Contrasting Range and Demographic Histories in two Palearctic Dragonfly Species (Odonata: Anisoptera)

Climatic suitability is often thought to provide insights into historical range changes, but its ability to predict effective population size has not been examined. In this study, two dragonflies from the Palearctic region, Somatochlora arctica and S. meridionalis, were examined to understand the relationship between their ecology and historical range.

S. arctica, a peatland specialist, and S. meridionalis, associated with shaded streams, were analyzed using different methods. These included demographic reconstructions using the pairwise sequentially Markovian coalescent (PSMC), maximum entropy (MaxEnt) species distribution models across six paleoclimatic intervals for about 3.3 million years, and ancestral state reconstructions of peatland specialization.

While S. arctica had a larger predicted suitable area, reaching its maximum extent during the Last Glacial Maximum, its inferred effective population size was smaller compared to S. meridionalis for most of the past 275,000 years. The analysis also showed that S. arctica's most probable gain of peatland specialization occurred in the Clade I lineage during the late Miocene, approximately 9.4 million years ago, which predates the modeling of climatic intervals.

This suggests a decoupling between climatic suitability and demographic history. Factors such as patchy breeding habitat, population structure, and the Scottish origin of the studied S. arctica may be contributing to this discrepancy. By integrating genomic, ecological, and phylogenetic data, this study provides a more comprehensive understanding of historical biogeography and highlights the need to consider the limitations of using suitable climate conditions as a proxy for available breeding habitat or relying solely on individual genomes to characterize species-wide demographic histories.