Peer Review #2 of "Unusually low genetic divergence at COI barcode locus between two species of intertidal Thalassaphorura (Collembola: Onychiuridae) (v0.2)"

Abstract

Species classification is challenging when the taxa display limited morphological differences. In this paper, we combined morphology and DNA barcode data to investigate the complicated taxonomy of two Onychiurid Collembolan species. Thalassaphorura thalassophila and T. debilis are among the most common arthropod species in intertidal ecosystems and are often considered to be synonymous. Based on morphological and barcode analyses of fresh material collected in their type localities, we show that each of them is the state of the species. However, their morphological distinctiveness was only supported by a molecular divergence much smaller than previously reported at the interspecific level among Collembola. This divergence was even smaller than interpopulation divergences recognized in the related edaphic species T. zschokkei, as well as those known between MOTUs within many Collembolan species. Our results may indicate a link between low genetic interspecific divergence and intertidal habitat, as the only biological peculiarity of the two species of interest compared to other Collembolan species analyzed to date is their strict intertidal life.