Testing Hypotheses of Early Arthropod Evolution

[9981970]节肢动物在最近的发展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。节肢动物具有广泛的形态和生理特征，物种丰富，且化石记录可延伸至寒武纪，因此对多样性研究也应具有同等价值。然而，节肢动物多样性（从基因到形态）的研究由于缺乏明确可识别的单系类群而受到阻碍。因此，节肢动物进化史的许多基本方面仍然不确定。例如，在亚门中发现的与陆地化有关的形态学特征，如呼吸和运动的特征，是否代表了趋同或共享的衍生特征？对节肢动物关系的有力解决将代表历史生物学的重大进步，并将提供检验这些和许多其他进化假设的手段。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，证明甲壳类和六足类（称为pancrustae）是密切相关的，这与传统的六足类和多足类更密切相关的假设相反。结合我们对Chelicerata（包括Pycnogonida）和Myriapoda的单系性的有力支持，我们现在建议解决panrustaceae， Chelicerata和Myriapoda之间的基础节肢动物三分性。此外，我们建议解决在泛壳纲内的基本关系，特别是六足类相对于甲壳纲的位置；目前的分子（和形态学）证据不足以证明甲壳纲是单系动物。我们目前和计划中的系统发育研究利用从多个蛋白质编码、核基因序列中推断的核苷酸和氨基酸，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）。节肢动物及其近外类群54种，其中六足动物8种，甲壳动物23种，螯足动物6种，多足动物5种，缓步动物9种，爪足动物3种。已发表的形态学特征矩阵将根据我们强烈支持的分子结果重新分析。

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.