Abstract
During the historical building of a species range, individual colonizers
have to confront different ecological challenges, and the capacity of
the species to broaden its range may depend on the total amount of
adaptive genetic variation supplied by evolution. We set out to increase
our understanding of what defines a range and the role of underlying
genetics by trying to predict an entire species’ range from the
geographical distribution of its genetic diversity under selection. We
sampled five populations of the western Mediterranean lizardPsammodromus algirus that inhabit a noticeable environmental
gradient of temperature and precipitation. We correlated the genotypes
of 95 individuals (18-20 individuals per population) for 21 SNPs
putatively under selection with environmental scores on a bioclimatic
gradient, using 1x1 km2 grid cells as sampling units.
By extrapolating the resulting model to all possible combinations of
alleles, we inferred all the geographic cells that were theoretically
suitable for a given amount of genetic variance under selection. The
inferred distribution range overlapped to a large extent with the
realized range of the species (77.46% of overlap), including an
accurate prediction of internal gaps and range borders. Our results
suggest an adaptability threshold determined by the amount of genetic
variation available that would be required to warrant adaptation beyond
a certain limit of environmental variation. These results support the
idea that the expansion of a species’ range can be ultimately linked to
the arising of new variants under selection.