Historical Areas of Hybridization in Two Striped Emerald Dragonfly Species

The Hine's Emerald (Somatochlora hineana) is a federally endangered North American dragonfly, which has experienced significant declines due to anthropogenic forces including human encroachment into its sensitive spring fed wetland habitat and climate change. Previous research indicates hybridization with its ecologically generalist and widespread conspecific, the Clamp-Tipped Emerald (Somatochlora tenebrosa), which may induce hybridization-mediated extinction or genetic swamping. The aim of this paper is to investigate the patterns of hybridization between S. hineana and S. tenebrosa by inferring historical species ranges using Paleoecological niche modeling (PaleoENM), examining genetic structure using haplotype networks, and determining gene flow with introgression tests, shedding light on how, why, when, or where hybridization occurs in these species. Our results reveal evidence of hybridization occurring between S. hineana and S. tenebrosa among populations in Benzie County, Michigan and a newly discovered hybrid individual in Oregon County, Missouri. PaleoENM models show patterns of contact and separation across the Pleistocene, highlighting potential hybridization events throughout periods of glaciation. Finally, Introgression tests reveal evidence for unidirectional hybridization, which may result in genetic swamping of the endangered Hine's Emerald. Such studies provide essential genetic context for conserving ecologically sensitive and endangered species, identifying conservation priorities, and determining whether hybridization and introgression pose additional threats to the long-term genetic integrity and persistence of endangered populations.