Population structure across genomic, environmental, and morphological axes in Synthemis eustalacta (Anisoptera: Synthemistidae)

The Great Dividing Range (GDR) is an expansive series of mountains, plateaus, and hills running parallel to the eastern coast of Australia, playing a pivotal role in shaping habitat expansion and contraction, as well as the persistence and speciation for a litany of taxa. Although genetic structuring along the GDR has been extensively studied in vertebrates, relatively few studies have focused on arthropods, and none have examined dragonflies despite their high species richness and endemism within Australia. Here, we investigate how the Great Dividing Range (GDR) has shaped genetic isolation in the Swamp Tigertail (Synthemis eustalacta) using an integrative approach that combines genomic data from target enrichment probes with ecological niche modeling (ENM), generating stacked prediction maps for each population. Metrics of genetic distance (Fst) indicate high levels of genetic isolation among populations, while admixture and ordination analyses reveal minimal geographic clustering. Correlation analyses indicate isolation by distance (IBD) as well as associations with climate variables, particularly those related to seasonal extremes in precipitation. However, we observe no correlations to elevation, proximity to rivers, competition, or niche overlap. Finally, morphological analyses of male genitalia reveal minimal variation among populations, providing insufficient evidence to justify the description of new species. We conclude that incipient speciation is underway within S. eustalacta, with mechanisms of isolation that are atypical compared to other taxa within the Great Dividing Range.