Demographic modelling helps tracking the rapid and recent divergence of a conifer species pair from central Mexico

Secondary contact of recently diverged species may have several outcomes, ranging from rampant hybridization to reinforced reproductive isolation. In plants, selfing tolerance and disjunct reproductive phenology may lead to reproductive isolation at contact zones. However, they can evolve under both allopatric or parapatric frameworks and originate from adaptive and/or neutral forces. Inferring the historical demography of diverging taxa is thus a crucial step to identify those factors that may lead to putative reproductive isolation. We explored various competing hypotheses to account for the rapid divergence of a fir species complex (Abies flinckii - A. religiosa) distributed in ‘sky-islands’ across central Mexico (i.e., along the Trans-Mexican Volcanic Belt; TMVB). Despite co-occurring in two independent sympatric regions (west and center), these taxa rarely interbreed because of disjunct reproductive phenologies. We genotyped 1,147 SNPs, generated by GBS, across 23 populations, and ...