Combining molecular datasets with strongly heterogeneous taxon coverage enlightens the peculiar biogeographic history of stoneflies (Insecta: Plecoptera)

Abstract

Extant members of the ancient insect order of stoneflies exhibit a disjunct, antitropical distribution, with one major lineage exclusively occurring in the Southern Hemisphere and the other, with few exceptions, on the Northern continents. Here, we address the biogeographic distribution and phylogenetic relationships of stoneflies using a phylogenetic workflow that combines both transcriptomic and Sanger sequence datasets with heterogeneous taxon coverage. We used a dataset comprising 2997 genes derived from the transcriptomes of 30 species and Sanger sequences of seven genes for 498 species. The backbone phylogeny was mainly inferred from the transcriptomic data, whereas the Sanger nucleotide sequence data provided high species density for divergence time estimation and diversification analyses. Our results show that the biogeographic pattern we observe today is primarily more likely shaped by long-distance over-land dispersal than by vicariance. We inferred that the ancestors of extant stoneflies originated in the Northern Hemisphere approximately 265 Ma and were presumably restricted to this area due to climatic and geographic boundaries. Our analyses suggest that with the break-up of Pangaea around 200 Ma and the associated climatic and geographical changes, two groups of stoneflies, the Anarctoperlaria and the Notonemouridae, dispersed to Gondwana and subsequently went extinct on the northern continents. Both groups likely dispersed across Gondwana before its break-up into the modern continents. At least one member of another group of ‘northern’ stoneflies, the Acroneuriinae, seems to have migrated from North America to South America around 67 Ma. We found four major net diversification rate shifts, indicating rapid radiation patterns that hampered a robust phylogenetic placement of these stonefly groups. Our study provides the first conclusive evolutionary explanation for the unique distribution pattern of stoneflies.