A microsatellite linkage map for Drosophila montana shows large variation in recombination rates, and a courtship song trait maps to an area of low recombination

Abstract

Current advances in genetic analysis are opening up our knowledge of the genetics of species differences, but challenges remain, particularly for out‐bred natural populations. We constructed a microsatellite‐based linkage map for two out‐bred lines of Drosophila montana derived from divergent populations by taking advantage of the Drosophila virilis genome and available cytological maps of both species. Although the placement of markers was quite consistent with cytological predictions, the map indicated large heterogeneity in recombination rates along chromosomes. We also performed a quantitative trait locus (QTL) analysis on a courtship song character (carrier frequency), which differs between populations and is subject to strong sexual selection. Linkage mapping yielded two significant QTLs, which explained 3% and 14% of the variation in carrier frequency, respectively. Interestingly, as in other recent studies of traits which can influence speciation, the strongest QTL mapped to a genomic region partly covered by an inversion polymorphism.

The genetic architecture of sexually selected traits in two natural populations of Drosophila montana

“…The simulated trait effect size was based on a QTL detected for song variation in crosses between North American and Finnish D. montana (Colorado and Oulanka, that is, a different population from North America) Schafer et al, 2010;Lagisz et al, 2012). We failed to detect QTL for the same traits and genomic positions as the between-population study.…”

“…We compare the within-population QTL analysis of song variation with previous work that identified QTL influencing courtship song by using between-population outbred crosses of D. montana (from Oulanka, Finland and Colorado, N. America). The detected QTL were on two chromosomes (X and 2) and one candidate gene was potentially associated with each QTL (per and fru, respectively) (Schafer et al, 2010;Lagisz et al, 2012), although it has not been confirmed whether these or other genes under the peaks are responsible for the phenotypic effects.…”

Two distinct genomic regions, harbouring the period and fruitless genes, affect male courtship song in Drosophila montana

“…We worked on a cross between two strains described in Schäfer et al (2010) known to be divergent for song characters. The two genetically variable isofemale strains representing natural populations from Finland (Oulanka, O3F66) and from the USA (Colorado, C3F13) were kept under laboratory conditions for approximately 1 year before crossing.…”

“…Earlier studies revealed significant differences in several song characters, wing shape and genital morphology, between populations from distinct geographic regions (Suvanto et al, 2000;Klappert et al, 2007;Routtu et al, 2007). The identification of polymorphic microsatellite markers in D. montana has led to the construction of a linkage map and to the mapping of QTL for song carrier frequency (FRE) differences between populations (Schäfer et al, 2010). The largest QTL mapped to an area of low recombination, containing many loci.…”

“…Specific objectives of this study were the following: (1) to develop genetic markers within candidate genes for song characters in D. montana; and to add them to the microsatellite linkage map described in Schäfer et al (2010); (2) to include data on five additional song characters; and (3) to identify and describe QTLs responsible for the divergence of courtship song between two strains originating from natural populations in order to elucidate the genetic architecture of a complex quantitative trait. More generally, we aim to compare the results obtained with published results on QTL in the other species from the D. virilis group.…”