Comparative phylogeography uncovers evolutionary past of Holarctic dragonflies

Abstract

Here, we investigate the evolutionary history of five northern dragonfly species to evaluate what role the last glaciation period may have played in their current distributions. We look at the population structure and estimate divergence times for populations of the following species: Aeshna juncea (Linnaeus), Aeshna subarctica Walker, Sympetrum danae (Sulzer), Libellula quadrimaculata Linnaeus and Somatochlora sahlbergi Trybom across their Holarctic range. Our results suggest a common phylogeographic pattern across all species except for S. sahlbergi. First, we find that North American and European populations are genetically distinct and have perhaps been separated for more than 400,000 years. Second, our data suggests that, based on genetics, populations from the Greater Beringian region (Beringia, Japan and China) have haplotypes that cluster with North America or Europe depending on the species rather than having a shared geographic affinity. This is perhaps a result of fluctuating sea levels and ice sheet coverage during the Quaternary period that influenced dispersal routes and refugia. Indeed, glacial Beringia may have been as much a transit zone as a refugia for dragonflies. Somatochlora sahlbergi shows no genetic variation across its range and therefore does not share the geographic patterns found in the other circumboreal dragonflies studied here. Lastly, we discuss the taxonomic status of Sympetrum danae, which our results indicate is a species complex comprising two species, one found in Eurasia through Beringia, and the other in North America east and south of Beringia. Through this study we present a shared history among different species from different families of dragonflies, which are influenced by the climatic fluctuations of the past.

Keywords: Aeshna; Beringia; Circumboreal; Dragonflies; Holarctic; Libellula; Phylogeography; Somatochlora; Sympetrum.

Figure 1. Haplotype networks for the five dragonfly species.

(A) A. juncea, (B) A. subartica, (C) L. quadrimaculata, (D) S.danae, and (E) S. sahlbergi. Each circle represents a unique haplotye and the size of the circle is proportional to the number of the samples that share that haplotype. Haplotypes are connected to each other by lines and the ticks on the connecting lines indiacate number of nucleotide changes between the haplotypes. Each haplotype (circle) is colored according the geographic affinity of the samples within it. All the haplotypes within each network are numbered. Two very divergent groups were recovered in S. danae. Group A is highlighted in gray color while Group B is highlighted in yellow color.

Figure 2. Predicted population cluster and DAPC analyses.

For all species we show the Linear Discriminant scatterplot on the left and the membership probability plots on the right. (A) Aeshna juncea, (B) Aeshna subartica, (C) Libellula quadrimaculata and (D) Sympetrum danae-group B. All the linear discriminant plots show separation of the populations along Linear Discriminant axis 1 (LD1) and 2 (LD2), except for S. danae, since there are only two populations that are separated only on LD1. In the membership probability plot all individuals are colored according to their geographical origin.

Figure 3. Chronograms showing the divergence time estimates for the four Holarctic dragonflies.

Mean estimated ages for the nodes are indicated in bold. Major clades are highlighted in accordance with predicted population clusters as shown in Fig. 2. Each sample within a population is colored according to its geographic affinity.