Fig. 10.

Semi-permeable species boundaries in Iberian barbels. Species boundaries in Iberian barbels are semi-permeable to gene flow in areas of sympatry after an initial period of allopatric differentiation. Genetic data support a speciation-with-gene-flow scenario with levels of interspecific gene flow inversely associated with divergence, as represented by solid or dashed arrows. Traits involved in ecological preference (e.g. habitat, diet) are likely contributing to reproductive isolation and species coexistence. When these breakdown an ecotype of hybrid origin (L. steindachneri) is formed, frequent in areas with intermediate habitat characteristics