Reproductive isolation and intraspecific structure in Alpine populations of Erebia euryale (Esper, 1805) (Lepidoptera, Nymphalidae, Satyrinae)

Abstract

The subspecies of Erebia euryale (Esper, 1805) have been split into three groups based on morphology, differing in male genital characters. Two of them, the euryale group and the adyte group, are known to be strongly, but not completely, reproductively isolated. There is genetic evidence that their separation preceded the differentiation of subspecies within the euryale group. No such data exist on the third group, the recently recognized kunzi group. In this study, the degree of reproductive isolation between the kunzi group and the other two groups is assessed. In three secondary contact zones, a series of E. euryale populations were sampled in a transect perpendicular to the dividing line. Morphological characteristics showed a clinal gradient along each transect. The steepest gradient was found between the euryale and kunzi groups. Morphologically detectable introgression did not exceed two kilometres. This is comparable to the situation described earlier in contact zones of the euryale and adyte groups. In the contact area of the kunzi and adyte groups, the character gradient slope is more gradual and the morphologically detectable introgression zone is at least five times wider. In contrast to this, contact between subspecies belonging to the same group leads to virtually unrestricted morphological intermingling. It is concluded that the euryale group is reproductively more strongly isolated from the other two groups than the kunzi group is from the adyte group, and that subspecies belonging to the same group are interfertile to a high degree. It is argued that loss of genetic compatibility by long term separation is the main cause of the reproductive isolation between groups, and that, consequently, the actual intraspecific structure of E. euryale results from at least two, probably three, temporally separated differentiation events.