3.2 Reproductive isolation
In both hybrid regions, i.e., north-central and north-western Spain, we detected strong and asymmetric mechanical reproductive isolation. In north-central Spain, mechanical and tactile barriers between I. elegans males and I. graellsii females impeded 65% of the matings, while between I. graellsii males and I. elegans females 76% of matings were impeded. When those barriers were estimated in I. elegansbackcrosses, i.e., between I. elegans males and hybrid females, barriers impeded 33% of the matings, while between hybrid males andI. elegans females, barriers impeded 75% of matings. More isolation was detected in I. graellsii backcrosses, betweenI. graellsii males with hybrid females 100% of the copulations were prevented, but we find no isolation between hybrid males andI. graellsii females (0%) (Figure 2A). The strength of mechanical and tactile barriers in heterospecific crosses and I. elegans and I. graellsii backcrosses in north-western Spain are given in Figure 2B [data from (Arce-Valdés, Ballén-Guapacha, Chávez-Rios, & Sánchez-Guillén, under review; Sánchez-Guillén et al., 2012)].