Evolution of development among gastropod molluscs

鲁德亚德·吉卜林的《如此故事》之所以具有持久的吸引力，是因为我们对动植物的奇异特征有着与生俱来的迷恋，也因为我们渴望知道它们来自哪里。苍蝇是怎么长出翅膀的？鸟类的羽毛是怎么来的？对生物体新奇特征的兴趣不仅仅是有趣的娱乐内容。一个有机体是如何获得一个在其他相似的有机体中显然不存在的特征的问题，对进化生物学来说至关重要。新奇的事物让生物学家感到困惑，因为如果自然选择是通过修改先前存在的结构来起作用的，那么看起来新的特征是如何首先形成的呢？解释形态学新奇现象的需要是将发育生物学重新纳入进化生物学的主要推动力。生物学家现在认识到，生物体发育过程中的微小变化，例如结构开始形成时，可以放大为完全形成的生物体中的巨大差异。我用腹足类软体动物作为模型来研究这个巨大的多样化动物群体中新奇事物的发展。我正在研究一个假说，它可以解释腹足类动物高度扭曲的身体结构。腹足类发育的比较研究表明，扭曲可能起源于身体两侧发育的不对称。我还试图解释如何捕食腹足类动物能够发展非常专门的喂养结构，而不影响幼虫阶段的喂养活动。这一问题具有广泛的意义，因为大多数主要的动物群体是无脊椎动物，它们的身体是在包括幼虫阶段的生命周期内建立的。幼虫的需求可能限制了成虫进化的可能性。最后，我问腹足类的游泳幼虫如何获得在变态之前进食和生长的能力。为了研究这些问题，我和我的学生培养了各种各样的海洋腹足类动物，我们使用各种技术进行形态分析，例如扫描和透射电子显微镜，计算机辅助切片材料的3D重建，以及免疫标记来突出感兴趣的结构和细胞。

Rudyard Kipling's Just So Stories have an enduring appeal because of our inherent fascination with bizarre features of animals and plants and our desire to know where they came from. How did flies get their wings? How did birds get their feathers? Interest in novel features of organisms is not only the stuff of quaint entertainments. Questions that ask how an organism acquired a feature that is obviously not present in otherwise similar organisms are of central importance to evolutionary biology. Novelties perplex biologists because, if natural selection works by modifying pre-existing structures, then how do seemingly new characteristics come into being in the first place? The need to explain morphological novelties has been a major impetus for bringing developmental biology back within the embrace of evolutionary biology. Biologists now recognize that small changes during the development of an organism, such as when a structure starts to form, can become magnified into large differences in the fully formed organism. I use gastropod mollusks as a model to study the development of novelties within this hugely diverse group of animals. I am investigating a hypothesis that may explain the highly contorted body plan of gastropods. Comparative studies of gastropod development suggest that the contorsion may have originated as an asymmetry in the development of the two sides of the body. I also seek to explain how predatory gastropods were able to evolve extraordinarily specialized feeding structures without compromising feeding activities of the larval stage. This issue has wide significance because most of the major groups of animals are invertebrates and their bodies are built within a life cycle that includes a larval stage. Needs of the larva may limit possibilities for adult evolution. Finally, I ask how swimming larvae of gastropods acquired the ability to feed and grow prior to metamorphosis. To study these questions, my students and I culture a wide variety of marine gastropods and we use various techniques for morphological analysis, such as scanning and transmission electron microscopy, computer-assisted 3D reconstruction of sectioned material, and immunolabeling to highlight structures and cells of interest.