Longitudinal range expansion and cryptic eastern species in the western Palaearctic oak gallwasp, <i>Andricus coriarius</i>

The oak gallwasp <i>Andricus coriarius</i> is distributed across the Western Palaearctic from Morocco to Iran. It belongs to a clade of host-alternating <i>Andricus</i> species that requires host oaks in two sections of <i>Quercus</i> subgenus <i>Quercus</i> to complete its lifecycle, a requirement that has restricted the historic distribution and dispersal of members of this clade. Here we present nuclear and mitochondrial sequence evidence from the entire geographic range of <i>A. coriarius</i> to investigate the genetic legacy of longitudinal range expansion. We show <i>A. coriarius</i> as currently understood to be para- or polyphyletic, with three evolutionarily independent (but partially sympatric) lineages that diverged c. 10 million years ago (mya). The similarities in gall structure that have justified recognition of single species to date thus represent either strong conservation of an ancestral state or striking convergence. All three lineages originated in areas to the east of Europe, underlining the significance of Turkey, Iran and the Levant as ‘cradles’ of gallwasp evolution. One of the three lineages gave rise to all European populations, and range expansion from a putative Eastern origin to the present distribution is predicted to have occurred around 1.6 mya.