Dissertation Research: The Evolution and Consequences of Variation in Life Histories and Development of Marine Gastropods in the genus Crepidula

9972555沃尔夫和柯林生物群体的物种多样性受到许多不同因素的影响，包括外部（环境）和内部（生理学，生活史）。海洋生物灭绝和多样化的一个关键因素被认为是扩散能力。海洋无脊椎动物（包括海星，蛤和蜗牛）通常从自由漂浮的浮游幼虫阶段发展而来，在行为上可以是摄食或非摄食。这些幼虫为成年期经常定居的动物提供了一种传播途径。然而，有些物种没有经过这样的幼虫阶段（直接发育）。直接发育者在产卵的地方孵化成小型成虫，扩散的可能性很低。具有寄生幼虫的物种和具有直接发育的物种之间的扩散能力的差异与灭绝率的差异和新物种的起源率有关。有浮游幼虫的物种灭绝率较低，不太可能产生新物种。由于扩散能力可能对分类多样性有很大的影响，因此了解扩散能力变化的原因很重要。研究生雷切尔柯林，由顾问博士巴里巴夫在芝加哥大学的指导，正在研究幼虫的发展模式和系统发育关系，在这样一组海洋生物。海蜗牛属（Crepidula）约有50种，其中包括一些直接发育的种类和一些幼虫具有寄生性的种类。该属提供了一个理想的机会，以测试假说的差异，在发展类型的原因。将分析每个物种的三个基因的DNA序列，以确定物种和拟议近亲之间的谱系关系。此外，将在现场观察活动物并描述其发育。这些观察结果将与物种关系的假设相结合，以确定直接发展是否与身体大小，栖息地深度和纬度等生态因素相关。这项研究将确定直接发育的物种的遗传差异是否大于具有寄生幼虫的物种，以及近亲是否比远亲更有可能具有相同的发育类型。这项研究的结果将有助于了解幼虫发育的变化如何影响海洋无脊椎动物群体的多样化或灭绝。

9972555Chernoff and Collin The species diversity of groups of organisms is influenced by many different factors, both external (the environment) and internal (physiology, life history). One key factor in the extinction and diversification of marine organisms is thought to be dispersal ability. Marine invertebrates (including starfish, clams, and snails) typically develop from a free-floating planktonic larval stage, either feeding or nonfeeding in behavior. These larvae provide a means of dispersal for animals that are often sedentary during their adult life. However, some species develop without going through such a larval stage (direct development). Direct developers hatch as miniature adults in the place where the eggs were deposited, and have low potential for dispersal. Differences in dispersal ability between species with planktonic larvae and species with direct development are associated with differences in extinction rates and with the rates of origin of new species. Species with planktonic larvae have lower rates of extinction and are less likely to give rise to new species. Because dispersal ability may have a strong influence on taxonomic diversity, it is important to understand the causes of variation in dispersal ability. Graduate student Rachel Collin, mentored by adviser Dr. Barry Chernoff at the University of Chicago, is studying larval development modes and phylogenetic relationships in one such group of marine organisms. Crepidula, a genus of marine snails with about 50 species, contains some species with direct development and some species with planktonic larvae. The genus offers an ideal opportunity to test hypotheses about the causes of differences in development type. DNA sequences for three genes for each species will be analyzed in order to determine the genealogical relationships among the species and proposed close relatives. In addition, live animals will be observed in the field and their development will be described. These observations will be combined with a hypothesis of species relationships to determine if direct development is correlated with ecological factors like body size, habitat depth, and latitude. This research will determine if genetic differences are greater for species with direct development than for species with planktonic larvae, and if close relatives are more likely to have the same development type than more distant relatives. The results of this research will improve understanding of how changes in larval development affect the diversification or extinction of marine invertebrate groups.