Polyandry: Proximate Mechanisms and Ultimate Causes

分子生物学在过去十年中发生的革命揭示了自然界保守得最好的秘密之一，即在各种动物物种中，雌性通常与不止一只雄性交配。确定这种一夫多妻制行为的原因和后果对从发育和保护遗传学到新物种形成研究等广泛的生物学学科具有普遍意义。然而，不幸的是，与评估替代材料和已提出的解释一夫多妻制的遗传利益假说相关的技术困难使得对许多物种的这种行为的研究在很大程度上是棘手的。强大的聚合酶链式反应(PCR)亲子鉴定技术的发展，与一系列独特的生殖和行为特征相结合，使伪蝎成为一种无脊椎动物模型，用于实验研究有利于一夫多妻制的选择力量。这些伪蝎通过沉积在底物上的精子载体进行精子转移的间接方法，极大地促进了对这些伪蝎雌性性接受能力的准确评估。由于蝎子的“外部子宫”形式的胎生(活产)，雌性可以在不需要侵入性技术的情况下很容易地监测雌性生殖状况和胚胎发育，在这种形式下，雌性在覆盖在生殖器孔上的外部、半透明的孵化囊中滋养胚胎。此外，这些伪蝎子产大窝，世代时间快，对直接来自自然种群的个体进行大规模的实验室行为、饲养和遗传研究。以前的研究已经证实，蝎子的一夫多妻显著提高了雌性一生的繁殖成功，这是雌性识别和拒绝以前配偶的一种积极策略。在它们的一生中，雌性与两个不同的雄性交配产生的后代比与同一雄性交配两次的雌性多32%。这主要是由于自然流产率显著降低的结果，这强烈表明一夫多妻制降低了通过基因不相容的精子受精的风险和/或成本。这项拟议研究的目的是为了更好地了解蝎子一夫多妻制背后的行为和生理机制。将利用行为实验和分子技术相结合的方法来解决以下问题：1.雌性为了获得一夫多妻制的生殖利益而歧视以前的配偶并优先接受新雄性的精子的识别机制是什么？2.多雄的蝎子雌性由于多雄性精液产品的拯救作用而提高了一生的生殖成功，这在多大程度上是因为“隐蔽的物质利益”，3.受精前的过程(精子竞争和/或女性对精子的选择)与受精后的过程(在怀孕期间将母体资源从缺陷/劣质胚胎重新分配到可存活/优势胚胎)在多大程度上导致了一夫多妻制女性的父权偏见？作为第一个研究受精前和受精后父权偏向机制在生育物种中的相对重要性的研究，这项研究的结果应该有助于更好地理解生殖模式在雌性交配行为进化中可能发挥的作用。

IBN-0115986, Lay AbstractThe 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.