Pepato A R, Klimov P B
Departamento de Zoologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Av. Antonio Carlos, 6627, 31270-901, Belo Horizonte, Brazil.
Department of Ecology and Evolutionary Biology, University of Michigan, 1109 Geddes Ave, Ann Arbor, MI, 48109-1079, USA.
BMC Evol Biol. 2015 Sep 2;15:178. doi: 10.1186/s12862-015-0458-2.
Acariformes is the most species-rich and morphologically diverse radiation of chelicerate arthropods, known from the oldest terrestrial ecosystems. It is also a key lineage in understanding the evolution of this group, with the most vexing question whether mites, or Acari (Parasitiformes and Acariformes) is monophyletic. Previous molecular studies recovered Acari either as monophyletic or non-monophyletic, albeit with a limited taxon sampling. Similarly, relationships between basal acariform groups (include little-known, deep-soil 'endeostigmatan' mites) and major lineages of Acariformes (Sarcoptiformes, Prostigmata) are virtually unknown. We infer phylogeny of chelicerate arthropods, using a large and representative dataset, comprising all main in- and outgroups (228 taxa). Basal diversity of Acariformes is particularly well sampled. With this dataset, we conduct a series of phylogenetically explicit tests of chelicerate and acariform relationships and present a phylogenetic framework for internal relationships of acariform mites.
Our molecular data strongly support a diphyletic Acari, with Acariformes as the sister group to Solifugae (PP =1.0; BP = 100), the so called Poecilophysidea. Among Acariformes, some representatives of the basal group Endeostigmata (mainly deep-soil mites) were recovered as sister-groups to the remaining Acariformes (i. e., Trombidiformes + and most of Sarcoptiformes). Desmonomatan oribatid mites (soil and litter mites) were recovered as the monophyletic sister group of Astigmata (e. g., stored product mites, house dust mites, mange mites, feather and fur mites). Trombidiformes (Sphaerolichida + Prostigmata) is strongly supported (PP =1.0; BP = 98-100). Labidostommatina was inferred as the basal lineage of Prostigmata. Eleutherengona (e. g., spider mites) and Parasitengona (e. g., chiggers, fresh water mites) were recovered as monophyletic. By contrast, Eupodina (e. g., snout mites and relatives) was not. Marine mites (Halacaridae) were traditionally regarded as the sister-group to Bdelloidea (Eupodina), but our analyses show their close relationships to Parasitengona.
Non-trivial relationships recovered by our analyses with high support (i.e., basal arrangement of endeostigmatid lineages, the position of marine mites, polyphyly of Eupodina) had been proposed by previous underappreciated morphological studies. Thus, we update currently the accepted taxonomic classification to reflect these results: the superfamily Halacaroidea Murray, 1877 is moved from the infraorder Eupodina Krantz, 1978 to Anystina van der Hammen, 1972; and the subfamily Erythracarinae Oudemans, 1936 (formerly in Anystidae Oudemans, 1902) is elevated to family rank, Erythracaridae stat. ressur., leaving Anystidae only with the nominal subfamily. Our study also shows that a clade comprising early derivative Endeostigmata (Alycidae, Nanorchestidae, Nematalycidae, and maybe Alicorhagiidae) should be treated as a taxon with the same rank as Sarcoptiformes and Trombidiformes, and the scope of the superfamily Bdelloidea should be changed. Before turning those findings into nomenclatural changes, however, we consider that our study calls for (i) finding shared apomorphies of the early derivative Endeostigmata clade and the clade including the remaining Acariformes; (ii) a well-supported hypothesis for Alicorhagiidae placement; (iii) sampling the families Proterorhagiidae, Proteonematalycidae and Grandjeanicidae not yet included in molecular analyses; (iv) undertake a denser sampling of clades traditionally placed in Eupodina, Anystina (Trombidiformes) and Palaeosomata (Sarcoptiformes), since consensus networks and Internode certainty (IC) and IC All (ICA) indices indicate high levels of conflict in these tree regions. Our study shows that regions of ambiguous alignment may provide useful phylogenetic signal when secondary structure information is used to guide the alignment procedure and provides an R implementation to the Bayesian Relative Rates test.
疥螨目是螯肢亚门节肢动物中物种最为丰富、形态最为多样的一个类群，最早见于陆地生态系统。它也是理解该类群进化的关键谱系，最令人困扰的问题是螨类，即蜱螨亚纲（寄螨目和疥螨目）是否为单系类群。以往的分子研究得出蜱螨亚纲要么是单系类群，要么不是单系类群，尽管分类单元的抽样有限。同样，基部疥螨目类群（包括鲜为人知的深层土壤“内气门亚目”螨类）与疥螨目主要谱系（真螨目、前气门亚目）之间的关系实际上尚不清楚。我们利用一个大型且具代表性的数据集推断螯肢亚门节肢动物的系统发育，该数据集包含所有主要的内群和外群（228个分类单元）。疥螨目的基部多样性得到了特别好的抽样。利用这个数据集，我们对螯肢亚门和疥螨目的关系进行了一系列系统发育明确的检验，并提出了一个疥螨目螨类内部关系的系统发育框架。
我们的分子数据有力地支持蜱螨亚纲为并系类群，疥螨目是避日蛛目的姐妹群（后验概率 = 1.0；自展支持率 = 100），即所谓的Poecilophysidea。在疥螨目中，基部类群内气门亚目的一些代表类群（主要是深层土壤螨类）被发现是其余疥螨目（即恙螨目 + 和大部分真螨目）的姐妹群。革螨目甲螨（土壤和凋落物螨类）被发现是粉螨亚目（如仓储螨类、屋尘螨、疥螨、羽螨和皮螨）的单系姐妹群。恙螨目（球螨亚目 + 前气门亚目）得到了有力支持（后验概率 = 1.0；自展支持率 = 98 - 100）。Labidostommatina被推断为前气门亚目的基部谱系。游殖螨类（如叶螨）和寄生螨类（如恙螨、淡水螨）被发现是单系类群。相比之下，真足螨类（如鼻螨及其近缘类群）则不是。海洋螨类（海螨科）传统上被认为是球螨总科（真足螨类）的姐妹群，但我们的分析表明它们与寄生螨类关系密切。
我们的分析以高支持率得出的重要关系（即内气门亚目谱系的基部排列、海洋螨类的位置、真足螨类的多系性）在之前未得到充分重视的形态学研究中已有提出。因此，我们目前更新公认的分类学分类以反映这些结果：1877年的海螨总科Murray从1978年的真足螨下目Krantz移至1972年的异气门螨下目van der Hammen；1936年的赤螨亚科Oudemans（原在1902年的异气门螨科Oudemans中）提升为科级，即赤螨科，新组合，使得异气门螨科仅保留名义亚科。我们的研究还表明，一个包含早期分化的内气门亚目（爱丽螨科、纳米甲螨科、线虫甲螨科，可能还有异角甲螨科）的分支应被视为与真螨目和恙螨目具有相同等级的一个分类单元，并且球螨总科的范围应有所改变。然而，在将这些发现转化为命名变化之前，我们认为我们的研究需要（i）找到早期分化的内气门亚目分支和包括其余疥螨目在内的分支的共同衍征；（ii）一个关于异角甲螨科位置的得到充分支持的假说；（iii）对尚未纳入分子分析的原角甲螨科、原线虫甲螨科和格兰甲螨科进行抽样；（iv）对传统上置于真足螨类、异气门螨类（恙螨目）和古螨类（真螨目）的类群进行更密集的抽样，因为共识网络以及节点确定性（IC）和全节点确定性（ICA）指数表明这些树状区域存在高度冲突。我们的研究表明，当利用二级结构信息指导比对过程时，比对不明确的区域可能会提供有用的系统发育信号，并提供了贝叶斯相对速率检验的R实现。
