Parallel use of a shared genomic island of speciation in clinal and mosaic hybrid zones between cryptic seahorse lineages (original) (raw)

Diverging semi-isolated lineages either meet in narrow clinal hybrid zones, or have a mosaic distribution associated with environmental variation. Intrinsic reproductive isolation is often emphasized in the former and local adaptation in the latter, although both can contribute to isolation. Rarely these two patterns of spatial distribution are reported in the same study system, while this could provide fundamental information on the endless debate about the relative contribution of intrinsic reproductive isolation and local adaptation on the speciation process. Here we report that the low diversity long-snouted seahorse Hippocampus guttulatus is genetically subdivided into five cryptic semi-isolated lineages. Along the Atlantic coasts, northern and southern lineages meet and coexist with little hybridization in the southwest of France, forming a clinal hybrid zone. In the Mediterranean Sea, two lineages have a mosaic distribution associated with lagoon-like and marine habitats. A f...