Population genetical evidence for host-race formation in Yponomeuta padellus

Abstract

The idea of speciation in sympatry (i.e., individuals of two diverging populations being physically capable of encountering one another with moderately high frequency), attracts increasing interest. Geographical barriers are usually considered to be a prerequisite for genetic differentiation and speciation. Many examples provided evidence for this allopatric speciation model strongly advocated by Mayr (1963). Nevertheless, two key observations supported the idea of sympatric speciation. First, the species richness of phytophagous insects in small isolated areas could not be explained purely by the allopatric model. Second, the shift of phytophagous insects onto introduced plants and the rapid adaptation to those hosts, resulted in the idea of sympatric speciation through host-race formation. Research into host races (i.e., populations of a species partially reproductively isolated from other conspecific populations as a direct consequence of adaptation to a specific host), therefore, plays an important role in discussing the probability of speciation in sympatry.