Facultative Feeding by Planktotrophic Larvae of Echinoids

要提高我们对海洋生物繁殖和发育生态学的认识，就需要把生活史理论与作为远洋生物的幼虫的功能分析结合起来。这种结合应该证明是这些领域之间重要的综合联系。一个核心问题是什么生态因素会影响取食幼虫的发育？对能量学的关注是重要的，因为这是许多生命史、生态学和进化的一般理论模型的核心。该项目将通过评估一种密切相关的、共同发生的、卵大小差异很大的棘蚴群的兼性摄食的后果，为浮游营养化幼虫的发育提供新的信息。传统上，海洋无脊椎动物的幼虫被分为两种相互排斥、质量不同的营养类型：摄食和非摄食。大多数需要食物发育的幼虫被认为来自非常小的卵，并且在幼虫的一生中都需要食物。非摄食幼虫由非常大的蛋黄蛋发育而成，直到变态后才能获得或利用外源食物。许多生活史性状与营养模式有关，如卵的大小、繁殖力、幼虫的形态、发育时间和幼鱼的大小。生活史特征分布的经验观察和幼虫策略的理论建模表明，这两种营养模式的极端代表了最成功的繁殖策略。近年来对棘刺类动物幼虫摄食需求的研究挑战了经典的海洋无脊椎动物繁殖策略模型的预测。一系列令人惊讶的“中间”策略，以前没有被认识到，也没有被预测到，已经被记录下来。在棘足类动物（海胆和沙美元）中，存在连续的摄食策略，幼虫在发育到变态所需食物的程度上有很大的不同。卵中由亲本提供的营养储备的数量与幼虫需要外源食物的阶段呈正相关。据预测，鸡蛋的能量含量也决定了兼性摄食的能力，即在内源储备耗尽和必须摄食之前获取外源食物的能力。关于兼性幼虫摄食的信息的缺乏妨碍了对幼虫策略差异的生态和进化意义的有意义的评估。该项目旨在评估兼性摄食对浮游营养型棘卵类幼虫的贡献。将采用两种方法。首先，通过实验室实验，对6种不同卵大小和不同发育能力的共生物种的兼性摄食对幼虫发育率和幼鱼能量含量的贡献进行了实证评估。其次，建立新的幼虫发育和生长理论模型，分析兼性取食对不同亲本投入水平相对优势的影响。这些研究旨在为海洋无脊椎动物幼虫策略多样性背后的关系提供新的信息。

McEdward Advances in our understanding of the ecology of reproduction and development in marine organisms require combining life history theory with functional analyses of larvae as pelagic organisms. This combination should prove to be an important integrative link between these fields . A central question will be what ecological factors influence the development of feeding larvae? A concentration on energetics is important because this is central to many general theoretical models of life history ecology and evolution. This project will provide new information on the development of planktotrophic larvae by evaluating the consequences of facultative feeding in a closely related, co-occurring group of echinoids that differ widely in egg size. Traditionally marine invertebrate larvae have been classified into two mutually exclusive, qualitatively different nutritional types: feeding and non-feeding. Most larvae that require food for development are thought to come from very small eggs and require food throughout larval life. Non-feeding larvae develop from very large yolky eggs and cannot obtain or utilize exogenous food until after metamorphosis. Many life history traits are correlated with nutritional mode, such as egg size, fecundity, larval morphology, development time, and juvenile size. Empirical observations of the distribution of life history traits and theoretical modeling of larval strategies have led to the view that the extremes of the two nutritional patterns represent the most successful reproductive strategies. Recent work on the feeding requirements of echinoid larvae challenges the predictions made by the classic models of reproductive strategies in marine invertebrates. A surprising range of "intermediate" strategies that had not been recognized before, nor predicted, has been documented. Among echinoids (sea urchins and sand dollars) there exists a continuum of feeding strategies across which larvae vary substantially in the degree to which they require food for development to metamorphosis. The amount of nutritional reserves provided in the egg by the parent is positively correlated with the stage at which the larvae require exogenous food. It is predicted that egg energy content also determines the capacity for facultative feeding, i.e., the ability to acquire exogenous food before endogenous reserves are exhausted and feeding becomes obligatory. The lack of information on facultative larval feeding precludes a meaningful assessment of the ecological and evolutionary implications of differences in larval strategies. The project seeks to assess the contribution of facultative feeding in planktotrophic echinoid larvae. Two approaches will be used. First, laboratory experiments will be used to evaluate empirically the contribution of facultative feeding to larval development rate and juvenile energy content in six related, co-occurring species that have different egg sizes and different abilities to develop in the absence of food. Second, new theoretical models of larval development and growth will be constructed to analyze the consequences of facultative feeding on the relative advantages of different levels of parental investment. These studies are designed to generate new information on the relationships that underlie the diversity of larval strategies among marine invertebrates.