Evolution of development among gastropod molluscs

鲁迪亚德·吉卜林的小说《就是这样》具有持久的吸引力，因为我们天生就对动物和植物的奇特特征着迷，而且我们渴望知道它们是从哪里来的。苍蝇是如何长出翅膀的？鸟是怎么长出羽毛的？对生物新奇特征的兴趣不仅仅是一种奇特的娱乐。对于进化生物学来说，询问有机体如何获得在其他类似生物体中显然不存在的特征的问题是至关重要的。新奇之处困扰着生物学家，因为如果自然选择是通过改变现有的结构来发挥作用的，那么看似新的特征是如何首先产生的？解释形态新颖性的需要一直是将发育生物学重新纳入进化生物学怀抱的主要推动力。生物学家现在认识到，生物体发育过程中的微小变化，如结构开始形成的时候，可以放大为完全形成的有机体中的巨大差异。我以腹足类软体动物为模型，研究在这一极其多样化的动物群体中，新奇事物的发展。我正在研究一个假说，这个假说可能可以解释腹足动物高度扭曲的身体结构。对腹足动物发育的比较研究表明，这种扭曲可能源于身体两侧发育的不对称。我还试图解释捕食性腹足动物是如何在不影响幼虫阶段摄食活动的情况下进化出非常专门的摄食结构的。这个问题具有广泛的意义，因为大多数主要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。幼虫的需求可能会限制成虫进化的可能性。最后，我问腹足类游泳幼虫在变态之前是如何获得摄食和生长能力的。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动物，我们使用了各种形态分析技术，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.