Sex-specific recombination landscape in a species with holocentric chromosomes

The rate and chromosomal positioning of meiotic recombination significantly affects the distribution of the genetic diversity in eukaryotic genomes. Many studies have revealed sex-specific recombination patterns, with male recombination typically biased toward chromosome ends, while female recombination is more evenly distributed along chromosomes, or concentrated near the chromosome center. It has been proposed that such pattern in females may counteract meiotic drive caused by selfish genetic elements near centromeres and should not occur in species devoid of clearly defined centromeres, but evidence for the latter is scarce. Here, we constructed a sex-specific genetic map of a species with holocentric chromosomes, the bulb mite ( Rhizoglyphus robini ), a sexual selection model with alternative male reproductive phenotypes. We found a similar recombination landscape in both males and females, with a consistent pattern of increased rates towards both chromosome ends, and higher recombination rate in females than in males. A region on chromosome 7, carrying a high density of markers associated with the expression of alternative male reproductive phenotypes, was among several regions with particularly low male recombination rate. We detected a positive correlation between the recombination rate and the repeat density (highest at chromosome ends), and negative correlation with the gene density (peaking at chromosome centers). Our results are consistent with the meiotic drive hypothesis and suggest that recombination evolution is closely linked to the chromosome features.