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

Kahraman İpekdal,Laure Sauné,Carole Kerdelhué,Christian Burban,Andrea Battisti

doi:10.1002/ece3.6018

Abstract

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 analyze their co‐occurrence and hybridization patterns in this biogeographic context.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.We confirmed the parapatric distribution of Thaumetopoea pityocampa (Lepidoptera: Notodontidae) in the west and Thaumetopoea wilkinsoni in the east and identified a narrow contact zone. We identified several glacial refugia of T. wilkinsoni in southern Turkey with a strong east–west differentiation in this species. Unexpectedly, T. pityocampa 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 northwestern Turkey, but we did not identify any F1 individuals. The identified hybrid zone was mostly bimodal.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. T. pityocampa and T. wilkinsoni survived the last glacial maximum in disjoint refugia and met in western Turkey at the edge of the recolonization routes. Expanding population of T. wilkinsoni constrained T. pityocampa to the western Turkish shore. Additionally, we found evidence of recurrent introgression by T. wilkinsoni males in several T. pityocampa 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.

Highlights

Climate and habitat changes can facilitate range movements, which can cause secondary contacts between species or lineages (Taylor, Larson, & Harrison, 2015)
Our results allow to go far beyond previous knowledge about the evolution of the pine processionary moth (PPM) sister species. They suggest that the two species diverged in allopatry, survived the successive glacial maxima in disjoint refugial areas, and met at the extreme edge of their recolonization routes during the last interglacial
Even if reproductive isolation probably due to premating barriers is found, hybridization seems to have played a major role in species displacement, in favor of T. wilkinsoni that constrained T. pityocampa to western Anatolia

Summary

Introduction

Climate and habitat changes can facilitate range movements, which can cause secondary contacts between species or lineages (Taylor, Larson, & Harrison, 2015). The Quaternary glacial cycles have strongly influenced the current distributions of Mediterranean species and their genetic diversity (Hewitt, 1999; Schmitt, 2007). Every 100,000 years and forced species to contract their ranges into restricted refugia, while interglacial periods allowed them to expand northward (the Expansion-Contraction model) (Taberlet, Fumagalli, Wust-Saucy, & Cosson, 1998). In regions strongly affected by glaciations, most of the genetic diversity has accumulated in lower latitudes (Petit et al, 2003), while northern populations show decreased allelic richness and signs of demographic expansions, a pattern known as “southern richness and northern purity” (Hewitt, 1999). The glacial cycles have affected sea levels and land configurations, thereby modifying landmass connectivity, and possible dispersal routes, over time (Hewitt, 2011). The genetic footprints of species' responses to these successions of climate changes have been extensively studied for many species in Europe and North America, while studies in the Near East remain scarce

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