Collaborative Research: Evolution of Physical and Chemical Attributes of Gametes in Free Spawning Marine Invertebrates: A Functional and Phylogenetic Approach

该项目的目标是研究影响自由产卵海洋生物受精成功的配子特征的进化意义。这一领域的基础研究对于了解收获的无脊椎动物的生殖生态学、水产养殖和保护生物学方面的原因至关重要。最近关于自由产卵生物受精生态的研究提出了关于生命周期配子阶段特征进化的各种问题。理论和实证研究表明，卵子和卵壳的大小、精子受体位置的密度、精子的速度和寿命以及卵子释放的精子激活化合物的作用都可以通过影响精子与卵子的接触率来影响受精成功。然而，这些研究还没有确定特定的性状是否是受精成功的选择的产物，以及这些性状是否似乎是由于它们的功能相互作用而共同进化的。该项目将涉及珊瑚礁生态系统中大型棘皮动物属(棘皮目：眼镜蛇总科)至少9种共地的海洋脆星。这一组包括卵子体积至少40倍的变化，并为评估精子-卵子碰撞中大小和其他配子属性的重要性提供了一个理想的比较系统。我们发现精子趋化性具有不寻常的物种特异性，这为研究精子趋化性在促进生殖隔离中的作用提供了一个独特的机会，这特别激发了人们对该属的兴趣。这项研究将整合系统发育信息、受精性能测试和配子属性测量，以解决配子特征进化和共同进化的基本问题。为了在系统发育的背景下验证关于配子功能的假说，本研究有以下四个目标：目标1：利用分子标记构建研究物种的系统发育。需要系统发育信息来建立性状变化的历史模式，以及控制由于共同祖先而导致的性状之间的相关性。目的：研究卵子大小和其他物理配子属性在受精过程中的重要性。体外受精试验和配子性状变异将被用来检验卵子目标大小和精子游泳速度对受精成功的种间变异的影响这一假说。目的：探讨精子化学引诱在促进生殖隔离中的作用。目的：检验关于配子性状间协方差模式的假设。系统发育信息将被用来检验共同进化的假设，其中理论预测了一对特征之间的功能相互作用：卵子大小和果冻毛大小；卵子目标大小和精子速度；精子速度和寿命；卵子目标大小和精子趋化性的强度。这项研究旨在填补我们在受精生态学和配子性状进化方面的关键空白。这将是一项关于影响配子接触率的物理和化学特征的系统发育背景下的综合研究。通过使用一组密切相关的生态相似生物体的系统发育信息，这项研究明确地测试了关于这些特征之间功能关系的进化假说。此外，该系统中精子趋化性的独特模式为研究接触前化学特异性在促进同步产卵物种的生殖隔离中的作用提供了机会。由于自由产卵是主要的和可能的祖先受精模式，该项目的结果将与海洋环境中生殖系统的进化具有广泛的相关性。

The goal of this project is to examine the evolutionary significance of gamete traits that influence fertilization success in free-spawning marine organisms. Basic research in this field is crucial for understanding the reproductive ecology of harvested invertebrates, for aquaculture and for conservation biological reasons. Recent work on the fertilization ecology of free-spawners has raised diverse questions regarding character evolution at the gamete stage of the life cycle. Theory and empirical studies suggest that the size of eggs and egg coats, the density of sperm receptor sites, the speed and longevity of sperm, and the action of sperm-activating compounds released by eggs can each influence fertilization success by affecting rates of sperm-egg contact. These studies, however, have not resolved whether particular traits are a product of selection on fertilization success, and whether such traits appear to co-evolve as a result of their functional interactions. This project will involve a set of at least 9 sympatric species of marine brittlestars in the genus Macrophiothrix (Echinodermata: Ophiuroidea) from coral reef ecosystems. This group includes at least 40-fold variation in egg volume and provides an ideal comparative system for assessing the importance of size and other gamete attributes in sperm-egg collision. Interest in this genus is especially motivated by our discovery of an unusual degree of species-specificity in sperm chemotaxis, which offers a unique opportunity to examine the role of sperm chemotaxis in promoting reproductive isolation. The research will integrate phylogenetic information, tests of fertilization performance, and measures of gamete attributes to address fundamental questions about the evolution and co-evolution of gamete traits. In order to test hypotheses about gamete function in a phylogenetic context, this study has the following four objectives: OBJECTIVE 1: To construct a phylogeny for the study species using molecular markers. Phylogenetic information is needed to establish historical patterns of character change, as well as to control for correlation among traits due to common ancestry. OBJECTIVE 2: To examine the importance of egg size and other physical gamete attributes in fertilization. In vitro fertilization assays and variation in gamete traits will be used to test the hypothesis that egg target size and sperm swimming speed contribute to interspecific variation in fertilization success. OBJECTIVE 3: To examine the role of spermegg chemical attraction in promoting reproductive isolation. OBJECTIVE 4: To test hypotheses concerning patterns of covariance among gamete traits. Phylogenetic information will be used to test hypotheses of coevolution where theory predicts functional interactions between pairs of traits: ovum size and jelly coat size; egg target size and sperm speed; sperm speed and longevity; egg target size and the strength of sperm chemotaxis. This research is designed to fill critical gaps in our understanding of fertilization ecology and the evolution of gamete characters. This will be a comprehensive study in a phylogenetic context of both physical and chemical traits that can influence rates of gamete contact . By using phylogenetic information for a closely-related group of ecologically similar organisms, this research explicitly tests evolutionary hypotheses about functional relationships among such traits. Furthermore, the unique pattern of sperm chemotaxis in this system provides an opportunity to examine the role of pre-contact chemical specificity in promoting the reproductive isolation of synchronously-spawning species. Because free-spawning is the dominant and likely ancestral mode of fertilization, results from this project will have widespread relevance to the evolution of reproductive systems in marine environments.