POST-INSEMINATION SIGNALING SYSTEMS AND REINFORCEMENT

Theory indicates that the conditions necessary for the operation of re inforcement are very restrictive, yet two recent surveys of the litera ture report the widespread occurrence of patterns predicted by the rei nforcement hypothesis. We begin a reconciliation of theory and data by focusing on one of the most troublesome restrictions placed on reinfo rcement: the need for strong selection against hybridization. Laborato ry hybridization studies often do not find evidence of the required se lection. We point out that the design of most laboratory hybridization studies precludes the detection of barriers to fertilization. Recent work on the ground crickets Allonemobius fasciatus and A. socius, whic h we summarize here, suggests that barriers to fertilization evolve qu ickly. If mating is a risky business, such barriers can promote the ev olution of premating isolation. Post-insemination signalling systems a re little understood by evolutionists and worthy of much greater atten tion.