Dissertation Research: Phylogenetic Origins of Diapause in Marine Harpacticoid Copepods

9701524在假死状态下存活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，特别是卤虫，都是生物体中更著名的滞育阶段的例子。在甲壳类动物(蟹、龙虾、虾及其近亲)中，居住在内陆水体中的物种，特别是那些偶尔结冰或干燥的物种，比生活在海洋中的物种更有可能处于滞育阶段。不出所料，许多小型淡水甲壳类动物都会发生滞育，这些物种被称为直腹鳍足类动物，但出人意料的是，至少有两个海洋物种也发生了滞育。由于海洋环境不太可能结冰或干燥，滞育的好处尚不清楚。对海洋物种中滞育现象的存在有三种可能的解释：(1)滞育发生在海洋尺足类动物中，并保留在它们的淡水后代中；(2)滞育出现在淡水尺足类动物中，并保留在它们的海洋后代中；(3)滞育独立地出现在淡水和海洋中的尺足类动物谱系中。在这项研究中，Bruce Coull和博士生Regina Wetzer将使用分子和解剖学数据来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“系谱”和比较方法将使Coull和Wetzer能够确定近缘的响尾龙桡足动物家族中滞育的进化史，特别是找出哪种假说最好地解释了海洋q种的滞育现象。这项工作可能有助于提供一个更一般的解释，解释滞育是如何在没有波动的环境中产生的，比如冷季或旱季。

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.