Integrative cytogenetic and molecular evidence reveals a new cryptic lineage within the “Parodon suborbitalis complex” (Characiformes: Parodontidae)

Parodontidae is a Neotropical fish family arranged in Saccodon, Parodon, and Apareiodon genera. Despite morphological similarities in some paired species, genetic and chromosomal markers have been useful for resolving taxonomic uncertainty in Parodontidae. Parodon representatives inhabiting the Amazonian basin are among the species with subtle morphological features that require accurate identification. Therefore, this study compared Parodon species using cytogenetic and genetic markers, with the aim of molecular species delimitation. Additionally, two Parodon populations from the Amazon River basin, morphologically identified as Parodon sp. (Peixe River) and Parodon cf. buckleyi (Branco River), were cytogenetically and molecularly characterized. Both Parodon sp. and P. cf. buckleyi presented a 2n = 54 and chromosome markers similar to those of Parodon nasus, but with species-specific differences. Genetic distance, Bayesian analysis, and molecular species delimitation methods recognized P. guyanensis, P. pongoensis, P. hilarii, P. caliensis, P. suborbitalis, P. magdalenensis, P. apolinari, P. nasus, P. cf. buckleyi,and Parodon sp. as valid species. Integrative cytogenetic and molecular data analysis points to Parodon sp. (Peixe River) as a Molecular Operational Taxonomic Unit in Parodontidae. These results reveal hidden diversity within Parodon and suggest that the “P. suborbitalis complex” is non-monophyletic, with distinct groups arranged within a biogeographic framework.