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The process of speciation generates barriers to reproduction that prevent gene flow between diverging populations [1-3]. These isolating mechanisms are distinguished based on the stage of sexual reproduction at which they act. Prezygotic isolating barriers prevent the initial generation of a hybrid zygote. One of the most important prezygotic barriers to reproduction in sexually reproducing animal species is behavioral isolation, which includes factors that reduce the attraction between heterospecific individuals, thus preventing mating [1]. If mating does occur, postmat-ing prezygotic barriers can limit the generation of hybrid offspring [1,4]. These barriers include the precedence of conspecific sperm over heterospecific sperm in female reproductive tracts (e.g. [5]), incompatibilities between sperm and egg surface proteins that prevent fertilizatio