Constraints on Performance and Pelagic Periods of Larvae

幼体性能和远洋周期的限制理查德·R·斯特拉斯曼许多海洋动物以久坐不动的成体形式生活在海床上，但会游泳，并被洋流作为浮游幼体携带。这些幼虫中的许多以摄食为食，在生长数周或数月后才能稳定在底部。幼虫的摄食支持从小卵子到较大尺寸的变态生长。然而，这种支持早期增长和发展的手段是有代价的。幼虫生长的时间越长，它们就会被捕食者吃掉，或者被水流带离海床上栖息地较好的地区。许多幼虫通过集中藻细胞和其他小颗粒的食物来觅食这种食物可能是稀缺的，而且已经证明了食物有限的生长。从悬浮物中浓缩稀有食物的最大速率取决于海洋动物主要类群(门)幼虫的特征。由于食物的供应往往是有限的，人们可能会期待同一水域的幼虫，无论它们有什么其他差异，随着它们重量和能量需求的增加，它们集中稀缺浮游食物的能力会增加，以便在它们发育时获得更大的生长速度。令人惊讶的是，一些动物的幼虫似乎对低浓度食物的适应能力很差。它们浓缩稀缺浮游食物的能力非常有限，即使它们在变态时从微小的卵成长为大得多的幼体。此外，这些幼虫的形态在动物进化的大部分过程中一直保持不变。这项拟议的研究验证了这样一种假设，即食物受限的生长速度取决于幼虫高度保守的特征。预测是，当食物变得更慢时，某些形式的食物尤其会受到限制。这些幼虫中的一些在整个发育过程中都以短纤毛带取食。其中包括苔藓虫的幼虫形式，它们是以岩石和海藻为食的克隆动物，以及线虫(带虫)，它们是其他小型海洋动物的常见捕食者。根据对软体动物和海胆幼虫的广泛研究，苔藓虫和线虫幼虫似乎不符合预测，这对生物学家对浮游幼虫的生态学和进化的理解提出了挑战。苔藓虫幼虫和新月虫幼虫在食物的有限和饱和浓度下的生长将与海豚幼虫的生长相比较，后者从悬浮液中清除食物的最大速率更晚，并且与体重成更接近的比例增加。如果假设是正确的，那么主要动物群体对其幼虫的食物限制是不同的，这会导致它们的死亡率和幼虫的扩散。另一种明显装备不良的摄食幼虫是海葵的平腹幼虫。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，但其中一些在变态之前基本生长。在其他动物群体中，如此简单的幼虫不会捕捉颗粒状食物。对海葵幼虫的摄食能力和生长速度的分析将表明最简单的摄食幼虫的能力。这一结果将表明在其他动物群体中纤毛吸食性幼虫的起源受到限制。

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.