Abstract
Understanding the drivers of heterogenous genomic divergence is
essential for uncovering the mechanisms that generate and constrain
biodiversity. The extent to which adaptation and speciation are
facilitated by reorganization of the recombination landscape remains
untested in many systems. Marine ecosystems, with their dynamic and
fluid habitats, offer a compelling context to investigate genomic
divergence. In this study we mapped genomic divergence and selection
across recombination landscapes of parapatric marine snail sister
species that we show have recently undergone secondary contact. Regions
of reduced recombination were enriched for genes exhibiting signatures
of negative selection, whereas regions of high recombination were
associated with genes under putative positive selection. Notably, the
recombination landscape of the population in parapatry of one species
(Scurria viridula) differs markedly from that of the other population
within this same species, highlighting the role of introgression in
reshaping recombination landscapes. In the other species (Scurria
zebrina), conservation of the recombination landscape and divergent
selection among populations suggest trapping of beneficial allele
combinations in regions of low recombination maintain the identity of
this species. Among species, signals of divergence with gene flow
consistently cluster within specific genomic regions characterized by
high recombination rate variation among the populations of S. viridula.
These results challenge theoretical expectations of recombination
evolution by showing that the causes of genomic divergence can be
population- specific. This study demonstrates that recombination
landscapes are key modulators of genomic divergence, with contemporary
evolutionary shifts that could enable populations to adapt to distinct
environments. Our findings provide new insights into the interplay
between recombination, selection, and gene flow during speciation,
underscoring the complexity of evolutionary trajectories in marine
systems.