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Meiotic recombination is a central mechanism underlying sexual reproduction among eukaryotes. In many species, the recombination rate is strongly constrained by chromosome size, as the number of crossovers per chromosome generally ranges between one and no more than a few (around three to five). Yet, recombination rates are variable and can evolve between species, in particular when they differ in their reproductive system. According to theory, indirect selection towards higher recombination rates is expected to be stronger in inbred populations, such as selfing species compared with randomly mating species. To test for the impact of the mating system on the evolution of recombination rates, we leveraged a dataset with genetic maps, genome sizes, chromosome numbers, and life history traits in 200 seed plant species. After controlling for the chromosome size effect, the phylogeny, and map quality, we found a joint positive effect of the mating system and longevity on recombination rates, with higher recombination rates in mixed-mating and selfing species. We also found that mixed-mating and selfing species had a significantly higher number of crossovers in larger chromosomes than outcrossing species, suggesting selection for relaxed crossover interference in these former species. Our results point to the mating system as an important factor potentially shaping the evolution of recombination despite mechanical constraints acting on the number of crossovers per chromosome.
Brazier et al. (Mon,) studied this question.