Evolution of development among gastropod molluscs

拉迪亚德·吉卜林（Rudyard Kipling）的《如此故事》（Just So Stories）具有持久的吸引力，因为我们对动物和植物的奇异特征有着与生俱来的迷恋，我们渴望知道它们来自哪里。苍蝇是怎么得到翅膀的？鸟的羽毛是怎么来的？对生物体新特征的兴趣不仅仅是古怪的娱乐。对于进化生物学来说，一个生物体是如何获得一个在其他类似生物体中明显不存在的特征的问题是至关重要的。新颖性让生物学家感到困惑，因为如果自然选择是通过修改已有的结构来实现的，那么最初看似新的特征是如何产生的呢？解释形态上的新奇性的需要一直是将发育生物学带回进化生物学怀抱的主要推动力。生物学家现在认识到，在一个有机体的发育过程中，比如当一个结构开始形成时，微小的变化可以被放大，在完全形成的有机体中形成巨大的差异。我用腹足类软体动物作为模型来研究这一种类繁多的动物群体的新奇发展。我正在研究一种假说，可以解释腹足类动物高度扭曲的身体结构。腹足动物发育的比较研究表明，这种扭曲可能起源于身体两侧发育的不对称。我还试图解释掠食性腹足类动物如何能够进化出非常专门的摄食结构，而不影响幼虫阶段的摄食活动。这个问题具有广泛的意义，因为大多数主要的动物群体都是无脊椎动物，它们的身体是在一个包括幼虫期在内的生命周期内形成的。幼虫的需要可能限制成虫进化的可能性。最后，我问游泳的腹足类幼虫在变态之前是如何获得觅食和生长的能力的。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类动物，我们使用各种形态学分析技术，如扫描和透射电子显微镜，计算机辅助的三维重建切片材料，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.