New species arise when populations diverge sufficiently to become reproductively isolated. Is this isolation initiated by barriers to mating and fertilization or by post-fertilization genetic incompatibility? Recent theory suggests that reproductive mode may be a critical factor, with the intimate mother/fetus relationship characteristic of live-bearing (viviparous) species making them far more vulnerable to post-fertilization genetic incompatibility than species that lay eggs. This study will exploit unique reproductive features of a model viviparous invertebrate, the false scorpion Cordylochernes scorpioides, to investigate the role of reproductive mode in speciation. Using population pairs spanning a range of genetic divergence, the research will encompass interpopulation crosses, behavioral experiments, and molecular analyses designed to partition reproductive isolation into mating, gametic, and post-fertilization components to determine the precise sequence through which the various forms of reproductive isolation evolve.
This research will represent the first comprehensive study of speciation mechanisms in a viviparous animal and will shed light on one of the most striking but poorly understood patterns in speciation, namely that lineages differ profoundly in the relative rates at which pre- and post-fertilization isolation evolve. An increased understanding of the evolutionary and mechanistic causes of reproductive isolation in live-bearing species promises to contribute not only to speciation theory but also to studies aimed at identifying and preserving biological diversity.
