First evidence for postzygotic reproductive isolation between two populations of Eurasian perch (Perca fluviatilis L.) within Lake Constance

Background: The evolution of reproductive traits, such as hybrid incompatibility (postzygotic isolation) and species recognition (prezygotic isolation), have shown their key role in speciation. Theoretical modeling has recently predicted that close linkage between genes controlling pre- and postzygotic reproductive isolation could accelerate the conditions for speciation. Postzygotic isolation could develop during the sympatric speciation process contributing to the divergence of populations. Using hybrid fitness as a measure of postzygotic reproductive isolation, we empirically studied population divergence in perch (Perca fluviatilis L.) from two genetically divergent populations within a lake. Results: During spawning time of perch we artificially created parental offspring and F(1) hybrids of the two populations and studied fertilization rate and hatching success under laboratory conditions. The combined fitness measure (product of fertilization rate and hatching success) of F(1) hybrids was significantly reduced compared to offspring from within population crosses. Conclusion: Our results suggest intrinsic genetic incompatibility between the two populations and indicate that population divergence between two populations of perch inhabiting the same lake may indeed be promoted by postzygotic isolation.