Description of two threatened and polymorphic seasonal killifish species of the genus Hypsolebias (Cyprinodontiformes: Rivulidae) from the Piranhas-Açu River basin, in the Brazilian semiarid

Abstract In this study we used integrative taxonomy approach to describe two new species of the Hypsolebias antenori species group found in the lower Piranhas-Açu River basin in Rio Grande do Norte State, northeastern Brazil. The new species differs from the other congeners primarily by a combination of morphological traits: color patterns of males and females, position of the dorsal-fin origin, number of filaments on anal and dorsal fins, number of scale series and cephalic neuromasts. Using sequences of the mitochondrial cytochrome c oxidase subunit I (cox1) gene, we reconstructed the phylogenetic relationships of the HAG through Bayesian inference with a molecular clock analysis. Our results suggest that the diversification events of the group occurred between the middle and end of the Pleistocene, a period marked by significant diversification among Caatinga’s seasonal rivulids. We also identified color polymorphism in H. guararug, new species, and H. negobispoi, new species, and discussed its potential relationship with oil exploration activities in the region. Finally, we discuss the environmental impacts in the area of occurrence of the new species, suggesting the Endangered (EN) and Critically Endangered status (CR), respectively, based on IUCN criteria, as well as recommendations for their conservation in the semiarid temporary pools.