Darwin Returns to the Galapagos: Genetic and Morphological Analyses Confirm the Presence of Tramea darwini at the Archipelago (Odonata, Libellulidae).

Abstract

Simple SummaryFlying insects are able to colonize oceanic islands by both active and passive dispersal. Ten species of dragonflies are found in the Galapagos archipelago, located at 900 km from mainland South America. Shortly after the publication of Darwin’s “The Origin of Species”, one of the dragonflies from these islands was named after him as Tramea darwini. However, subsequent studies considered it to belong to another continental species of the same genus known as Tramea cophysa. Here, we studied a series of specimens of Tramea collected in 2018 from the Islands of San Cristobal, Isabela, and Santa Cruz, with the aim of determining their specific identity, through a combination of molecular and morphological analyses. Our results indicate that the Galapagos specimens examined belong to Tramea calverti, another continental species, and not to T. cophysa as previously thought. Following the principle of priority in taxonomic nomenclature, Tramea calverti, which was described in 1910 by Muttkowski, should hereafter be considered a synonym of Tramea darwini, which was described in 1889 by Kirby; hence, the species named after Darwin is to be considered valid, inhabiting both the Galapagos islands and continental America.The status of the Tramea species present in the Galapagos Islands (Odonata, Libellulidae) has been the subject of a long-standing debate among odonatologists. Here, we use molecular and morphological data to analyze a series of specimens from this genus collected in 2018 from the Islands of San Cristobal, Isabela, and Santa Cruz, with the aim of determining their relationship with Tramea calverti Muttkowski and with their currently considered senior synonym T. cophysa Hagen. We combined sequencing of mitochondrial and nuclear DNA with morphological examination of several specimens of Tramea, including representatives of continental T. cophysa and T. calverti. Our molecular analyses place the Tramea from Galapagos in the same clade as T. calverti, with T. cophysa as a closely related species. The morphological analyses found only one consistent difference between T. cophysa and T. calverti: the presence of an accessory lobe in the male vesica spermalis of T. cophysa that is absent in T. calverti and in the Tramea from Galapagos. In agreement with our genetic results, the overall morphological differences documented by us indicate that the Galapagos material examined is conspecific with T. calverti. In light of this, and following the principle of priority in taxonomic nomenclature, Tramea calverti Muttkowski, 1910 should hereafter be considered a junior synonym of Tramea darwini Kirby, 1889.