No Evidence that Infection Alters Global Recombination Rate in House Mice.

Recombination rate is a complex trait, with genetic and environmental factors shaping observed patterns of variation. Although recent studies have begun to unravel the genetic basis of recombination rate differences between organisms, less attention has focused on the environmental determinants of crossover rates. Here, we test the effect of one ubiquitous environmental pressure-bacterial infection-on global recombination frequency in mammals. We applied MLH1 mapping to assay global crossover rates in male mice infected with the pathogenic bacterium Borrelia burgdorferi, the causative agent of Lyme Disease, and uninfected control animals. Despite ample statistical power to identify biologically relevant differences between infected and uninfected animals, we find no evidence for a global recombination rate response to bacterial infection. Moreover, broad-scale patterns of crossover distribution, including the number of achiasmate bivalents, are not affected by infection status. Although pathogen exposure can plastically increase recombination in some species, our findings suggest that recombination rates in house mice may be resilient to at least some forms of infection stress. This negative result motivates future experiments with alternative house mouse pathogens to evaluate the generality of this conclusion

Power to find differences in mean MLH1 focus count by the Mann-Whitney U-Test.

<p>Mock MLH1 datasets for infected and uninfected animals were simulated using parameter values derived from observed MLH1 data under the assumption that focus counts are normally distributed. Power was computed as the fraction of 1000 simulated datasets with a non-parametric Mann-Whitney U-test P-value <0.05.</p

Variation in meiotic and recombination sub-phenotypes across treatment groups.

<p>Variation in meiotic and recombination sub-phenotypes across treatment groups.</p

Representative image of a late pachytene spermatocyte stained with fluorescently labeled antibodies.

<p>SCP3, a component of the lateral elements of the synaptonemal complex, is stained in red. Sites of crossing over along the synaptonemal complex are denoted by green MLH1 foci. Centromeric proteins targeted by CREST antibodies are in blue. The white arrow points to the heterogametic sex chromosomes. Only MLH1 foci on autosomal bivalents were scored in this study (n = 23 for this image).</p

MLH1 foci counts in infected and control mice.

<p>MLH1 foci counts in infected and control mice.</p