Molecular and taxonomic evidence unmasking hidden species diversity in the genus Acrobrycon (Characiformes: Characidae).

BRIÑOCCOLI, Y. F.; BOGAN, S.; ARCILA, D.; ROSSO, J. J.; MABRAGAÑA, E.; DELPIANI, S.; DÍAZ DE ASTARLOA, J. M; CARDOSO, Y. P.

Simposio; II Virtual Meeting of Systematics, Biogeography, and Evolution.; 2021

Patterns of fish diversity in the Neotropics are still poorly understood and mostlylimited to higher taxonomic levels (e.g., order or family level). Here, we conducteda review of the neotropical genus Acrobrycon distributed from the western AmazonBasin to the northwestern region of the La Plata Basin. A previous morphologicalstudy synonymized the two traditional recognized species in the genus, A. ipanquianus, distributed from the western portion of the Amazon River to the northwestregion of the La Plata River Basin, and A. tarijae, described from the Lipeo River inBolivia. We revisited in 24 individuals this result by collecting additional morphometric, meristic, and genetic data (COI mitochondrial gene), and three importantprocesses of geographic isolation in La Plata River Basin were collected. Our resultsrevealed a more complex history of diversification and geographic distribution acrossAcrobrycon species than previously suspected. We present new evidence that leadsus to reconsider the validity of A. tarijae formerly synonymous of A. ipanquianus,which are distinguished by the number of vertebrae (37-39 vs. 41-42), pleural ribs(12-13 vs 14), and unbranched rays (v-vi vs. ii-iii) in the anal fin, respectively. Ourgenetic result, indicated two major genetic clusters of A. tarijae: the first groupconsisted of specimens from the Bermejo, Pilcomayo, Itiyuro and Juramento RiverBasins (northern Argentina), and the second group is composed of specimens fromthe southernmost basins, such as the Sal´ı River in Tucum´an and the Quinto Riverin the province of San Luis separating these groups at the genetic level by 1.87%.This result suggests that the genetic structure may be a consequence of the geographical distance that separates the two groups and the type of basin. Our resultsalso provided evidence of a range expansion of A. tarijae to the Quinto River, thisbeing the only record known for this province and the southernmost known for thisspecies.