Geographic Dispersal and Clonal Diversity in Unisexual Fish Populations

Publisher Website
Google Scholar
Abstract
Tissue grafting was used to investigate clonal diversity in populations of the unisexual hybrid fish, Poeciliopsis monacha-occidentalis from 5 rivers in northwest Mexico. The ranges of the 2 sexual progenitor species, P. monacha and P. occidentalis, overlap only in the southernmost of these rivers. Synthesis of new clones of P. m.-occidentalis via interspecific matings may still occur there. The other 4 rivers are north of the range of P. monacha, but contain populations of P. m.-occidentalis and its sexual host species, P. occidentalis. A surprisingly large number of clones was detected in the southernmost river. Unisexual strains descended from 33 wild-collected females comprised 17 distinct clones. Clonal diversity was drastically lower in the northern rivers. In 1 river 2 clones were detected; the other 3 rivers had only 1 clone each. Multiple-hybrid origins may be the most important source of clonal diversity in P. m.-occidentalis. Evolution does not cease with the advent of unisexuality. An example of genetic change in unisexuals subsequent to their hybrid origin was detected. The single clone from the northernmost river contains unique alleles at 2 electrophoretic loci. This clone was antigenically similar to the single clone from the adjacent river. These 2 clones probably have diverged genetically from a common ancestral clone that originated in the south. Factors affecting the clonal composition of populations were discussed. The clonal composition of the populations is not due to random processes. Among the selective forces influencing clonal diversity, habitat complexity probably plays a minor role in comparison to the high degree of temporal instability which is characteristic of these desert stream habitats.