likely explanation for this distinction in hybrid zone structuring is not natural or sexual selection but hybrid incompatibility (detected through the signature of linkage disequilibrium or LD). The differences in Xiphophorus hybrid incompatibility between the two rivers disfavor hybridization at Calnali and allow hybridization at Tlatemaco. Future research should focus on understanding why these differences have arisen. Although environmental factors seem to be at play, there is also a possibility that random processes may be important components in generating LD.