Dissertation Research: Phylogenetic Origins of Diapause in Marine Harpacticoid Copepods

在假死状态下生存的能力通常被称为休眠或滞育。真菌和细菌的孢子，高等植物的种子，某些昆虫的幼虫，以及一些甲壳类动物的包囊，特别是盐水虾（Artemia），是生物体中较著名的滞育阶段的例子。在甲壳类动物（螃蟹、龙虾、虾和它们的近亲）中，那些生活在内陆水域的动物，尤其是那些偶尔结冰或干燥的动物，比生活在海洋中的物种更有可能拥有一个滞育阶段。正如预期的那样，滞育发生在许多被称为羽足类桡足类的小型淡水甲壳类动物身上，但意外的是，它也发生在至少两种海洋物种身上。由于海洋环境不太可能冻结或干燥，滞育的好处尚不清楚。海洋物种存在滞育现象可能有三种解释：(1)滞育发生于海洋羽足类桡足类，并在其淡水后代中保留；(2)滞育在淡水羽足类桡足类中出现，并在其海洋后代中保留；(3)滞育分别发生在淡水系和海洋系。在这项研究中，Bruce Coull和博士候选人Regina Wetzer将利用分子和解剖学数据建立属于已知含有滞育物种的科的海洋和淡水桡足类的系统发育关系。这些“家谱”和比较方法将使coulll和Wetzer能够确定密切相关的羽足类桡足类家族的滞育进化史，特别是找出哪种假设最能解释海洋物种的滞育是如何产生的。这项工作可能有助于提供一个更普遍的解释，说明在缺乏冷热季节或干旱季节等波动的稳定环境中，滞育是如何产生的。

9701524 COULL The ability to survive in a state of suspended animation is commonly called dormancy or diapause. The spores of fungi and bacteria, the seeds of higher plants, the larvae of certain insects, and the cysts of some crustaceans, notably the brine shrimp (Artemia), are among the better known examples of diapausing stages in organisms. Among crustaceans (crabs, lobsters, shrimp, and their kin) those inhabiting inland bodies of water, especially those that occasionally freeze or dry, are more likely to possess a diapausing stage than are species living in the ocean. Diapause occurs, as expected, in many species of miniature freshwater crustacea called harpacticoid copepods, but it also occurs, unexpectedly, in at least two marine species. Since the marine environment is not likely to freeze or dry, the benefits of diapause are unclear. Three possible explanations account for the presence of diapause in marine species: (1) diapause arose in marine harpacticoid copepods and was retained in their freshwater descendants; (2) diapause arose in freshwater harpacticoid copepods, and was retained in their marine descendants; (3) diapause arose independently in freshwater and marine lineages of harpacticoid copepods. In this research, Bruce Coull and doctoral candidate Regina Wetzer will use molecular and anatomical data to establish the phylogenetic relationships of marine and freshwater copepods belonging to families known to contain diapausing species. These "family trees" and comparative methods will allow Coull and Wetzer to ascertain the evolutionary history of diapause in closely related families of harpacticoid copepods, and, in particular, to find out which hypothesis best explains how diapause arose in marine qpecies. The work may help provide a more general explanation of how diapause can arise in environments that are OstableO, lacking fluctuations such as Ocold-hotO or Owet-dryO seasons.