Timing and direction of faunal exchange between the Nearctic and the Palaearctic in Odonata

Aim

Species have different distribution patterns across the globe and among biogeographical regions. The Nearctic and Palaearctic regions share lineages because of their parallel biogeographic histories and ecological conditions. As the number of phylogenetic studies increases, there are more insights into past exchange events between these two regions and their effects on the current distribution of diversity. However, several groups have not been tested and an overall generalization is still missing. Here, we analyse the biogeographic history across multiple genera of odonates to elucidate a general process of species exchange, vicariance and species divergence between these two regions.

Location

The Holarctic, including the entire Nearctic and the East and West Palaearctic.

Taxon

14 genera of Odonata (Insecta).

Methods

We reconstructed a time-calibrated phylogenetic tree for each genus to determine species relationships and divergence time using 3614 COI sequences of 259 species. Biogeographic ancestral range estimation was inferred for each phylogeny using BioGeoBEARS. Preferred habitat (lotic versus lentic) was established for each species.

Results

Exchange events were not restricted in time, direction or either lentic habitat or lotic habitat. Most genera crossed between both regions only once, and it was mainly across the Beringia, while three diverse anisopteran genera revealed multiple exchanges. Recent exchanges during the Pleistocene were associated with cold-dwelling and lentic species.

Main Conclusions

Our finding reveals the absence of a generalizable pattern of species exchange and divergence between the Nearctic and Palaearctic regions; instead, we found lineage-specific biogeographic patterns. This finding highlights the complexity of drivers and functional traits that shaped current diversity patterns. Moreover, it emphasizes that general conclusions cannot be formulated based on one single clade.