DNA variation at the rp49 gene region in Drosophila madeirensis and D-subobscura from Madeira: inferences about the origin of an insular endemic species

An similar to1.6-kb fragment spanning the rp49 gene was sequenced in 16 lin es of Drosophila subobscura from Madeira and in 22 lines of the endemic spe cies D. madeirensis. Nucleotide diversity in D. subobscura from Madeira (pi = 0.0081) Introduction was similar to that in lines from Spain carrying th e O3+4 chromosomal arrangement (pi = 0.0080). No significant genetic differ entiation was detected between insular and continental O3+4 lines of D. sub obscura. These results are compatible both with a rather recent and massive colonization, and with multiple colonization events from the continent. Nu cleotide diversity in D. madeirensis (pi = 0.0076) was Similar to that in D . subobscura, which deviates from the expectation, under strict neutrality, of a lower level of variation in an insular species with a small populatio n size. The observed numbers of shared polymorphisms and of fixed differenc es between D. madeirensis and D, subobscura are compatible with the isolati on model of speciation, where shared polymorphisms are due to common ancest ry.