Recombination rate variation in mice from an isolated island

Abstract

Recombination rate is a heritable trait that varies among individuals. Despite the major impact of recombination rate on patterns of genetic diversity and the efficacy of selection, natural variation in this phenotype remains poorly characterized. We present a comparison of genetic maps, sampling 1212 meioses, from a unique population of wild house mice (Mus musculus domesticus) that recently colonized remote Gough Island. Crosses to a mainland reference strain (WSB/EiJ) reveal pervasive variation in recombination rate among Gough Island mice, including subchromosomal intervals spanning up to 28% of the genome. In spite of this high level of polymorphism, the genomewide recombination rate does not significantly vary. In general, we find that recombination rate varies more when measured in smaller genomic intervals. Using the current standard genetic map of the laboratory mouse to polarize intervals with divergent recombination rates, we infer that the majority of evolutionary change occurred in one of the two tested lines of Gough Island mice. Our results confirm that natural populations harbour a high level of recombination rate polymorphism and highlight the disparities in recombination rate evolution across genomic scales.

Keywords: island evolution; linkage map; recombination; recombination rate evolution.

Figure 1. Cross Design

Partially inbred lines of Gough Island mice were crossed with the wild-derived inbred strain WSB/EiJ. Four independent F₂ intercrosses were generated from these crosses.

Figure 2. Recombination rate differences between two lines of Gough Island Mice

Differences in recombination rate between two lines of Gough Island mice visualized as a gradient along chromosomes. Intensity of gradient from yellow to purple indicates greater relative recombination rate in Line A and Line B respectively. Plot markers with whiskers show center and range of 10, 25, and 50 Mb windows where recombination rates differ significantly (10% FDR).

Figure 3. Comparisons of recombination rates in Gough Island lines and the heterogeneous stock (HS)

A comparison of recombination rates using 25 Mb sliding windows in (A) the HS mice and Gough Line A, and (B) the HS mice and Gough Line B. Each point represents a single 25 Mb window with respective recombination rates along the x and y-axis. Windows that were significantly different between Gough Island Line A and Line B are highlighted in bold on these plots. (C) Squared difference in recombination rate between each Gough Island line and HS for these significantly different windows, showing substantially more dispersion from HS in Line A.