Downstairs gene flow: the effects of a linear sequence of waterfalls on the only population of the endangered minnow Astyanax xavante.

The aim of this study was to estimate the genetic diversity and structure of the only known population of minnow Astyanax xavante, which inhabits a stretch of river including several waterfalls. The FST values among the samples were not significant, except between two populations separated by a 30 m waterfall. Nevertheless, haplotype and nucleotide diversity increased in the downstream direction, indicating that gene flow is unidirectional, which indicates this genetic pattern as downstairs gene flow, as it has the effect of increasing genetic diversity in the downstream direction.