Historical recombination maps diverge between Eurasian blackcap populations with distinct migratory strategies

Recombination generates new combination of alleles, whereby it maintains haplotype diversity and enhances the efficacy of selection. Despite the apparent stasis in positioning recombination events in birds, recombination rates differ widely across the genome and within species. The causes of recombination rate variation and its evolutionary impact on natural populations remain poorly understood. We used whole-genome resequencing data of 167 individuals of the Eurasian blackcap (Sylvia atricapilla) to characterise the historical recombination landscape variation at broad and fine scales among populations with distinct migratory phenotypes. We additionally evaluated the interplay between recombination rates with patterns of genetic diversity, population divergence (based on Fst and dxy), and potential signs of selection. Our comparative analyses revealed: i) Lower divergence of recombination maps at the broad scale and higher variability at fine scales. Resident island populations showed higher variability in recombination patterns among them and with continental populations. Recombination rates were more conserved in continental populations regardless of the migratory phenotype. ii) The degree of divergence between recombination maps correlated with population differentiation. It could also recapitulate population-specific demographic history and genetic structure. iii) Recombination rates correlated negatively with Fst and positively with nucleotide diversity and dxy, suggesting that recombination may reduce the effect of linked selection over the loss of neutral diversity. We identified chromosomal regions with potential signs of linked selection. This study evidences that recombination is a variable trait that shapes the diversity and evolution of population differentiation in the blackcap.