D3153: Incomplete barriers to heterospecific mating among Somatochlora species (Odonata: Corduliidae) as revealed in multi-gene phylogenies

Somatochlora, commonly known as the striped emeralds, is an enigmatic genus whose systematics have lagged other Odonata genera, with the last revision done by Walker (1925). Somatochlora males have elaborate claspers which are species-specific and provide a morphological barrier to heterospecific mating, but exceptions have been observed. The objective of this project was to investigate the occurrence of heterospecific mating between North American Somatochlora species as inferred from multi-gene phylogenies. We employed the use of two mitochondrial genes (COI and ND3) and two nuclear genes (EF1-α and ITS2) to construct well-substantiated phylogenies using a maximum parsimony optimality criterion. Compared to nuclear genes (nDNA), mitochondrial genes (mtDNA) mutate at an accelerated rate, thereby allowing for the genetic discrimination of populations and species. Monophyly of mtDNA lineages is expected for closely related species because ancestral mtDNA lineages go extinct after a speciation event four times faster than nDNA lineages. Observation of non-monophyletic mtDNA lineages but monophyletic nDNA lineages between Somatochlora sister-species would indicate mtDNA introgression and suggest heterospecific matings. Our results highlighted three instances of heterospecific mating in the following groups: 1) S. hineana + S. tenebrosa; 2) S. kennedyi + S. forcipata + S. franklini; 3) S. calverti + S. provocans + S. filosa. The recovered topology accurately reflected previous taxonomic understanding of the genus. These multi-gene phylogenies of North American Somatochlora are the first, providing a foundation for future ecological and evolution studies and knowledge for effective decision-making and public policy, which is especially important for endangered species, Somatochlora hineana.