Evolution of Mayflies (Ephemeroptera) Across the Palearctic Mountains: The Biogeographical Links Between the Caucasus and Adjacent Ranges, Central Asia and the Himalayas

ABSTRACT The biodiversity of the highest Palearctic mountains is extraordinary, yet its evolution and biogeographic links from a global perspective remain poorly understood. This study focuses on the diversification and biogeography of mayflies (Ephemeroptera) distributed across several prominent mountain ranges, including the Caucasus and adjacent Mediterranean and Irano‐Anatolian ranges, the mountains of Central Asia (Tian Shan and Pamir) and the Himalayas. Using molecular phylogenetic tools applied to our model group Epeorus ( Caucasiron ), we test whether the most species‐rich area, the Caucasus, provided lineages for the Central Asian and Himalayan mayfly diversity. The results showed that Caucasian and Asian E . ( Caucasiron ) taxa are distinct monophyletic clades that diverged from a widely distributed ancestor in the Middle Miocene. Both clades diversified in situ during the Late Miocene and Pliocene orogeny, with no evidence of dispersal between them. The mayflies of the subgenus E . ( Caucasiron ) likely originated in Asia and dispersed to the Irano‐Anatolian region and the Caucasus, where they subsequently diversified. This dispersion likely occurred due to the regression of the Paratethys Sea, and the early formation of mountains with suitable climatic conditions that linked Central Asia with the Caucasus before the Late Miocene/Pliocene period of intensive aridification. Our study emphasises that historical migration, along with the complex orogenic and climatic history, rather than dispersal from the biodiversity centre, plays a pivotal role in the evolution and biogeography of the Caucasian–Himalayan mountain mayflies. Additionally, a new Asian subgenus, Protoiron subgen. n., was established based on molecular phylogeny and morphology.