Cryptic species are organisms that include two or more independently evolving lineages that have been classified as a single nominal species because they are morphologically similar. Cryptic speciation has been related to the divergence of non-visual recognition systems (e. g. pheromones, acoustic signals). The American Rubyspot (Hetaerina americana) is a territorial damselfly species that has a wide distribution and can colonize a variety of habitats. It also shows variation in the morphology of the superior caudal appendages and, for this reason, several synonyms have been described. The population genetic structure has been previously described for a few populations where a high genetic differentiation was not related to the geographic distance between populations. To better understand phylogeographic and population genetic structure in this species, we genotyped 220 individuals of H. americana from 31 localities from Guatemala to the USA, using the mitochondrial gene COI, the nuclear region ITS1-5.8S-ITS2, and six nuclear microsatellites. We also analyzed the morphology of the caudal appendages of 101 males with geometric morphometric techniques to assess if morphological variation patterns are associated with genetic differentiation across populations.
Results/Conclusions
Mitochondrial DNA sequences revealed the presence of three haplogroups and strong phylogeographic structure. Nuclear data indicated two or three highly differentiated main genetic groups. The variation in the morphology of the caudal appendages showed two clearly distinguishable morphs that differed in the shape of the median lobe and the extension of the superior ridge and that was strongly congruent with the two nuclear genetic groups. On the other hand, mitochondrial DNA variation did not show congruence with the morphological and nuclear DNA differentiation pattern, what could be explained as a result of incomplete lineage sorting due to the probably recent divergence of the putative species or due to selection on the mitochondrial genome. Hetaerina americana has been treated as a single species, mainly because there is little differentiation among populations in ‘external’ characters (coloration pattern) along the whole distribution. Even though variation in the caudal appendages was previously recognized, this is the first time that this variation has been systematically analyzed. The results of our study suggest that a cryptic speciation process has occurred in H. americana and illustrate the complex evolutionary history of this damselfly group.