Species limits and introgression in Pimelodus from the Magdalena-Cauca River basin.

Low morphological differentiation among taxa hampers their appropriate identification, basic biological studies and promotion of any conservation effort. Aiming to provide the first insight into the evolution and speciation among north-western South American members of Pimelodus, this study tested the hypothesis that Pimelodus yuma, Pimelodus grosskopfii and Pimelodus crypticus represent three independently evolving species and explored signals of interspecific hybridisation. The outcomes based on mitochondrial (cox1) and nuclear (RADseq, microsatellites and rag2) markers combined with coalescence-based and allele-frequency methods confirmed that each studied species represents an independently evolving unit. Contrary to expectations, P. yuma was found as a sister clade of P. blochii, while P. crypticus (formerly confused with P. blochii) was phylogenetically closer to P. grosskopfii. We also found strong evidence of ancient introgression (0.66-3.32 mya) between the non-sibling species P. yuma and P. grosskopfii, breaking the absence of interbreeding and the independent evolutionary trajectory among north-western South American Pimelodus during their diversification history, a pre-requisite to define species limits. However, there were non-significant values of current gene flow between them, supporting the hypothesis of full isolation.

Population genetics of the endangered catfish Pseudoplatystoma magdaleniatum (Siluriformes: Pimelodidae) based on species-specific microsatellite loci

The Neotropical catfish genus Pseudoplatystoma comprises eight species of large size, widely distributed in South American basins. The endangered species P. magdaleniatum is endemic to Magdalena basin (Colombia), experiences high fishing pressure and its population genetics is relatively unknown. To study the genetic status and structure of P. magdaleniatum, 25 species-specific polymorphic microsatellite loci were developed using next-generation sequencing and then tested in samples collected in the Magdalena-Cauca basin. Based on 15 of these loci, P. magdaleniatum showed a high number of alleles per locus (9-10), high values of observed (0.762-0.798) and expected (0.770-0.791) heterozygosities, recent reduction of population size and gene flow. These findings constitute a baseline to measure potential changes in genetic diversity and structure of this commercially important species in a basin undergoing high anthropogenic activities.(AU)

El género de bagres neotropicales Pseudoplatystoma comprende ocho especies de gran tamaño, ampliamente distribuidas en las cuencas de Suramérica. La especie en peligro de extinción P. magdaleniatum es endémica de la Cuenca del Magdalena (Colombia), experimenta una alta presión pesquera y su genética poblacional es relativamente desconocida. Para estudiar el estado y estructura genética de P. magdaleniatum, se desarrollaron 25 loci microsatélites polimórficos especie específicos utilizando secuenciación de próxima generación y se evaluaron en muestras recolectadas en la Cuenca del Magdalena-Cauca. Con base en 15 loci, P. magdaleniatum mostró un alto número de alelos por locus (9-10), valores altos de heterocigosidad observada (0.762-0.798) y esperada (0.770-0.791), reducción reciente del tamaño poblacional y flujo génico. Estos hallazgos constituyen una línea de base para medir cambios potenciales en la diversidad y estructura genética de esta especie comercialmente importante en una cuenca sometida a altas actividades antropogénicas.(AU)

Development of microsatellite loci and population genetics in the bumblebee catfish species Pseudopimelodus atricaudus and Pseudopimelodus magnus (Siluriformes: Pseudopimelodidae)

The Neotropical freshwater catfish Pseudopimelodus atricaudus and Pseudopimelodus magnus are two recently discovered species endemic to the Colombian Magdalena-Cauca River basin. In this study, a set of 13 microsatellite loci were developed by using next generation sequence technology to assess the genetic diversity and population structure in P. atricaudus and test for cross-species amplification in P. magnus. Both species exhibited high genetic diversity (P. atricaudus: Na: 9.000 - 9.769 alleles/locus, Ho: 0.760 - 0.804, HE: 0.804 - 0.840; P. magnus: Na: 12.8 - 5.4 alleles/locus, Ho: 0.638 - 0.683, HE: 0.747 - 0.755) compared to the mean levels of genetic diversity reported for Neotropical Siluriformes, and lack of genetic differentiation among sampling sites within the Cauca River (P. atricaudus: F'ST=0.013 - 0.017, P > 0.05, D'est= -0.004 - 0.023, P > 0.05; P. magnus: F'ST= 0.031, P= 0.055; D'est= 0.045, P= 0.058). This work is the first insight on the diversity and the population genetics of species of the family Pseudopimelodidae and provides a framework to further population genetic and conservation analyses needed in this poorly studied family at the microevolutionary level.(AU)

Los bagres neotropicales Pseudopimelodus atricaudus y Pseudopimelodus magnus son dos especies recientemente descubiertas, endémicas de la cuenca Magdalena-Cauca en Colombia. En este estudio, se desarrollaron 13 loci microsatélites usando tecnología de secuenciación de próxima generación para evaluar la diversidad genética y la estructura poblacional de P. atricaudus y evaluar su amplificación cruzada en P. magnus. Ambas especies exhibieron altos valores de diversidad genética (P. atricaudus: Na: 9.000 - 9.769 alelos/locus, HO: 0.760 - 0.804, HE: 0.804 - 0.840; P. magnus: Na: 12.8 - 5.4 alelos/locus, HO: 0.638 - 0.683, HE: 0.747 - 0.755) comparados con los valores promedios de diversidad genética reportados para Siluriformes neotropicales, y ausencia de estructura genética entre los sitios analizados (P. atricaudus: F'ST= 0.013 - 0.017, P > 0.05, D'est= -0.004 - 0.023, P > 0.05; P. magnus: F'ST= 0.031, P= 0.055; D'est= 0.045, P= 0.058). Este trabajo representa la primera aproximación a la diversidad y genética poblacional de especies de la familia Pseudopimelodidae y proporciona un marco de referencia para futuros estudios genético-poblacionales y de conservación, requeridos en esta familia de bagres poco estudiada en el nivel microevolutivo.(AU)