Evolutionary transitions between different modes of development in marine invertebrates are thought to be biased toward the loss of feeding larvae. Because the morphology of feeding larvae is complex and nonfeeding larvae or encapsulated embryos with benthic development often have simplified morphologies, it is presumed to be easier to lose a larval stage than to reacquire it. Some authors have gone so far as to suggest that feeding larvae, morphologically similar to the ancestral feeding larvae, cannot be reacquired. However, the larval structures of some groups, most notably gastropods, are often retained in the encapsulated embryos of species that hatch as benthic juveniles. Therefore the re-evolution of feeding larvae using the same structures may be possible in these groups. Here we present the first well-substantiated case for the recent re-evolution of feeding larvae within a clade of direct-developers. DNA sequence data show that Crepipatella fecunda, a species of calyptraeid gastropod with planktotrophic development, is nested within a clade of species with direct development, and that Crepipatella dilatata, a species with direct development, appears to be paraphyletic with respect to C. fecunda. Observation of the embryos of C. dilatata shows that the features necessary for larval feeding and swimming are retained in the encapsulated veligers, suggesting that heterochronic shifts in hatching time and changes in nurse-egg allotment could have resulted in the re-evolution of feeding larvae in this species.

译文

:海洋无脊椎动物不同发育方式之间的进化过渡被认为倾向于减少幼体的摄食。由于喂食幼虫的形态很复杂,并且不喂食幼虫或底栖发育的包囊胚胎通常具有简化的形态,因此推测失去幼虫阶段要比重新获得幼虫容易。一些作者甚至提出,不能重新获得形态上类似于祖先喂养幼虫的喂养幼虫。然而,某些群体的幼虫结构,最著名的是腹足动物,通常保留在作为底栖幼体孵化的物种的包囊胚胎中。因此,在这些组中使用相同的结构重新喂养幼虫是可能的。在这里,我们提出了第一个充分证实的案例,该案例是近期在直接开发者群体中喂食幼虫的重新进化。 DNA序列数据表明,具有浮游营养发育的ca蝶腹足纲动物的一种种,Cappipatella fecunda被嵌套在具有直接发育的种的进化枝中,而具有直接发育的物种,Crepipatella dilatata似乎与费氏梭菌具有共生性。观察C. dilatata的胚胎表明,幼虫的摄食和游泳所必需的特征保留在包囊的飞虱中,这表明孵化时间的异时变化和护士卵的分配变化可能导致了摄食幼虫的重新进化。在这个物种中。

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