Evidence of parental care as a novel reproductive isolating mechanism

Variation in behavior can contribute to reproductive isolation by preventing gene flow among populations. Here, we tested the novel hypothesis that parental care, when dysregulated, can act as a reproductive isolating mechanism in three-spined stickleback fish (Gasterosteus aculeatus). In the typical "common" stickleback ecotype, males provide care to their offspring through pectoral fanning and nest attendance. In contrast, a divergent "white" stickleback ecotype has evolutionarily lost care and disperses embryos into the surrounding environment. We examined how paternal care from common, white, and F1 hybrid fathers influenced the survival of offspring. We detected no intrinsic incompatibilities in embryos, but hybrid fathers exhibited dysregulated parental care and increased rates of filial cannibalism. These results may explain why genetic divergence between these phenotypically distinct ecotypes is so low and provide evidence that dysregulated parental behavior can cause behavioral sterility and thereby act as a novel postzygotic reproductive isolating barrier.