Multiple old differentiation centres around the Alps and complex range expansion patterns in a semi-aquatic insect: the phylogeny and biogeography of the Wormaldia occipitalis species complex (Trichoptera)

The understanding of cryptic species complexes with their often highly interesting biogeographical patterns is still a crucial aspect in evolutionary biology and related disciplines. Trichoptera are a group of insects particularly rich in unresolved groups. One example is the Wormaldia occipitalis species complex in which morphological studies suggest remarkable patterns of differentiation. In order to determine genetic differentiation and phylogenetic structure, one mitochondrial (COI) and two nuclear markers (CAD, wingless) were analysed for the W. occipitalis species complex around the Alps and northwards to Germany. The morphology-defined differentiation pattern was also observed at the genetic level. The morphologically well distinguishable groups W. occipitalis and W. subterranea were identified as two genetically distant monophyletic groups with about 10 % genetic divergence of the mitochondrial marker. These two taxa likely split during the Mio-Pliocene transition. Genetic analyses revealed four subgroups within W. occipitalis and three within W. subterranea . Several possible postglacial dispersal and differentiation processes are proposed. Thereby, W. occipitalis from the western Alps and individuals of W. subterranea from the eastern Alps spread towards Central Europe after the Last Glacial Maximum. Today, both species groups are sympatric and partly syntopic in the recolonised area in western Germany but apparently allopatric in their centres of origin around the Alps. The high genetic differentiation, lack of detectable genetic evidence for hybridisation, their syntopic distribution and the morphological distinctness indicate that W. occipitalis and W. subterranea are two distinct species. The genetically determined subgroups might represent subspecies.