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有着深远的影响。精子通常被认为比卵子便宜，因此很少有人关注它们的最佳分配，或者它们变得有限的可能性。在“廉价精子”物种（如广播产卵者）中，产生了大量精子。然而，不利的物理因素（如稀释）往往导致精子限制和受精成功率低。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（例如，求偶，内部受精），精子限制更可能是由阻碍成功交配的因素引起的。这些生物因素在精子排出之前就起作用了，它们服从于自然选择，并为进化原理提供了证据。为了了解雄性个体行为如何影响种群水平的进程，pi建议研究一种“昂贵精子”物种——蓝蟹（Callinectes sapidus）。他们在大闸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）的雌鱼只有很短的繁殖季节，除非它们活得很长，否则只能产下几窝后代。低纬度地区（佛罗里达）的雌性在漫长的繁殖季节里每年可以生产多达11个卵。在这两种环境中，有足够的精子来实现完全潜在的生育能力的可能性可能是完全不同的。雄性受到不成比例的渔业压力，尤其是在切萨皮克湾。因此，他们是一个大规模实验的参与者，我们打算利用这个实验来更好地了解精子在种群水平上的分配和限制。pi有强有力的初步数据表明，在切萨皮克湾（高纬度，大量捕捞），与捕捞压力较低的佛罗里达相比，雌性精子细胞收到的精子明显较少，雄性输精管明显枯竭。在切萨皮克湾和佛罗里达，生物遥测技术将验证配对和交配发生的地点；野外取样将揭示在交配栖息地中成熟雄性与接受交配的雌性的比例，以及这些雄性必须转移多少精子。实验室和野外实验将测试雄性体型和交配历史对转移精子数量和配偶竞争的影响，是否有一部分精子耗尽的雄性可能主宰交配，以及给定数量的精子能使多少卵/育仔受精。

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.