Sympatric differentiation and speciation: Insights from drosophila studies

One can hardly find a more controversial issue in evolution biology than species concept. Inside this widely debatable area, the most discussable questions concern the driving forces of population differentiation and the role of geographical isolation as a factor of species divergence (allopatric vs. sympatric scenarios). Here, we review the main influential theoretical works and experimental evidence regarding the validity of sympatric model. We also present our empirical data on extensive studies of interslope genetic divergence of Drosophila at Nahal Oren canyon (Mount Carmel, Israel). Our results suggest that populations inhabiting opposite slopes exemplify ongoing divergence taking place regardless of high migration. For a long time, sympatric speciation was considered possible, but an extremely rare event that can hardly be observed or proved. S. Via found a precise image-bearing expression for the sympatric model: "The Ugly Duckling."