From refugia to contact: pine processionary moth hybrid zone in a complex biogeographic setting

<p class="MsoCommentText">Contact zones occur at the crossroad between specific dispersal routes and are facilitated by biogeographic discontinuities. Here we focused on two Lepidoptera sister species that come in contact near the Turkish Straits System (TSS). We aimed to infer their phylogeographic histories in the Eastern Mediterranean and finely analyse their co-occurrence and hybridisation patterns in this biogeographical context.</p> <p class="MsoCommentText">We used molecular mitochondrial and nuclear markers to study 224 individuals from 42 localities. We used discordances between markers and complementary assignment methods to identify and map hybrids and parental individuals.</p> <p class="MsoCommentText">We confirmed the parapatric distribution of <i>Thaumetopoea</i><i> pityocampa </i>(Lepidoptera: Notodontidae) in the west and <i>T. wilkinsoni </i>in the east and identified a narrow contact zone. We identified several glacial refugia of <i>T. wilkinsoni</i> in southern Turkey with a strong east-west differentiation in this species. Unexpectedly, <i>T. pityocampa</i> crossed the TSS and occur in northern Aegean Turkey and some eastern Greek islands. We found robust evidence of introgression between the two species in a restricted zone in north-western Turkey, but we did not identify any F₁ individuals. The identified hybrid zone was mostly bimodal.</p> <p>The distributions and genetic patterns of the studied species were strongly influenced both by the Quaternary climatic oscillations and the complex geological history of the Aegean region. <i>Thaumetopoea pityocampa</i> and <i>T. wilkinsoni</i> survived the last glacial maximum in disjoint refugia and met in western Turkey at the edge of the recolonization routes. Expanding population of<i> T. wilkinsoni</i> constrained <i>T. pityocampa</i> to the western Turkish shore. Additionally, we found evidence of recurrent introgression by <i>T. wilkinsoni</i> males in several <i>T. pityocampa</i> populations. Our results suggest that some prezygotic isolation mechanisms, such as differences in timing of the adult emergences, might be a driver of the isolation between the sister species.</p>