A fractal pattern of hierarchical genetic population structure in mixed stocks across fish segregated by dams revealed by genomic resources for curimba Prochilodus lineatus

Genomic resources, new microsatellite markers and a novel observation of a fractal pattern of the genetic population structure are presented for curimba Prochilodus lineatus , a suitable model organism for freshwater migratory species in South America. Our main goals were to investigate the presence of mixed fish stocks, the effects of isolation by dams and broodstocking over the genetic diversity for this species. We focused on the upper segment of the extremely fragmented Grande River, MG, Brazil, from the megadiverse continental La Plata Basin. Two main co-occurring genetically admixed stocks were identified by maximum likelihood estimation and iteratively unfolded with two further steps, through a hierarchical analysis of genetic structure. It consistently unveiled two newly defined internal groups, from the previously resolved clusters (2³). We suggest this stratified pattern of mixed stocks from the main river channel may be attributed to the existence of different, well defined breeding grounds, nested within differential scales throughout this basin, arranged according to fractal geometry (1 ^st order river, 2 ^nd and 3 ^rd order tributaries, and so on). This would imply in homing behaviour for this species. Our work also provides massive molecular data for this fish, including its first draft genome assembly and a valuable panel for the rapid and low-cost development of new microsatellite DNA markers. These findings will likely benefit researchers and environmental managers in tackling challenging issues regarding the conservation of Neotropical migratory fishes, as they support the hypothesis of the isolating effects of dams and broodstocking over genetic variability. More importantly, the results presented here point to the potential role of tributaries of different orders in harbouring genetically diverse populations of migratory freshwater fishes.