Relationships within Cornales and circumscription of Cornaceae-matK and rbcL sequence data and effects of outgroups and long branches

Phylogenetic relationships in Cornales were assessed using sequences rbcL and matK. Various combinations of outgroups were assessed for their suitability and the effects of long branches and outgroups on tree topology were examined using RASA 2.4 prior to conducting phylogenetic analyses. RASA identified several potentially problematic taxa having long branches in individual data sets that may have obscured phylogenetic signal, but when data sets were combined RASA no longer detected long branch problems. t(RASA) provides a more conservative measurement for phylogenetic signal than the PTP and skewness tests. The separate matK and rbcL sequence data sets were measured as not containing phylogenetic signal by RASA, but PTP and skewness tests suggested the reverse [corrected]. Nonetheless, the matK and rbcL sequence data sets suggested relationships within Cornales largely congruent with those suggested by the combined matK-rbcL sequence data set that contains significant phylogenetic signal as measured by t(RASA), PTP, and skewness tests. Our analyses also showed that a taxon having a long branch on the tree may not be identified as a "long-branched" taxon by RASA. The long branches identified by RASA had little effect on the arrangement of other taxa in the tree, but the placements of the long-branched taxa themselves were often problematic. Removing the long-branched taxa from analyses generally increased bootstrap support, often substantially. Use of non-optimal outgroups (as identified by RASA) decreased phylogenetic resolution in parsimony analyses and suggested different relationships in maximum likelihood analyses, although usually weakly supported clades (less than 50% support) were impacted. Our results do not recommend using t(RASA) as a sole criterion to discard data or taxa in phylogenetic analyses, but t(RASA) and the taxon variance ratio obtained from RASA may be useful as a guide for improved phylogenetic analyses. Results of parsimony and ML analyses of the sequence data using optimal outgroups suggested by RASA revealed four major clades within Cornales: (1) Curtisia-Grubbia, (2) Cornus-Alangium, (3) Nyssa-Camptotheca-Davidia-Mastixia-Diplopanax, and (4) Hydrangeaceae-Loasaceae, with clades (2) and (3) forming a monophyletic group sister to clade (4) and clade (1) sister to the remainder of Cornales. However, there was not strong bootstrap support for relationships among the major clades. The placement of Hydrostachys could not be reliably determined, although most analyses place the genus within Hydrangeaceae; ML analyses, for example, placed the genus as the sister of Hydrangeeae. Our results supported a Cornales including the systematically problematic Hydrostachys, a Cornaceae consisting of Cornus and Alangium, a Nyssaceae consisting of Nyssa and Camptotheca, a monogeneric Davidiaceae, a Mastixiaceae consisting of Mastixia and Diplopanax, and an expanded Grubbiaceae consisting of Grubbia and Curtisia, and two larger families, Hydrangeaceae and Loasaceae.     

从rbcL序列探讨单室茱萸属的系统位置

为了探讨单室茱萸属Mastixia的系统位置,本文对八蕊单室萸（Mastixia euony moides),云南单室茱萸（M.pentandra subsp,chinensis)及近缘物种云南紫树（Nyssa yunnanensis)和毛八角枫（Alangium kurzii)的cpDNA中编码1,5－二磷酸核酸糖羧化酶大亚基的rbcL基因序列进行了双脱氧测定。通过对这些序列与广义山茱萸科Cornaceae和Mastixia曾被归入的科的类群的rbcL序列进行PAUP（Phylogenetic Analysis Using Parsimony)分析,得到24棵最简约的分支树图。PAUP分析表明单室茱萸属与马蹄参属Diplopanax,紫树属Nyssa,喜树属Camptotheca和珙桐属Davidia的亲缘关系最近,并由分支图支持可以将Mastixia提升为山茱萸目Cornales中的一个科－单室萸科Masstixiaceae。     

Phylogenetic relationships of Cornaceae and close relatives inferred from matK and rbcL sequences

Phylogenetic relationships were inferred using nucleotide sequences of the chloroplast gene matK for members of Cornales, a well-supported monophyletic group comprising Cornaceae and close relatives. The shortest trees resulting from this analysis were highly concordant with those based on previous phylogenetic analysis of rbcL sequences. Analysis of a combined matK and rbcL sequence data set (a total of 2652 bp [base pairs]) provided greater resolution of relationships and higher internal support for clades compared to the individual data sets. Four major clades (most inclusive monophyletic groups) of Cornales are indicated by both sets of genes: (1) Cornus-Alangium, (2) nyssoids (Nyssa-Davidia-Camptotheca)- mastixioids (Mastixia, Diplopanax), (3) Curtisia, and (4) Hydrangeaceae-Loasaceae. The combined evidence indicates that clades 2 and 3 are sisters, with clade 4 sister to the remainder of Cornales. These relationships are also supported by other lines of evidence, including synapomorphies in fruit and pollen morphology and gynoecial vasculature. Comparisons of matK and rbcL sequences based on one of the most parsimonious rbcL-matK trees indicate that matK has a much higher A-T content (66.9% in matK vs. 55.8% in rbcL) and a lower transition:transversion ratio (1.23 in matK vs. 2.21 in rbcL). The total number of nucleotide substitutions per site for matK is 2.1 times that of rbcL in Cornales. These findings are similar to recent comparisons of matK and rbcL in other dicots. Variable sites of matK are almost evenly distributed among the three codon positions (1.0:1.0:1.3), whereas variable sites of rbcL are mostly at the third position (1.8:1.0 :7.5). Among- lineages rates of nucleotide substitutions in rbcL are basically homogeneous throughout Cornales, but are more heterogeneous in matK.     

Resolving and dating the phylogeny of Cornales--Effects of taxon sampling, data partitions, and fossil calibrations

The order Cornales descends from the earliest split in the Asterid clade of flowering plants. Despite a few phylogenetic studies, relationships among families within Cornales remain unclear. In the present study, we increased taxon and character sampling to further resolve the relationships and to date the early diversification events of the order. We conducted phylogenetic analyses of sequence data from 26S rDNA and six chloroplast DNA (cpDNA) regions using parsimony (MP), maximum likelihood (ML), and Bayesian inference (BI) methods with different partition models and different data sets. We employed relaxed, uncorrelated molecular clocks on BEAST to date the phylogeny and examined the effects of different taxon sampling, fossil calibration, and data partitions. Our results from ML and BI analyses of the combined cpDNA sequences and combined cpDNA and 26S rDNA data suggested the monophyly of each family and the following familial relationships ((Cornaceae-Alangiaceae)-(Curtisiaceae-Grubbiaceae))-(((Nyssaceae-Davidiaceae)-Mastixiaceae)-((Hydrostachyaceae-(Hydrangeaceae-Loasaceae))). These relationships were strongly supported by posterior probability and bootstrap values, except for the sister relationship between the N-D-M and H-H-L clades. The 26S rDNA data and some MP trees from cpDNA and total evidence suggested some alternative alignments for Hydrostachyaceae within Cornales, but results of SH tests indicated that these trees were significantly worse explanations of the total data. Phylogenetic dating with simultaneous calibration of multiple nodes suggested that the crown group of Cornales originated around the middle Cretaceous and rapidly radiated into several major clades. The origins of most families dated back to the late Cretaceous except for Curtisiaceae and Grubbiaceae which may have diverged in the very early Tertiary. We found that reducing sampling density within families and analyzing partitioned data sets from coding and noncoding cpDNA, 26S rDNA, and combined data sets produced congruent estimation of divergence times, but reducing the number and changing positions of calibration points resulted in very different estimations.     

Phylogenetic relationships of Loasaceae subfamily Gronovioideae inferred from matK and ITS sequence data

Members of subfamily Gronovioideae are distinctive among Loasaceae in their androecial and gynoecial simplicity. The four genera of the subfamily differ, however, in chromosome number, floral novelties, and pollen exine sculpturing, which led to suggestions that the Gronovioideae were polyphyletic. Phylogenetic analyses based on sequences of the chloroplast gene matK and the internal transcribed spacer region (ITS) of nuclear rDNA have been conducted using parsimony and maximum likelihood methods to assess the monophyly of Gronovioideae and to determine the sister group relationships of gronovioid genera. The results show Gronovioideae are monophyletic and placed as the sister to Mentzelia. Within Gronovioideae, Petalonyx is sister to a clade consisting of Cevallia, Gronovia, and Fuertesia. Among the remaining Loasaceae, subfamily Mentzelioideae, as originally circumscribed, is paraphyletic. Subfamily Loasoideae is placed as the sister to the Gronovioideae-Mentzelia clade.     

Sequences of 72 plastid genes support the early divergence of Cornales in the asterids

Recent phylogenetic analyses of molecular data have supported different hypotheses of relationships among Cornales,Ericales,and core asterids.Such hypotheses have implications for the evolution of important morphological and embryological features of asterids.In this study we generated plastid genome-scale data of Davidia (Cornales) and Franklinia (Ericales) and combined them with published sequence data of eudicots.Our maximum parsimony,maximum likelihood,and Bayesian analyses generated strongly supported and congruent phylogenetic relationships among the three major lineages of the asterids.Cornales diverges first in asterids; Ericales is sister to the core asterids.Adding two more taxa helps mitigate long branch attraction in parsimony analyses.Sampling 26-28 plastid protein-coding genes may provide satisfactory resolution and support for relationships of eudicots including basal lineages of asterids.     

基于28S rDNA D1-D2基因片段与16S rDNA部分序列联合分析的叶肢介系统发育研究

叶肢介(Conchostraca)的系统发育问题一直是甲壳动物研究中颇具争议的一个课题.本研究测定了我国2种叶肢介(Eocyzicus mongolianus,Eoc yzicus orientalis)的28S rDNA D1-D2区基因序列和16S rDNA E-G区序列,并与GenBank中的20种叶肢介序列一起...     

Phylogenetic inference regarding Parergodrilidae and Hrabeiella periglandulata ('Polychaeta', Annelida) based on 18S rDNA, 28S rDNA and COI sequences

Parergodrilidae and Hrabeiella periglandulata are Annelida showing different combinations of clitellate-like and aclitellate characters. Similarities between both of these taxa and Clitellata have widely been regarded as the result of convergent evolution due to similar selection pressures. The position of the three taxa in the phylogenetic system of Annelida is still in debate. However, in analyses based on 18S rDNA sequences a close relationship of Parergodrilidae with Orbiniidae and Questidae was suggested. To infer their phylogeny the sequences of the 28S rDNA and of the cytochrome oxidase I (COI) gene of Stygocapitella subterranea , Parergodrilus heideri and H. periglandulata were determined. The data were extended by sequences of various species including species from Clitellata and Orbiniidae. Prior to tree reconstruction the dataset was analysed in detail for phylogenetic content by applying a sliding window analysis, a likelihood mapping and Modeltest V.3.04. Subsequently, generalized parsimony and maximum likelihood methods were employed. Clade robustness was estimated by bootstrapping. In addition, combined analyses of the sequences of 18S rDNA and 28S rDNA as well as of 18S rDNA, 28S rDNA and COI were performed. The combination of the data of the two structure genes and a mitochondrial gene improved the resolution obtained with the single datasets slightly. These analyses support a close relationship of Parergodrilidae and Orbiniidae but cannot resolve the position of H. periglandulata . In every analysis Clitellata cluster within 'Polychaeta', confirming previous investigations.     

Phylogenetic study of Baylisascaris schroederi isolated from Qinling subspecies of giant panda in China based on combined nuclear 5.8S and the second internal transcribed spacer (ITS-2) ribosomal DNA sequences

The nuclear ribosomal DNA (rDNA) region spanning 5.8S rDNA and the second internal transcribed spacer (ITS-2) of Baylisascaris schroederi isolated from the Qinling subspecies of giant panda in Shaanxi Province, China were amplified and sequenced. Sequence variations in the two rDNA regions within B. schroederi and among species in the family Ascarididae were examined. The lengths of B. schroederi 5.8S and ITS-2 rDNA sequences were 156 bp and 327 bp, respectively, and no nucleotide variation was found in these two rDNA regions among the 20 B. schroederi samples examined, and these ITS-2 sequences were identical to that of B. schroederi isolated from giant panda in Sichuan province, China. The inter-species differences in 5.8S and ITS-2 rDNA sequences among members of the family Ascarididae were 0-1.3% and 0-17.7%, respectively. Phylogenetic relationships among species in the Ascarididae were re-constructed by Bayesian inference (Bayes), maximum parsimony (MP), and maximum likelihood (ML) analyses, based on combined sequences of 5.8S and ITS-2 rDNA. All B. schroederi samples clustered together and sistered to B. transfuga with high posterior probabilities/bootstrap values, which further confirmed that nematodes isolated from the Qinling subspecies of giant panda in Shaanxi Province, China represent B. schroederi. Because of the large number of ambiguously aligned sequence positions (difficulty of inferring homology by positions), ITS-2 sequence alone is likely unsuitable for phylogenetic analyses at the family level, but the combined 5.8S and ITS-2 rDNA sequences provide alternative genetic markers for the identification of B. schroederi and for phylogenetic analysis of parasites in the family Ascarididae.     

The phylogenetic potential of entire 26S rDNA sequences in plants

18S ribosomal RNA genes are the most widely used nuclear sequences for phylogeny reconstruction at higher taxonomic levels in plants. However, due to a conservative rate of evolution, 18S rDNA alone sometimes provides too few phylogenetically informative characters to resolve relationships adequately. Previous studies using partial sequences have suggested the potential of 26S or large-subunit (LSU) rDNA for phylogeny retrieval at taxonomic levels comparable to those investigated with 18S rDNA. Here we explore the patterns of molecular evolution of entire 26S rDNA sequences and their impact on phylogeny retrieval. We present a protocol for PCR amplification and sequencing of entire (approximately 3.4 kb) 26S rDNA sequences as single amplicons, as well as primers that can be used for amplification and sequencing. These primers proved useful in angiosperms and Gnetales and likely have broader applicability. With these protocols and primers, entire 26S rDNA sequences were generated for a diverse array of 15 seed plants, including basal eudicots, monocots, and higher eudicots, plus two representatives of Gnetales. Comparisons of sequence dissimilarity indicate that expansion segments (or divergence domains) evolve 6.4 to 10.2 times as fast as conserved core regions of 26S rDNA sequences in plants. Additional comparisons indicate that 26S rDNA evolves 1.6 to 2.2 times as fast as and provides 3.3 times as many phylogenetically informative characters as 18S rDNA; compared to the chloroplast gene rbcL, 26S rDNA evolves at 0.44 to 1.0 times its rate and provides 2.0 times as many phylogenetically informative characters. Expansion segment sequences analyzed here evolve 1.2 to 3.0 times faster than rbcL, providing 1.5 times the number of informative characters. Plant expansion segments have a pattern of evolution distinct from that found in animals, exhibiting less cryptic sequence simplicity, a lower frequency of insertion and deletion, and greater phylogenetic potential.      

A REASSESSMENT OF PHYLOGENETIC RELATIONSHIPS WITHIN THE PHAEOPHYCEAE BASED ON RUBISCO LARGE SUBUNIT AND RIBOSOMAL DNA SEQUENCES

To better assess the current state of phaeophycean phylogeny, we compiled all currently available rbc L, 18S, and 26S rDNA sequences from the EMBL/GenBank database and added 21 new rbc L sequences of our own. We then developed three new alignments designed to maximize taxon sampling while minimizing information loss due to partial sequences. Phylogenetic analyses were performed on separate and combined data sets (with and without taxa from the sister classes Tribophyceae and Phaeothamniophyceae as outgroups) using a variety of assumption sets, tree-drawing algorithms (parsimony, neighbor joining, and likelihood), and resampling methods (bootstrap, decay, jackknife). Partition homogeneity testing (PHT) by codon position within rbc L showed that all positions could be used despite mild third position saturation. PHT by gene and domain within rDNA showed that the 26S D1 and D2 regions do not enhance phylogenetic signal even when combined with the 18S. The rbc L and rDNA (excluding the 26S D1 and D2) could be combined under PHT. The topology of the combined tree was the same as that of the rbc L tree alone, but bootstrap support was consistently higher in the combined analysis, applied to more branches, and enabled the establishment of sister group relationships among six orders. Although the taxon sampling for the combination tree was lower ( n = 22) than for individual gene analyses ( n = 58 for rbc L and n = 59 for rDNA), results show that the Laminariales (previously reported) and Sphacelariales (new) are both paraphyletic. Choristocarpus tenellus (Kützing) Zanardini is the most basal phaeophyte and the Dictyotales the most basal order. In contrast, the Laminariales sensu stricto ( s.s. ) and Ectocarpales sensu lato ( s.l. ) are the most derived. For phylogenetic studies in the Phaeophyceae, rbc L has more resolving power than rDNA, though the reason for this is unclear based on the fact that both genes are highly conserved.     

PHYLOGENY OF LOBOCHARACIUM (CHLOROPHYCEAE) AND ALLIES: A STUDY OF 18S AND 26S rDNA DATA1

The phylogenetic affinities of Lobocharacium coloradoense were investigated by analysis of combined 18S and 26S rDNA data. Results from both parsimony and likelihood methods supported a close alliance among Lobocharacium, Characiosiphon, and Characiochloris. These three taxa formed a clade near the base of the “Dunaliella” group within the chlamydomonad lineage. Protosiphon, which exhibits a siphonous habit similar to Characiosiphon and Lobocharacium, was not resolved as a close ally of the latter two taxa. The Lobocharacium alliance was characterized by the presence of an attachment pad associated with the nonmotile vegetative stage and pyrenoids that possess cytoplasmic invaginations. The pyrenoid feature is an ultrastructural trait that has now been observed in five different chlorophycean lineages. The Lobocharacium–Characiosiphon–Characiochloris clade is not predicted by any classifications of green algae. Additional taxon and data sampling need to be completed to resolve inconsistencies between the molecular phylogenetic evidence and at least some of the current family‐level taxa.     

Evidence for host-specific clades of tetraphyllidean tapeworms (Platyhelminthes: Eucestoda) revealed by analysis of 18S ssrDNA

Sequence data from the V4 and V7-V9 variable regions of the 18S small subunit ribosomal DNA (ssrDNA) gene were used to examine relationships among 26 tetraphyllidean and two lecanicephalidean taxa. Newly collected specimens of 21 of the tetraphyllidean species were used to generate ssrDNA sequences that were combined with sequences previously available, including those of two diphyllidean taxa used for outgroup rooting. The sequences were aligned by eye according to secondary structural motifs of the conserved core of the molecule. Of the 1520 sites in the alignment, 874 (58%) were excluded from analysis due to alignment gaps and lack of positional homology as inferred by manual inspection. Genetic variability of the ssrDNA gene regions compared was greater than would be expected, based on the present taxonomy of the ingroup species, and the genetic divergences among tetraphyllidean 'families' and genera were comparable to that among tapeworm orders. Phylogenetic hypotheses were generated by the methods of maximum parsimony and maximum likelihood (GTR + I + Gamma nucleotide substitution model). Four most parsimonious trees resulted from analysis by maximum parsimony. Strict consensus of the four trees supported the monophyly of the Tetraphyllidea, with the lecanicephalidean taxa forming a sister lineage. Among the tetraphyllidean taxa included in the analysis were three major clades: a basal clade including species of the phyllobothriid genera Anthocephalum, Echeneibothrium, Rhinebothrium, Rhodobothrium and Spongiobothrium; a clade uniting the phyllobothriids of the genus Duplicibothrium with the dioecotaeniid genus Dioecotaenia; and a larger sister clade to the Duplicibothrium + Dioecotaenia clade that included the phyllobothriid genera Caulohothrium, Ceratobothrium, Clistobothrium, Paraoryigmatobothrium and Prosobothrium, the litobothriid genus Litobothrium and the onchobothriid genera Acanthobothrium, Calliobothrium, Phoreiobothrium and Platybothrium. Maximum likelihood analysis resulted in a topology that was congruent where nodes were strongly supported by parsimony analysis, but differed in the relative positions of the well-supported clades. In addition,maximum likelihood analysis grouped the lecanicephalidean taxa among the tetraphyllidean taxa, indicating paraphyly of the order Tetraphyllidea as currently defined. Relationships suggested by both methods of analysis reflected common host associations of the taxa better than their current classification, suggesting that coevolution has had a significant role in the evolution of the group.     

PHYLOGENY OF PHOTOSYNTHETIC EUGLENOPHYTES BASED ON COMBINED CHLOROPLAST AND CYTOPLASMIC SSU RDNA SEQUENCE ANALYSIS1

Eighteen new 16S rDNA and 16 new 18S rDNA sequences from 24 strains, representing 23 species of photoautotrophic euglenoids, were obtained in nearly their entire length. Maximum parsimony, maximum likelihood, and Bayesian phylogenetic analyses were performed on separate data (39 sequences of 16S rDNA and 58 sequences of 18S rDNA), as well as on combined data sets (37 sequences). All methods of sequence analysis gave similar results in those cases in which the clades received substantial support. However, the combined data set produced several additional well‐supported clades, not encountered before in the analyses of green euglenoids. There are three main well‐defined clades (A, B/C/D, and G) on trees from the combined data set. Clade G diverges first, while clades A and B/C/D form sister groups. Clade A consists of Euglena species sensu stricto and is divided into three sub‐clades (A1, A2, and A3). Clade A3 (composed of E. deses and E. mutabilis) branches off first; then, two sister clades emerge: A1 (composed of E. viridis‐like species) and A2 (consisting of E. agilis and E. gracilis species). Clade B/C/D consists of the Strombomonas, Trachelomonas, Cryptoglena, Monomorphina, and Colacium genera. Clade G comprises Phacus and Lepocinclis, as well as the Discoglena species of Euglena, with Discoglena branching off first, and then Phacus and Lepocinclis emerging as sister groups.     

基于5.8SrDNA序列论三白草科的系统发育

三白草科（Saururaceae)是古草本的一个核心类群,它的研究对被子植物起源和早期演化具有重要意义,本文采用最大简约法（maximum parsimony method)和邻接法（neighbor-joining method)等不同的分析方法,对三白草科及其外类群齐头绒（Zippelia begoniaefolia Blume)的5.85rDNA序列进行分析,得到一致的结论：Anemopsis最早从三白草科中分离出来,Saururus chinensis和S.cernuus是一对姐群,由于5.85rDNA序列的变异位点和信息位点相对比较少,Gymnotheca chinensis-G.involucrata-Houttuynia-Saururus之间难以通过5.8SrDNA序列的比较进行分辨。     

New insights into polychaete phylogeny (Annelida) inferred from 18S rDNA sequences

Annelid systematics and the ingroup relationships of polychaete annelids are matter of ongoing debates in recent analyses. For the investigation of sedentary polychaete relationships a molecular phylogenetic analysis was conducted based on 94 sequences of 18S rDNA, including unpublished sequences of 13 polychaete species. The data set was analyzed with maximum parsimony and maximum likelihood methods, as wells as Bayesian inference. As in previous molecular analyses the monophyly of many traditional polychaete families is confirmed. No evidence has been found for a possible monophyly of Canalipalpata or Scolecida. In all analyses a placement of the Echiura as a derived polychaete ingroup with a close relationship to the Capitellidae is confirmed. The orbiniids appear paraphyletic with regard to Questa. Travisia is transferred from Opheliidae to Scalibregmatidae. The remaining opheliids include a yet undescribed ctenodrilid species from Elba, whereas the other investigated ctenodrilid Ctenodrilus serratus groups with the Cirratulidae and shows a close affinity to the cirratulid genus Dodecaceria. A common ancestry of Branchiomaldane and Arenicola, which has been predicted on morphological data, is confirmed by the analysis and a sistergroup relationship between Arenicolidae and Maldanidae is also recovered. These results support our assumption that on the basis of a broader taxon sampling the phylogenetic position of controversially discussed taxa can be inferred by using 18S rDNA sequence data.     

A Phylogenetic Analysis of Heterorhabditis (Nemata: Rhabditidae) Based on Internal Transcribed Spacer 1 DNA Sequence Data

Internal transcribed spacer 1 sequences were used to infer phylogenetic relationships among 8 of the 9 described species and one putative species of the entomopathogenic nematode genus Heterorhabditis. Sequences were aligned and optimized based on pairwise genetic distance and parsimony criteria and subjected to a variety of sequence alignment parameters. Phylogenetic trees were constructed with maximum parsimony, cladistic, distance, and maximum likelihood algorithms. Our results gave strong support for four pairs of sister species, while relationships between these pairs also were resolved but less well supported. The ITS1 region of the nuclear ribosomal repeat was a reliable source of homologous characters for resolving relationships between closely related taxa but provided more tenuous resolution among more divergent lineages. A high degree of sequence identity and lack of autapomorphic characters suggest that sister species pairs within three distinct lineages may be mutually conspecific. Application of these molecular data and current morphological knowledge to the delimitation of species is hindered by an incomplete understanding of their variability in natural populations.     

速足目主要类群系统发育的分子证据

文章基于速足目现生主要类群18S rDNA、28S rDNA和COI基因序列,采用贝叶斯法、邻接法和最大简约法,尝试构建速足目的分子系统树;结合形态特征和化石记录,主要对速足目各超科级分类阶元的系统发育关系进行探讨。结果表明,速足目现生超科Bairdiacea、Darwinulacea、Cypridacea和Cytheracea均为单系群,支持形态学上关于上述4个超科的的界定;3种基因均支持形态学上Darwinulacea和Cypridacea具有较近的亲缘关系的观点。18S rDNA序列分析在较显著水平上支持Darwinulacea和Bairdiacea为姐妹群,Darwinulacea可能从Bairdia-cea中的一支演化而来;Bairdiacea和Darwinulacea组成的分支是Cypridacea的姐妹群,支持将三者合并为Bairdio-copina亚目的观点;Cytheracea是Cypridacea(Darwinulacea Bairdiacea)的姐妹群,可提升为Cytheracopina亚目。     

Phylogeny of Tunicata inferred from molecular and morphological characters

The phylogeny of the Tunicata was reconstructed using molecular and morphological characters. Mitochondrial cytochrome oxidase I (cox1) and 18S rDNA sequences were obtained for 14 and 4 tunicate species, respectively. 18S rDNA sequences were aligned with gene sequences obtained from GenBank of 57 tunicates, a cephalochordate, and a selachian craniate. Cox1 sequences were aligned with the sequence of two ascidians and a cephalochordate obtained from GenBank. Traditional, morphological, life history, and biochemical characters of larval and adult stages were compiled from the literature and analyzed cladistically. Separate and simultaneous parsimony analyses of molecular and morphological data were carried out. Aplousobranch ascidians from three different families were included in a molecular phylogenetic analysis for the first time. Analysis of the morphological, life history, and biochemical characters results in a highly unresolved tree. Aplousobranchiata form a strongly supported monophylum in the analysis of the 18S rDNA data, the morphological data, and the combined data set. Cionidae is not included in the Aplousobranchiata but nests within the Phlebobranchiata. Appendicularia (=Larvacea) nest within the 'Ascidiacea' as the sister taxon of Aplousobranchiata in the parsimony analysis of the 18S rDNA data and the combined analysis. A potential morphological synapomorphy of Aplousobranchiata plus Appendicularia is the horizontal orientation of the larval tail. In the 18S rDNA and the combined analysis, Thaliacea is included in the 'Ascidiacea' as the sister group to Phlebobranchiata. Pyrosomatida is found to be the sister taxon to the Salpidae in analyses of 18S rDNA and combined data, whereas the analysis of the morphological data recovers a sister group relationship between Doliolidae and Salpidae. Results of cox1 analyses are incongruent with both the 18S rDNA and the morphological phylogenies. Cox1 sequences may evolve too rapidly to resolve relationships of higher tunicate taxa. However, the cox1 data may be useful at lower taxonomic levels.