Phenotypic Plasticity and the Evolution of Marine Invertebrate Larvae

基因在进化中是领导者还是追随者？当玛丽·简·韦斯特-埃伯哈德在十年前提出这个问题时，她把我们的注意力吸引到了一个基本问题上。虽然遗传差异在物种形成中很重要，但大多数生物表现出相当大的表型变异，这种变异不涉及基因序列的变化，而是涉及基因表达的变化。研究基因表达的可遗传变化，被称为表观遗传学，在细胞分化和疾病方面有着悠久的历史。直到最近，表观遗传学工具才被应用于进化的背景下，它正在彻底改变我们对表型多样性起源和持久性的看法。我和我的学生们研究多毛动物（一种海洋无脊椎动物）的表型可塑性。这些物种既能产生小型浮游生物幼虫，也能产生大型底栖动物幼鱼，后代在形态、行为和栖息地上都是二态的。这使我们能够研究形成幼虫形式的进化转变的机制，具有广泛的意义，因为大多数后生动物都产生幼虫阶段。我建议研究表观遗传学在这种情况下表型可塑性的潜在作用。表观遗传机制，如组蛋白和DNA甲基化，是快速的，可逆的，对环境有反应的，能够产生可代代相传的替代表型。我们将通过以下方法来验证幼虫发育中的二态性是通过表观遗传学进化的假设：1)利用免疫组织化学将组蛋白修饰的差异映射到幼虫形态之间的表型差异；2)利用原位杂交技术研究胚胎的新生甲基化事件，以确定幼虫形态在发育过程中何时建立；3)确定线虫栖息地中作为表观遗传标记并改变幼虫形态和生活史的因素。这将是极少数研究环境与非模式物种表型之间的分子联系的研究之一。这项研究将为年轻科学家在一个令人兴奋的新兴领域提供宝贵的培训机会。

Are genes leaders or followers in evolution? When Mary Jane West-Eberhard posed this question a decade ago, she drew our attention to a fundamental point. While genetic divergence is important in speciation, most organisms exhibit considerable phenotypic variation that does not involve changes in gene sequence, but rather changes in gene expression. The study of heritable changes in gene expression, termed epigenetics, has a long history in cell differentiation and disease. Only recently have epigenetic tools been applied within an evolutionary context, and it is revolutionizing our ideas on the origins and persistence of phenotypic diversity.My students and I study phenotypic plasticity in polychaetes, a group of marine invertebrates. These species produce both small planktonic larvae and large benthic juveniles, offspring that are dimorphic in morphology, behavior and habitat. This allows us to investigate the mechanisms that shape evolutionary transitions in larval form, with broad implications as the majority of Metazoa produce a larval stage. I propose to investigate the potential role of epigenetics in this case of phenotypic plasticity. Epigenetic mechanisms, such as histone and DNA methylation, are fast, reversible, responsive to environment and capable of producing alternate phenotypes that can be passed down over generations. We will test the hypothesis that dimorphisms in larval development evolved through epigenetics by: 1) using immunohistochemistry to map differences in histone modifications to differences in phenotype between larval morphs; 2) using in situ hybridization to study de novo methylation events in embryos to identify when larval morph is established in development; and, 3) identifying factors in the worms' habitat that act as epigenetic marks and change the morphology and life history of young. This will be one of very few studies to investigate the molecular link between environment and phenotype in a non-model species. This research will provide valuable training opportunities for young scientists in an exciting and newly emerging field.