Calopteryx splendens and relatives: taxonomy, biogeography, and phylogeny (Odonata: Calopterygidae)

We regard species, subspecies, and genera as measurable steps in an evolutionary process that requires time. Many species seem to require about one million years to become sufficiently distinct to be considered distinct. We test this in the damselfly genus Calopteryx Leach in Brewster, 1815, and especially in the group of Calopteryx splendens, trying to reconcile morphology with biogeography, including glaciations, and molecular phylogeny. We find that the C. splendens-group consists of four species, supported by distribution, morphology (wing patch size), COI, and ITS 1 and 2 (fragments of DNA), viz. C. exul Selys, 1853, C. samarcandica Bartenev, 1912, C. splendens (Harris, 1780), and C. xanthostoma (Charpentier, 1825). Only the first one fulfils the requirement of one million years in isolation, but all four seem to resist introgression. Despite enormous interpopulation variation, only two of the ca 25 named subspecies of C. splendens are considered valid: Calopteryx s. orientalis Selys, 1887, and C. s. syriaca Rambur, 1842. They began developing distinctive phenotypes during the Würm III deglaciation, ca 20 000 years ago, and have not yet reached species status. The taxonomic decisions made in this study include the placing of 17 named subspecies in synonymy with C. splendens splendens.

The last glacial maximum without doubt saw dramatic reductions in dragonfly populations that survived only in refugia. The Mediterranean basin was one of these, and central Asia another, more complex one. The western part of the basin, mainly Iberia, is home to C. xanthostoma, a species that recently became extinct in the Maghreb and is currently being outcompeted from south-western France to Liguria. There it meets C. splendens of various wing-patch morphs, coming from central Asia (Irano-Turania), via Anatolia, the Balkans, and Italy. To understand this, we assume two invasion waves occurred with different temperature preferences, causing them to disperse separately. The first one was cold-adapted, without a dark wing patch, and evolved in early preglacial times. It is still found along part of the southern margin of the Black Sea and probably evolved there. The second wave was warm-adapted with wide wing bands and androchrome females. It probably originated near the Zagros Mountains. All extant morphs can be explained as recent mixtures forming continuous clines of the two extremes.

Throughout the Holocene, the Zagros and the Black Sea populations recolonised central Asia and Siberia, eventually reuniting with those in the Baltic zone in the west, but this enormous territory needs much more study. In the south-east, Calopteryx did not cross the Pamir Mountain Knot. Calopteryx species that have been claimed to occur in the East Palaearctic mainly belong in Oriental genera such as Atrocalopteryx Dumont et al. 2005. The last common ancestor of American and Eurasian Calopteryx is believed to have lived in the Miocene age and migrated between continents via Beringia. It requires a genus name.