Phylogeographic patterns in Drosophila montana

P. MIROL; M. SCHAEFFER; L. ORSINI; J. ROUTTU; C. SCHLOETTERER; A. HOIKKALA; R. BUTLIN

MOLECULAR ECOLOGY

Año: 2007 vol. 16 p. 1085 - 1097

0962-1083

The Drosophila virilis species group offers valuable opportunities for studying the roles ofchromosomal re-arrangements and mating signals in speciation. The 13 species are dividedinto two subgroups, the montana and virilis ‘phylads’. There is greater differentiationamong species within the montana phylad in both karyotype and acoustic signals thanexists among members of the virilis phylad. Drosophila montana is a divergent specieswhich is included in the montana phylad. Here, we analyse the phylogeography ofD. montana to provide a framework for understanding divergence of acoustic signals among populations. We analysed mitochondrial sequences corresponding to the cytochrome oxidase I and cytochrome oxidase II genes, as well as 16 microsatellite loci, from 108 lines ofD. montana covering most of the species’ range. The species shows a clear genetic differentiationbetween North American and Scandinavian populations. Microsatellite allele frequenciesand mitochondrial DNA haplotypes gave significant FST values between populations fromCanada, USA and Finland. A Bayesian analysis of population structure based on themicrosatellite frequencies showed four genetically distinct groups, corresponding to thesethree populations plus a small sample from Japan. A network based on mitochondrialhaplotypes showed two Finnish clades of very different shape and variability, and anotherclade with all sequences from North America and Japan. All D. montana populations showed evidence of demographic expansion but the patterns inferred by coalescent analysis differed between populations. The divergence times between Scandinavian and North American clades were estimated to range from 450 000 to 900 000 years with populations in Canada and the USA possibly representing descendants of different refugial populations. Long-term separation ofD. montana populations could have provided the opportunity for differentiation observed in male signal traits, especially carrier frequency of the song, but relaxation of sexual selection during population expansion may have been necessary.