Abstract:
The malaria mosquito Anopheles gambiaes.s. is rapidly becoming a model for studies on the evolution of reproductive isolation. Debate has centered on the taxonomic status of two forms (denoted M and S) within the nominal taxon identified by point mutations in the X-linked rDNA region. Evidence is accumulating that there are significant barriers to gene fow between these forms, but that the barriers are not complete throughout the entire range of their distribution. The sampled populations from across Ghana and southern Burkina Faso, West Africa, from areas here the molecular forms occurred in both sympatry and allopatry. Neither Bayesian clustering methods nor FST-based analysis of microsatellite data found differentiation between the M and S molecular forms, but revealed strong differentiation among different ecological zones, irrespective of M/S status and with no detectable effect of geographical distance. Although no M/S hybrids were found in the samples, admixture analysis detected evidence of contemporary interform gene fow, arguably most pronounced in southern Ghana here forms occur sympatrically. Thus, in the sampled area of West Africa, lack of differentiation between M and S forms likely reflects substantial introgression, and ecological barriers appear to be of greater importance in restricting gene flow
