Comparative population genomics of Pimelodus yuma and Pimelodus grosskopfii in the Neotropical Magdalena Cauca river basin

The Magdalena and Cauca are independent rivers conforming the Magdalena-Cauca Basin in Colombia, whose geological formation dates back to 33 million years ago. The total extension of this basin covers approximately ~1,600 km with sloped (Cauca) and flat (Magdalena) areas, within which 213 species of fish have been identified, of which 50% are endemic. Pimelodus yuma stands out as a species of great importance for artisanal fishing. This species exhibits medium and local migrations, covering distances between 50 and 100 km, being documented in the middle and upper Magdalena River but not in the Cauca River. In the case of Pimelodus grosskopfii, it is listed as one of the 30 most important commercially traded species within the basin. This species has been sighted in both Rivers, including the lower, middle, and upper Cauca, as well as the middle and upper Magdalena. However, P. grosskopfii seems to exhibit a pattern of medium migration, according to the ecological evidence.Considering the above migration patterns and the great geographical extent of the basin, we tested the hypothesis of panmixia Vs. structured patterns in these species, and evaluated their historical demography. For this, RADseq markers were analyzed from each species along the basin using coalescence-based and allele-frequency methods.Phylogeographic, structure, and Principal component analysis revealed the presence of panmixia in both species. Contrary to expectations, it was identified one individual of P. yuma in the Upper Cauca, and the presence of P. grosskopfii individuals in the lower Magdalena. A pronounced population expansion was detected for both species from 1.5 mya (P. groskopffii) and 1 mya (P. yuma), until the present.In summary, the results suggest that both P. yuma and P. grosskopfi exhibit greater mobility and geneflow than previously believed within the basin, likewise a healthy expansion of its effective size. Additionally, the presence of both species in areas that were not