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性状的进化意义。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、水产养殖和保护生物学的原因至关重要。最近对自由产卵者的受精生态学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，卵子和卵皮的大小、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的成功。然而，这些研究并没有解决特定性状是否是受精成功选择的产物，以及这些性状是否作为它们功能相互作用的结果而共同进化。该项目将涉及一组至少9种来自珊瑚礁生态系统的巨刺属（棘皮目：蛇总科）的同域海洋脆星。这一组包括至少40倍的卵子体积变异，为评估大小和其他配子属性在精子-卵子碰撞中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同寻常的物种特异性，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，这尤其激发了我们对这一属的兴趣。该研究将整合系统发育信息、受精性能测试和配子属性测量，以解决有关配子性状进化和共同进化的基本问题。为了在系统发育背景下检验配子功能的假设，本研究有以下四个目标：目的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，以及由于共同祖先而控制性状之间的相关性。目的2：探讨卵子大小和其他配子物理属性在受精中的重要性。体外受精实验和配子性状的变化将用于验证卵子靶大小和精子游动速度对受精成功的种间差异有影响的假设。目的3：探讨精子化学吸引在促进生殖隔离中的作用。目的4：检验配子性状间协方差模式的假设。系统发育信息将用于检验共同进化的假设，其中理论预测了成对性状之间的功能相互作用：卵子大小和果冻外套大小；卵子目标大小和精子速度；精子速度快，寿命长；卵子靶大小与精子趋化性强弱。本研究旨在填补我们对受精生态学和配子性状进化的理解的关键空白。这将是一个全面的研究，在系统发育的背景下，物理和化学性状，可以影响配子接触率。通过对一组生态相似的近亲生物的系统发育信息，本研究明确地测试了关于这些特征之间功能关系的进化假设。此外，该系统中精子趋化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是祖先的受精方式，因此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.