Dams cause genetic homogenization in populations of fish that present homing behavior: Evidence from a demogenetic individual-based model

Abstract Few studies have assessed the impact of dams on the distribution of the genetic diversity of Neotropical fish species, and some of them suggest that the genetic structure of fish metapopulations is not affected by damming. However, the effects of dams on the genetic structure of populations may hinge on the biological characteristics of the species, such as homing behavior. Dams prevent some individuals from migrating from their feeding area to their natal spawning area, constraining them to reproduce in the tributaries that are closest to the barrier, and which are already being used as breeding grounds by other subpopulations. In these places, subpopulations may interbreed, thus disrupting the overall genetic structure of the metapopulation. To test this hypothesis, we developed a demogenetic Individual-Based Model that simulates the impact of permeable and impermeable dams on the genetic structure of homing populations, in both the long-term and the short-term. Our results support that genetic homogenization occurs among the subpopulations in the short-term, especially near the dam. The impact of a dam on the genetic structure is also detectable in the long-term (100 generations after the addition of the dam) when the dam is permeable (symmetrical or asymmetrical). However, when the barrier is not permeable, the genetic differentiation among the subpopulations is reestablished in the long-term. Our results suggest that conservation programs should be developed to avoid/mitigate genetic homogenization of populations of fish that display homing behavior in the short-term, and to reestablish the pre-dam genetic structure of these populations in the long-term.