Testing Hypotheses of Early Arthropod Evolution

9981970 Regier Shultz节肢动物在最近的发育和进化研究中发挥了核心作用，特别是在确定动物之间保守的机制方面。节肢动物应该是同样有价值的多样化研究，鉴于其广泛的形态和生理，他们的物种丰富性，并延伸到寒武纪的化石记录。然而，节肢动物门的多样性（从基因到形态）的研究受到缺乏明确识别的单系群的阻碍。因此，节肢动物进化史的许多基本方面仍然不确定。例如，跨亚门发现的与陆地化相关的形态特征，如呼吸和运动特征，是否代表趋同或共享的衍生特征？节肢动物关系的一个强大的解决方案将代表历史生物学的一个重大进展，并将提供一种测试这些和许多其他进化假说的手段。最近的分子研究，包括我们自己的NSF支持的研究，提供了令人信服的证据，甲壳纲和六足纲（称为Pancrustacea）是密切相关的，反对传统的假设，陆地组六足纲和多足纲更密切相关。 结合我们对螯肢动物门（包括密殖目）和多足动物门单系性的强烈支持，我们现在建议解决Pancrustacea，螯肢动物门和多足动物门之间的基底节肢动物的单系性。 此外，我们建议解决Pancrustacea内的基础关系，特别是放置的六足类相对于甲壳类;目前的分子（和形态学）的证据是没有令人信服的单系甲壳纲。我们目前和拟议的系统发育研究利用核苷酸和推断的氨基酸从多个蛋白质编码，核基因序列，包括延伸因子-1a（1092 nt），RNA聚合酶II（最大亚基，1038 nt至~1600 nt），和延伸因子-2（1899 nt）。其中包括8种六足动物、23种甲壳动物、6种螯肢动物、5种多足动物、9种缓步动物和3种有爪动物。 发表的形态特征矩阵将重新分析，我们强烈支持的分子结果。

9981970Regier & Shultz Arthropods have played a central role in recent studies of development and evolution, particularly, for identifying mechanisms conserved across animals. Arthropods should be equally valuable for studies of diversification, given their wide range of morphologies and physiologies, their species richness, and a fossil record that extends to the Cambrian. However, studies of diversity (from gene to morphology) across Arthropoda are hindered by the absence of clearly identifiable, monophyletic groups. As a result, many fundamental aspects of arthropod evolutionary history remain uncertain. For example, do suites ofmorphological characters found across subphyla and which are associatedwith terrestrialization, such as features of respiration and locomotion, represent convergences or shared, derived features? A robust resolution of arthropod relationships would represent a major advance for historical biology and would provide a means of testing these and many other evolutionary hypotheses. Recent molecular studies, including our own NSF-supported study,provide compelling evidence that Crustacea and Hexapoda (called Pancrustacea) are closely related, contra the traditional hypothesis that the terrestrial groups Hexapoda and Myriapoda are more closely related. Together with our strong support for the monophyly of Chelicerata (including Pycnogonida) and Myriapoda, we now propose to resolve the basal arthropod trichotomy among Pancrustacea, Chelicerata, and Myriapoda. Additionally, we propose to resolve basal relationships within Pancrustacea, particularly the placement of Hexapoda with respect to the crustacean classes; current molecular (and morphological) evidence is not compelling for a monophyletic Crustacea. Our current and proposed phylogenetic studies utilize nucleotidesand inferred amino acids from multiple protein-encoding, nuclear genesequences, including elongation factor-1a (1092 nt), RNA polymerase II(largest subunit, 1038 nt to ~1600 nt), and elongation factor-2 (1899 nt).Fifty-four species of arthropods and their near-outgroups (i.e., Onychophora and Tardigrada) will be sampled, including 8 hexapods, 23 crustaceans, 6 chelicerates, 5 myriapods, 9 tardigrades, and 3 onychophorans. Published morphological character matrices will be reanalyzed in light of our strongly supported molecular results.