Allopatric and sympatric modes of speciation: examples from Drosophila

Basically, there are two different ways by which new species are created: anagenesis and cladogenesis (true speciation). During anagenesis, one species is transformed into new one so there is a phyletic change in the course of time and there is no involvement of reproductive isolation. Cladogenesis is considered as true speciation during which new species originate through splitting of pre-existing ones. Different models have been proposed from time to time to explain the modes of speciation. There are two important modes of speciation which are primarily based on geographic factors: allopatric (dichopatric and peripatric) and sympatric. In this article, both allopatric and sympatric modes of speciation are briefly described with the help of suitable examples from Drosophila.