Constraints on Performance and Pelagic Periods of Larvae

对仔鱼生长性能和浮游期的限制。斯特拉斯曼 许多海洋动物成年后生活在海床上，但它们会游泳，并作为浮游幼虫被洋流携带。 许多这种幼虫在它们能在海底定居之前会进食并生长数周或数月。幼虫进食支持从一个小卵到变态时的更大尺寸的生长。 然而，这种支持早期生长和发育的手段是有代价的。 幼虫生长的时间越长，被捕食者吃掉的幼虫就越多，或者被水流带离海床上的良好栖息地。 许多幼虫通过浓缩藻类细胞和其他小颗粒食物来进食，这些食物可能很稀缺，并且已经证明了食物有限的生长。 从悬浮液中浓缩稀缺食物的最大速率取决于海洋动物主要类群（门）之间不同的幼虫的特征。 因为食物的供应通常是有限的，所以人们可以预期，在同一沃茨中的幼虫，不管它们有什么其他的差异，随着它们体重和能量需求的增加，为了在发育过程中达到更高的生长速度，它们会增加浓缩稀缺的营养食物的能力。 令人惊讶的是，一些动物的幼虫似乎对低浓度的食物适应不良。 尽管它们在变态期从微小的卵成长为更大的幼鱼，但它们集中稀缺的营养食物的能力非常有限。 此外，这些幼虫形态在动物进化的大部分时间里都没有改变。 这项拟议中的研究验证了一个假设，即食物限制的生长速度取决于幼虫的高度保守特征。 预测是，当食物短缺时，某些形式特别受到限制，生长缓慢。 有些幼虫在整个发育过程中以短纤毛带为食。 这些包括苔藓虫的幼虫形式，它们是生活在岩石和海藻上的非寄生动物，以及纽形动物（带状虫），它们是其他小型海洋动物的常见捕食者。苔藓虫和纽形动物的幼虫似乎不符合基于更广泛研究的软体动物和海胆幼虫的预测，因此挑战了生物学家对浮游幼虫生态学和进化的理解。 苔藓虫和纽形虫幼虫在食物的极限和饱和浓度下的生长将与海胆幼虫的生长进行比较，海胆幼虫从悬浮液中清除食物的最大速率更大，并且几乎与体重成比例地增加。 如果这个假设是正确的，那么主要的动物群体对幼虫的食物限制是不同的，这对幼虫的死亡率和传播产生了影响。 另一种明显装备不良的幼虫是海葵的浮状幼体。 这些幼虫完全没有纤毛带，在解剖学上是最简单的摄食幼虫形式，但其中一些在变态前就已基本生长。 在其他动物群中，如此简单的幼虫不会捕捉颗粒状食物。 对海葵幼体的摄食能力和生长速率的分析将表明最简单的摄食幼体的能力。这些结果将对其他动物类群中纤毛摄食幼虫的起源提出限制。

Constraints on Performance and Pelagic Periods of LarvaeRichard R. Strathmann Many marine animals live on the sea bed as sedentary adults but swim andare carried by ocean currents as planktonic larvae. Many of these larvaefeed and grow for weeks or months before they can settle on the bottom.Larval feeding supports growth from a small egg to a larger size atmetamorphosis. There are costs to this means of supporting early growth anddevelopment, however. The longer the period of larval growth, the morelarvae are eaten by predators or carried by currents away from areas of goodhabitat on the sea bed. Many larvae feed by concentrating algal cells and other small particlesof food This food can be scarce, and food-limited growth has beendemonstrated. Maximum rates of concentrating scarce food from suspensiondepend on traits of larvae that differ among major groups (phyla) of marineanimals. Because food is often in limiting supply, one might expect larvaein the same waters, whatever their other differences, to increase theircapacity to concentrate scarce planktonic food as they increase in weightand energy requirements and in order to achieve greater growth rates as theydevelop. Surprisingly, some animals' larvae appear to be poorly adapted tolow concentrations of food. They have a very limited capacity toconcentrate scarce planktonic food, even though they grow from tiny eggs tomuch larger juveniles at metamorphosis. Moreover, these larval forms haveremained unchanged during much of animal evolution. The proposed research tests the hypothesis that food-limited growthrates depend on highly conserved traits of larvae. The prediction is thatsome forms are particularly constrained to slower growth when food isscarce. Some of these larvae feed with short ciliary bands throughout theirdevelopment. These include the larval forms of bryozoans, which arecolonial animals that live on rocks and seaweeds, and nemerteans (ribbonworms), which are common predators on other small marine animals. Thebryozoan and nemertean larvae do not seem to fit predictions based on themore extensively studied larvae of molluscs and sea urchins and thuschallenge biologists' understanding of the ecology and evolution ofplanktonic larvae. The growth of bryozoan and nemertean larvae at limitingand satiating concentrations of food will be compared to growth of seaurchin larvae, whose maximum rates of clearing food from suspension aregreater and increase more nearly in proportion to body mass. If thehypothesis is correct, then major groups of animals differ infood-limitation for their larvae, with consequences for death rates anddispersal of their larvae. Another case of an apparently ill-equipped feeding larva is the planulalarva of sea anemones. These larvae lack ciliary bands entirely and areanatomically the simplest feeding larval forms, yet some of them growsubstantially before metamorphosis. In other groups of animals, larvae thatare this simple do not catch particulate food. Analyses of feeding capacityand growth rates of larval sea anemones will indicate the capabilities ofthe simplest feeding larvae. The results will indicate constraints on theorigination of ciliated feeding larvae in other groups of animals.