Integrated analysis reveals a new species of Corydoras Lacepede, 1803 (Siluriformes: Callichthyidae) in the lower Iguassu River, Brazil

Corydoras is the richest genus of Corydoradinae, and many of its species have not been identified to date. We characterized Corydoras carlae and Corydoras sp. by performing cytogenetic, morphometric, and molecular analyses to facilitate correct identification and species delimitation and contribute an understanding of the evolutionary process of this group of fish. Individuals of C. carlae were collected in the Florido River, a tributary of the Iguassu River upstream of Iguassu Falls, and individuals of Corydoras sp. were collected in the Poco Preto River, a tributary of the Iguassu River downstream of Iguassu Falls. Corydoras sp. presented an extra rDNA 5S marker in an interstitial position on the short arm of one of the chromosomes of the submetacentric pair 15. Mitochondrial (COI) and nuclear (RAG1) sequences were efficient in discriminating C. carlae and Corydoras sp. Both species had exclusive haplotypes, which suggests the absence of gene flow between species. Furthermore, species delimitation analysis (GMYC and ABGD) suggested two MOTUs for Corydoras specimens from the Iguassu River. Differences in morphometric proportions were also observed. Considering the data gathered in this study, C. carlae and Corydoras sp. comprise distinct evolutionary lineages that are probably undergoing a recent speciation process.

Automated summary

This study characterized Corydoras carlae and Corydoras sp. through cytogenetic, morphometric, and molecular analyses, revealing distinct evolutionary lineages and a recent speciation process. Mitochondrial and nuclear sequences were effective in discriminating between the two species, suggesting the absence of gene flow between them. The study also identified differences in morphometric proportions and suggested two Molecular Operational Taxonomic Units (MOTUs) for Corydoras specimens from the Iguassu River.