Remarkable genetic homogeneity supports a single widespread species of Hoplosternum littorale (Siluriformes, Callichthyidae) in South America

Hoplosternum littorale is a widespread, non-migratory, air-breathing armored catfish (Callichthyidae, Siluriformes) present in most river drainages of tropical South America. This species has invaded aquatic habitats out of its native range. The distribution and unity of this species is supported by strong morphological evidences, but only few molecular data are available. As for February 2017, 45 partial mitochondrial gene sequences for H. littorale were deposited at the U.S. National Center for Biotechnology Information (NCBI) GenBank. The nearly complete mitochondrial genomes from two individuals of H. littorale sampled in geographically isolated populations were sequenced and compared to the intraspecific divergence encountered in a related species, Corydoras nattereri. Tamura-Nei corrected distances between the mitochondrial genomes from the two H. littorale was 0.004, equivalent to the distance found among individuals from the same population of C. nattereri (0.002) and considerably smaller than the distance between C. nattereri and C. schwartzi (0.123). An insertion of 30 nucleotides between the ATPase 6 and the COIII genes was identified in H. littorale. This insertion is homologous to the one previously noted in two species of Corydoras. This work supports H. littorale as a single and widespread species of Callichthyidae catfish. The new genetic resources for H. littorale are now available to support further studies with larger sampling sizes.