Quantifying fitness benefits of polyandry in Atlantic salmon

为什么这么多物种的雌性与多个雄性交配，当它们从这种“一妻多夫制”中除了精子之外什么也得不到，而只与一个雄性交配就足以确保完全的生育能力？这在进化生物学中仍然是一个持久的问题，因为当雌性繁殖交配时，已经测量了显着的成本。我们现在知道，在交配和受精之间的配子水平上运作的机制比以前想象的要复杂得多。在一妻多夫制下，随着更大和更多样化的精子群体竞争受精，有更多的选择性适应机会，促进精子竞争能力，和/或神秘的女性选择。最近的实验研究表明，一妻多夫制允许女性在配子水平上为后代“捕获”遗传利益。这种好处可能是因为精子质量和一般健康之间的联系，或者因为女性已经进化出允许选择携带内在上级基因或未受损DNA的精子的机制，或者可能存在对携带与女性/卵子基因型更相容的基因的精子的神秘选择。我们建议量化一妻多夫制的好处，在一个系统中使用精心控制的体外受精，以创建后代批次从同一个女性，只根据他们是否单独受精由五个单独的男性，或由相同的五个男性，但在同时精子竞争。我们的实验模型将是大西洋鲑鱼，其中女性自然交配多达16男性一次，并在外部受精允许我们进行体外受精，控制或消除一些重要的混淆影响后代的健身，如偏见或可变的母体投资卵子质量。我们之前对鲑鱼体外受精动力学的研究将使我们能够确保生育力不是每个卵批次的限制因素。对于每只雌性，我们将创建5个卵子批次，这些卵子批次由来自5个不同的单一雄性的精子受精（=单雄条件），以及5个卵子批次，这些卵子批次由来自相同5个雄性的精子的均质混合物受精（=一妻多夫条件）。这些配对比较将重复25次，使用25只雌性和125只雄性。该设计将控制成虫身份和卵子效应，并产生仅在存在或不存在精子竞争和/或卵子选择的情况下根据受精而不同的后代批次。受精后，将在胚胎发育、卵孵化、卵发育、鱼苗出苗和幼仔存活、成功和生长的关键阶段测量后代批次的存活和生长。这些健康措施将全部在实验性河段进行，以便进行与环境相关的选择。利用挪威的伊姆斯鲑鱼野外站，将提供能够进行实验控制的设施，同时在半自然条件下饲养鲑鱼卵和鱼苗，并从对鲑鱼卵、胚胎、鱼苗和幼鱼进行操作的许多正常力量中进行选择。我们必须在自然环境中进行选择的条件下测量卵子和后代的表现，因为这是适应性益处最重要的地方。在项目结束时，我们将测量在一妻多夫制下可以获得哪些健身益处，以及这些益处发生在鲑鱼的生命阶段。研究结果对于全面了解一妻多夫制的遗传益处至关重要。重要的是，我们的工作将适用于鲑鱼孵化场育种策略的相关性。为了保护遗传多样性，孵化场协议现在使用强制一夫一妻制，以最大限度地增加参与繁殖的雄性繁殖者的数量。然而，可能有重要的一妻多夫制的好处被排除在这些协议之外，我们的项目将衡量这些好处的重要性。

Why do females of so many species mate with multiple males, when they gain nothing from this 'polyandry' apart from spermatozoa, and mating with only one male is sufficient to ensure full fertility? This remains an enduring question in evolutionary biology, because significant costs have been measured for females when they multiply mate. We now know that the mechanisms operating at the gamete level between mating and fertilization are much more complex than previously supposed. Under polyandry, with bigger and more diverse populations of spermatozoa competing for fertilization, there is even more selective opportunity for adaptations that promote sperm competitive ability, and / or cryptic female choice. Recent experimental research suggests that polyandry allows females to 'capture' genetic benefits at the gamete level for their resulting offspring. Such benefits may arise because of links between sperm quality and general fitness, or because females have evolved mechanisms that allow selection of sperm that carry intrinsically superior genes or undamaged DNA, or there may be cryptic choice for sperm that carry genes that are more compatibile to the female/egg genotype. We propose to quantify benefits of polyandry in a system using carefully controlled in vitro fertilizations to create offspring batches from the same female that only differ according to whether they were fertilized by five separate males singly, or by the same five males but in simultaneous sperm competition. Our experimental model will be the Atlantic salmon, in which females naturally mate with up to 16 males at once, and where external fertilization allows us to conduct in vitro fertilizations that control or eliminate a number of important confounding effects on offspring fitness, such as biased or variable maternal investment in egg quality. Our previous work on salmon in vitro fertilization dynamics will allow us to ensure that fertility is not a limiting factor for each egg batch. For each female, we will create 5 egg batches which were fertilized by sperm from 5 different, single males (=monandrous condition), and 5 egg batches that were fertilized by homogenised mixes of sperm from the same 5 males (= polyandry condition). These paired comparisons will be repeated 25 times, using 25 females and 125 males. The design will control for adult identity and egg effects, and generate offspring batches that only differ according to fertilization in the presence or absence of sperm competition and/or egg choice. After fertilization, the offspring batches will be measured for survival and growth across key stages of embryo development, egg hatch, alevin development, fry emergence, and parr survival, success and growth. These fitness measures will all be conducted in experimental stream sections that allow environmentally-relevant selection to operate. Use of the Ims salmon field station in Norway will provide access to facilities that enable experimental control, while rearing eggs and fry in semi-natural conditions with selection from many of the normal forces that operate on salmon eggs, embryos, fry and parr. It is essential that we measure egg and offspring perfomance under conditions that present some selection from the natural environment, because this is where fitness benefits will be most important. At the conclusion of the project, we will have measured what fitness benefits can be gained under polyandry, and what life stages these gains occur in salmon. The results will be of central importance to a pure understanding of the genetic benefits of polyandry. Importantly, our work will have applied relevance for salmon hatchery breeding strategies. To conserve genetic diversity, hatchery protocols now use enforced monogamy to maximize the number of male breeders involved in reproduction. However, there may be important polyandry benefits that are excluded by these protocols, and our project will measure how important these benefits might be.