The revolution that has taken place in molecular biology over the past decade has revealed one of nature's best kept secrets, namely, that females across a wide range of animal species commonly mate with more than one male. Identifying the causes and consequences of such polyandrous behavior is of general significance to a broad spectrum of biological disciplines, ranging from developmental and conservation genetics to the study of new species formation. Unfortunately, however, the technical difficulties associated with evaluating the alternative material and genetic benefit hypotheses that have been proposed to explain polyandry make investigation of this behavior largely intractable in many species.
The development of powerful, polymerase chain reaction (PCR) techniques for assigning paternity, in combination with a unique suite of reproductive and behavioral characteristics, make the pseudoscorpion, Cordylochernes scorpioides, a model invertebrate organism for experimental investigation of the selective forces favoring polyandry. Accurate assessment of female sexual receptivity in these pseudoscorpions is greatly facilitated by their indirect method of sperm transfer via a spermatophore deposited on the substrate. Female reproductive status and embryonic development can be readily monitored without the need for invasive techniques, due to Cordylochernes scorpioides' "external womb" form of viviparity (live birth), in which females nourish embryos in an external, translucent brood sac overlying the genital aperture. In addition, these pseudoscorpions produce large broods, have a rapid generation time, and are highly amenable to large-scale, laboratory behavioral, rearing and genetic studies of individuals derived directly from natural populations.
Previous research has established that polyandry in Cordylochernes scorpioides significantly enhances female lifetime reproductive success, and that it is an active strategy in which females recognize and reject previous mates. Over their lifetime, females mated to two different males gave birth to 32% more offspring than did females mated twice to the same male. This was primarily as a consequence of a significantly reduced rate of spontaneous abortion, strongly suggesting that polyandry reduces the risk and/or cost of fertilization by genetically incompatible sperm. The goal of the proposed research is to gain a better understanding of the behavioral and physiological mechanisms underlying polyandry in Cordylochernes scorpioides. A combination of behavioral experiments and molecular techniques will be used to address the following questions:
1. What is the recognition mechanism used by females to discriminate against previous mates and preferentially accept sperm from novel males in order to access the reproductive benefits of polyandry? 2. To what extent is the enhanced lifetime reproductive success of polyandrous Cordylochernes scorpioides females due to 'cryptic material benefits' deriving from a rescuing effect of multi-male seminal fluid products, as opposed to post-mating mechanisms that bias paternity in favor of more compatible or genetically superior males? 3. To what extent do processes acting prior to fertilization (sperm competition and/or female choice of sperm) versus processes acting after fertilization has occurred (reallocation of maternal resources from defective/inferior embryos to viable/superior embryos during gestation) contribute to paternity biasing in polyandrous females?
As the first study to investigate the relative importance of pre- versus post-fertilization paternity-biasing mechanisms in a live-bearing species, the findings of this research should contribute to a better understanding of the role that reproductive mode may play in the evolution of female mating behavior.
