Collaborative Research: Reproductive Ecology in the Blue Crab, Callinectes Sapidus

雄性动物在繁殖方面的投资对交配制度和个体行为产生了深远的影响。精子通常被认为比卵子便宜，因此相对较少的注意力被投入到它们的最佳分配上，或者它们变得有限的可能性。在“廉价精子”物种(例如广播产卵者)中，会产生大量的精子。然而，不利的生理因素(如稀释)往往会导致精子受限和受精成功率不佳。在“昂贵的精子”物种中，大量投资于提高精子转移可靠性的机制(如求偶、内部受精)，精子限制更有可能是由阻碍成功交配的因素造成的。这些生物因素在精子排出之前起作用，受到自然选择的影响，并提供了进化原理的证据。为了了解雄蟹的个体行为如何影响种群水平的过程，PI们建议研究一种“昂贵的精子”物种--蓝蟹(Callinectes Sapidus)。他们在螃蟹的纬度范围内选择了两个相距很远的研究地点，这两个地点对交配系统施加了非常不同的条件。高纬度地区(切萨皮克湾)的雌性恐龙繁殖季节很短，除非寿命很长，否则只能产下几窝幼崽。低纬度(佛罗里达)的雌性在漫长的繁殖季节每年可产下多达11窝幼崽。在这两种环境中，有足够的精子来实现完全的潜在繁殖力的可能性可能是截然不同的。雄性受到不成比例的渔业压力，特别是在切萨皮克湾。因此，他们是一项大规模实验的参与者，我们建议利用该实验来更好地了解精子在种群水平上的分配和限制。PIs有强有力的初步数据表明，在切萨皮克湾(高纬度，高度捕捞)，女性受精囊获得的精子明显较少，而男性输精管明显比佛罗里达州更耗尽，那里的捕鱼压力较低。在切萨皮克湾和佛罗里达的地点，生物遥测将验证交配和交配发生在哪里；野外采样将揭示交配栖息地中成熟雄性和接受雌性的比例，以及这些雄性需要转移多少精子。实验室和野外实验将测试雄性大小和交配历史对转移的精子数量和对配偶竞争的影响，精子枯竭的雄性是否可能主导交配，以及给定数量的精子可以使多少卵/幼体受精。

The investments male animals make in reproduction have profound effects on mating systems and individual behaviors. Sperm generally are considered inexpensive relative to eggs, and hence relatively little attention has been devoted to their optimal allocation, or the possibility that they become limiting. In `cheap sperm` species (e.g. broadcast spawners), huge numbers of sperm are produced. Nevertheless, adverse physical factors (e.g. dilution) often lead to sperm limitation and poor fertilization success. Among `expensive sperm` species that invest heavily in mechanisms to increase the reliability of sperm transfer (e.g., courtship, internal fertilization), sperm limitation is more likely to be caused by factors that hinder successful mating. These biological factors, acting before sperm are emitted, are subject to natural selection and provide evidence of evolutionary principles. To understand how individual behaviors of males affect population-level processes, the PIs propose to study an `expensive sperm` species, the blue crab (Callinectes sapidus). They have chosen two widely-separated study sites in the crabs' latitudinal range, which impose very different conditions on the mating system. High-latitude (Chesapeake Bay) females have only short reproductive seasons and, unless they live very long, can produce only a few broods. Low-latitude (Florida) females can produce as many as 11 broods/year in long reproductive seasons. The probability of sufficient sperm being available to realize full potential fecundity in these two environments probably is quite different. Males are subject to disproportionate fishery pressure, especially in Chesapeake Bay. They thus are participants in a large-scale experiment that we propose to exploit to better understand sperm allocation and limitation at the population level. The PIs have strong preliminary data indicating that in Chesapeake Bay (high latitude, heavily fished), female spermathecae receive significantly less sperm, and male vasa deferentia are significantly more depleted, than in Florida where fishing pressure is lower. At Chesapeake Bay and Florida sites, biotelemetry will verify where pairing and mating occur; field sampling will reveal the ratios of mature males to receptive females in mating habitats and how much sperm those males have to transfer. Laboratory and field experiments will test the effects of male size and mating history on amount of sperm transferred and on competition for mates, whether a subset of sperm-depleted males might dominate mating, and how many eggs/broods can be fertilized by a given amount of sperm.