Number of adapted genotypes per cell across the species’ range
Besides the general pattern by which fewer genotypes were adapted to
range boundaries than to core areas, we found two distinct scenarios
within the Iberian Peninsula (Fig. 6). On the one hand, in the northern
half of the peninsula there were many areas suitable for a high number
of genotypes. In such context, there is a high probability of finding
the few genotypes that are adapted to the challenging environmental
conditions characteristic of northern boundaries, which should
facilitate the establishment of the marginal populations that shape the
corresponding edge (Kawecki 2008; Hardie and Hutchings 2010; Halbritter
et al. 2015). Conversely, most of the southern half of Iberia seemed to
be suitable only for a small number of genotypes, despite the fact thatP. algirus is abundant in this area. However, several small areas
locally suitable for many genotypes were interspersed all across the
region. Such areas could therefore play an important role as sources of
specific genetic diversity adapted to the demanding, singular
environments that surround them (Holt and Keitt 2005; Sagarin et al.
2006). The genotyping of populations that inhabit demanding
environments, suitable for a small number of allele combinations, would
be crucial to sustain this assertion (Eckert et al. 2008; Gallet et al.
2018). Similarly, a model simulating the intensity of selection in both
sources and sinks of genetic diversity should be useful to test whether
the genetic variants adapted to demanding environments arise with higher
probability in source populations with more relaxed selection regimes
(Alleaume-Benharira et al. 2006).