Usually, adaptive phenotypic differentiation is paralleled by genetic
divergence between locally adapted populations. However, adaptation can
also happen in a scenario of non-significant genetic divergence due to
intense gene flow and/or recent differentiation. While this phenomenon
is rarely published, findings on incipient ecologically-driven
divergence or isolation by adaptation are relatively common, which could
confound our understanding about the frequency at which they actually
occur in nature. Here, we explore genome-wide traces of divergence
between two populations of the lacertid lizard Psammodromus algirus
separated by a 600 m elevational gradient. These populations seem to be
differentially adapted to their environments despite showing low levels
of genetic differentiation (according to previously studies of mtDNA and
microsatellite data). We performed a search for outliers (i.e. loci
subject to selection) trying to identify specific loci with FST
statistics significantly higher than those expected on the basis of
overall, genome-wide estimates of genetic divergence. We find that local
phenotypic adaptation (in terms of a wide diversity of characters) was
not accompanied by genome-wide differentiation, even when we maximized
the chances of unveiling such differentiation at particular loci with
FST-based outlier detection tests. Instead, our analyses confirmed the
lack of differentiation on the basis of more than 70,000 SNPs, which is
concordant with a scenario of local adaptation without any degree of
isolation by environment. Our results add evidence to previous studies
in which local adaptation does not lead to any kind of isolation (or
early stages of ecological speciation), but maintains phenotypic
divergence despite the lack of a differentiated genomic background.
Low genome‐wide divergence between two lizard populations with high adaptive phenotypic differentiation