Mapping of within-species segregation distortion in Drosophila persimilis and hybrid sterility between D. persimilis and D. pseudoobscura

Abstract

In contrast to the prevailing dogma in the 1990s, recent studies have suggested that an evolutionary history of segregation distortion within species may contribute to sterility in species hybrids. However, this recent work identified segregation distortion exclusively in species hybrids that may never have had an evolutionary history of segregation distortion in either parent species. We expand on previous work using a strain of Drosophila persimilis exhibiting segregation distortion within species to generate QTL maps for segregation distortion and hybrid sterility in crosses between D. persimilis and D. pseudoobscura. The maps localize regions along the XR contributing to both phenotypes, and they indicate one region of overlap between the two maps. This overlap could provide preliminary evidence for an association between segregation distortion within species and hybrid sterility, but the localizations are currently too broad to have confidence in this conclusion. This work is a first step towards possibly supporting a genetic conflict model of speciation in this system.

Figure 1

Orientation of inversions and location of markers along XR. (A) Arrows indicate the orientation of the inversion, located from band 26D to band 38 on the D. pseudoobscura polytene chromosome (images of chromosomes adapted from Figures 8 and 9 of Schaeffer et al. (2008), with permission from Genetics Society of America). SR D. persimilis and Standard (nonSR) D. pseudoobscura are homosequential for the XR inversion, while Standard D. persimilis carries a unique arrangement. (B) The XR of D. pseudoobscura was used to map the marker locations, given its better coverage and annotation (Schaeffer et al. 2008). Markers represented only three of the eight scaffolds (group 6, group 8a, and group8b), since our work focused on the region carrying the inversion. The marker locations are indicated to scale based on the physical location; the recombination distance (cM) indicated between each marker is based on our sterility map results.

Figure 2

Crossing scheme to map sterility and segregation distortion on the X chromosome. Long boxes indicate X chromosomes, and short boxes indicate the Y chromosome (autosomes are not shown). The crosses for sterility (A) and segregation distortion (B) both start by crossing D. pseudoobscura white (white) to SR D. persimilis SCI (black). F₁ hybrid females are then either backcrossed to D. pseudoobscura white for the sterility cross, or crossed to D. persimilis MSH1993 (gray) for the distortion cross. The resultant males are then backcrossed to their respective paternal species, and sex ratios of their progeny are counted.

Figure 3

QTL map of segregation distortion on the D. persimilis SCI XR. Map was generated using Composite Interval Mapping (CIM) of BCper males producing 15 or greater progeny. Significance threshold (LOD 1.5) was calculated by 1000 permutations, shown as the horizontal line. Marker locations are indicated with solid gray arrowheads.

Figure 4

QTL map along XR of hybrid sterility between SR D. persimilis SCI and D. pseudoobscura white. Map was generated using Composite Interval Mapping (CIM) of BCps males with ps genotypes at XL and 2^nd chromosome inversions. Significance threshold (LOD 1.5) was calculated by 1000 permutations, shown as the horizontal line. Marker locations are indicated with solid gray arrowheads.