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

Abstract

Mating between species occurs within many insect orders. The result of heterospecific mating depends upon the effectiveness of pre- and post-reproductive barriers. Incomplete reproductive barriers lead to introgression of DNA into one species or both. Intricate genital morphology among dragonflies provides little assurance of species specificity given that heterospecific mating or mating attempts have been observed among many species. The genetic consequence is unknown for many heterospecific matings. For example, Somatochlora species mating and genetic exchange have been hypothesized based on observational records and individuals with hybrid morphology. We investigate the potential of heterospecific mating between North American Somatochlora species as inferred from multi-gene phylogenies. We used mitochondrial genes (COI and ND3) and nuclear genes (EF1-α and ITS2) to construct phylogenies using maximum parsimony. 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 non-monophyly of mtDNA clades in the following groups: (i) S. hineana + S. tenebrosa; (ii) S. kennedyi + S. forcipata + S. franklini; and (iii) S. calverti + S. provocans + S. filosa. Analysis of partitioned Bremer support indicates that mtDNA COI largely contributed to the non-monophyly of these species, thus suggesting mtDNA introgression resulting from heterospecific matings. Additionally, the topology resulting from the combined data analysis was concordant with previous taxonomic understanding of Somatochlora species groups. 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 the endangered species, S. hineana.