Phylogeny of Passerida (Aves: Passeriformes) based on nuclear and mitochondrial sequence data

Passerida is a monophyletic group of oscine passerines that includes almost 3500 species (about 36%) of all bird species in the world. The current understanding of higher-level relationships within Passerida is based on DNA-DNA hybridizations [C.G. Sibley, J.E. Ahlquist, Phylogeny and Classification of Birds, 1990, Yale University Press, New Haven, CT]. Our results are based on analyses of 3130 aligned nucleotide sequence data obtained from 48 ingroup and 13 outgroup genera. Three nuclear genes were sequenced: c-myc (498-510 bp), RAG-1 (930 bp), and myoglobin (693-722 bp), as well one mitochondrial gene; cytochrome b (879 bp). The data were analysed by parsimony, maximum-likelihood, and Bayesian inference. The African rockfowl and rockjumper are found to constitute the deepest branch within Passerida, but relationships among the other taxa are poorly resolved--only four major clades receive statistical support. One clade corresponds to Passeroidea of [C.G. Sibley, B.L. Monroe, Distribution and Taxonomy of Birds of the World, 1990, Yale University Press, New Haven, CT] and includes, e.g., flowerpeckers, sunbirds, accentors, weavers, estrilds, wagtails, finches, and sparrows. Starlings, mockingbirds, thrushes, Old World flycatchers, and dippers also group together in a clade corresponding to Muscicapoidea of Sibley and Monroe [op. cit.]. Monophyly of their Sylvioidea could not be corroborated--these taxa falls either into a clade with wrens, gnatcatchers, and nuthatches, or one with, e.g., warblers, bulbuls, babblers, and white-eyes. The tits, penduline tits, and waxwings belong to Passerida but have no close relatives among the taxa studied herein.     

A re-evaluation of basal phylogenetic relationships within trogons (Aves: Trogonidae) based on nuclear DNA sequences

The avian clade Trogonidae (trogons) consists of approximately 40 species distributed pantropically in the Neotropical, Afrotropical and Indomalayan zoogeographical regions. In this study, we evaluate the basal phylogenetic relationships within the trogons based on DNA sequences from three nuclear introns [myoglobin intron 2, β -fibrinogen intron 7 and glyceraldehydes-3-phosphodehydrogenase (G3PDH) intron 11]. In addition, previously published cytochrome b and 12S sequences were re-analysed and combined with the nuclear data set. The analysis of the three nuclear genes combined suggests a sister group relationship between the Afrotropical ( Apaloderma ) and Indomalayan ( Harpactes ) clades, whereas the Neotropical taxa ( Trogon , Pharomachrus , and Priotelus ) form an unresolved polytomy basal to these two groups. In addition, two of the three individual gene trees also support a sister group relationship between the Afrotropical and Indomalayan trogons. This is at odds with previously published studies based on mitochondrial sequence data and DNA–DNA hybridization. The third nuclear intron (G3PDH), however, suggests that the Afrotropical trogons are basal relative the other trogons. This was also suggested by the mitochondrial data set, as well as the analysis of the combined nuclear and mitochondrial data. Both of these conflicting hypotheses are supported by high posterior probabilities. An insertion in β -fibrinogen further supports a basal position of the Afrotropical clade. Analyses of the myoglobin intron with additional outgroups place the root differently and strongly support monophyly of each of the zoogeographical regions (including the Neotropics), and these three clades form a basal trichotomy. This suggests that that rooting is a serious problem in resolving basal phylogenetic relationships among the trogons.     

A phylogeny for the Cisticolidae (Aves: Passeriformes) based on nuclear and mitochondrial DNA sequence data, and a re-interpretation of an unique nest-building specialization

Based on some general similarities in feeding adaptations, a large number of Old World passerine birds were in the past lumped in one broad family, the Sylviidae. Recent molecular studies, starting with the DNA-DNA hybridization work by Sibley et al. [Sibley, C.G., Ahlquist, J.E., 1990. Phylogeny and Classification of Birds: A Study in Molecular Evolution, Yale University Press, New Haven, CT], have revealed that this group is in fact a paraphyletic assemblage, mainly in the superfamily Sylvioidea, and within this assemblage a distinct group (the Cisticolidae) can be identified around the genus Cisticola. In this study we try to define natural lineages within it, based on DNA sequence data from 35 ingroup taxa representing 12 putative genera. Both nuclear myoglobin intron II (630 bp in our study) and mitochondrial ND2 (1041 bp) genes were sequenced, and 1671 bp were aligned and subjected to parsimony, maximum likelihood and Bayesian analyses. The results strongly support the monophyly of a cisticolid clade, with the Malagasy warblers Neomixis constituting the deepest branch within the clade. Three major clades receive statistical support, but not all relationships between and within these are well resolved. All species of the genus Bathmocercus belong to the Cisticolidae but in two different clades. The tailorbirds appear also polyphyletic with most species of the genus Orthotomus (but O. cucullatus falling in the outgroup) and the African metopias being in two different clades. Also the genus Apalis is polyphyletic, but all other included genera seem to be confirmed as natural units. Based on these findings we resurrect the genera Scepomycter and Artisornis. Calamonastes is confirmed to be in the Cisticolidae and grouped with Camaroptera. Main basic nest types do not follow the phylogenetic branching, and notably the peculiar "tailorbird" technique of stitching leaves together around the nest is found in different parts of the phylogeny. The basic types of nests seem to be found in particular environments, and the sewing may therefore have evolved in some ancestor of the Cisticolidae and was later lost or modified in some genera or species following the spread of drier habitats from the mid-Miocene.     

Multilocus phylogeny of the widely distributed South American lizard clade Eulaemus (Liolaemini,Liolaemus)

The lizard genus Liolaemus and different clades within it have been the focus of several recent phylogenetic studies mainly based on morphology and mtDNA. Although there is general consensus for recognizing two clades (subgenera) within the genus, [Liolaemus (sensu stricto) and Eulaemus], phylogenetic relationships within each subgenus remain difficult to elucidate, given incomplete taxonomic sampling and large discordance between published studies. Here, new phylogenetic relationships for the Eulaemus subgenus are proposed based on the largest molecular data set ever used for this clade, which includes 188 individuals and 14 loci representing different parts of the genome (mtDNA, anonymous nuclear loci and nuclear protein‐coding loci). This data set was analysed using two species tree approaches (*beast and MDC). Levels of discordance among methods were found, and with previously published studies, but results are robust enough to propose new phylogenetic hypotheses for the Eulaemus clade. Specifically well‐resolved and well‐supported novel hypotheses are provided within the lineomaculatus section, and we formally recognize the zullyae clade, the sarmientoi clade and the hatcheri group. We also resolve species relationships within the montanus section, and particularly within the melanops series. We found discordance between mitochondrial and nuclear trees and discussed alternative hypotheses for the lineomaculatus and montanus sections, as well as the challenge in resolving phylogenetic relationships for large clades in general.     

Molecular evidence of Pleistocene bidirectional faunal exchange between Europe and the Near East: the case of the bicoloured shrew (Crocidura leucodon, Soricidae)

We sequenced 1077 bp of the mitochondrial cytochrome b gene and 511 bp of the nuclear Apolipoprotein B gene in bicoloured shrew (Crocidura leucodon, Soricidae) populations ranging from France to Georgia. The aims of the study were to identify the main genetic clades within this species and the influence of Pleistocene climatic variations on the respective clades. The mitochondrial analyses revealed a European clade distributed from France eastwards to north-western Turkey and a Near East clade distributed from Georgia to Romania; the two clades separated during the Middle Pleistocene. We clearly identified a population expansion after a bottleneck for the European clade based on mitochondrial and nuclear sequencing data; this expansion was not observed for the eastern clade. We hypothesize that the western population was confined to a small Italo-Balkanic refugium, whereas the eastern population subsisted in several refugia along the southern coast of the Black Sea.     

Nuclear and mitochondrial sequence data reveal the major lineages of starlings, mynas and related taxa

We investigated the phylogenetic relationships among the major lineages of the avian family Sturnidae and their placement within the Muscicapoidea clade using two nuclear (RAG-1 and myoglobin) and one mitochondrial gene (ND2). Among Muscicapoidea, we recovered three clades corresponding to the families Cinclidae, Muscicapidae and Sturnidae (sensu [Sibley, C.G., Monroe Jr., B.L., 1990. Distribution and Taxonomy of Birds of the World. Yale University Press, New Haven, CT]). Within the sturnoid lineage Mimini and Sturnini are sister groups, with Buphagus basal to them. We identified three major lineages of starlings: the Philippine endemic genus Rhabdornis, an Oriental-Australasian clade (genera Scissirostrum, Gracula, Mino, Ampeliceps, Sarcops, Aplonis), and an Afrotropical-Palaearctic clade (all African taxa, Sturnus and Acridotheres). We discuss the biogeographic implications of our findings and suggest an Asiatic origin for this family. The congruence between the age of major clades, estimated by NPRS, and palaeoclimatic data present evidence for the role of climatic changes in shaping present day distribution of the group.     

Testing morphology-based hypotheses of phylogenetic relationships in Parmeliaceae (Ascomycota) using three ribosomal markers and the nuclear RPB1 gene

Parmeliaceae is the largest family of lichen-forming fungi with more than 2000 species and includes taxa with different growth forms. Morphology was widely employed to distinguish groups within this large, cosmopolitan family. In this study we test these morphology-based groupings using DNA sequence data from three nuclear and one mitochondrial marker from 120 taxa that include 59 genera and represent the morphological and chemical diversity in this lineage. Parmeliaceae is strongly supported as monophyletic and six well-supported main clades can be distinguished within the family. The relationships among them remain unresolved. The clades largely agree with the morphology-based groupings and only the placement of four of the genera studied is rejected by molecular data, while four other genera belong to clades previously unrecognised. The classification of these previously misplaced genera, however, has already been questioned by some authors based on morphological evidence. These results support morphological characters as important for the identification of monophyletic clades within Parmeliaceae.     

Population structure of the Indonesian giant tiger shrimp Penaeus monodon: a window into evolutionary similarities between paralogous mitochondrial DNA sequences and their genomes

Here we used both microsatellites and mtCR (mitochondrial DNA control region) sequences as genetic markers to examine the genetic diversity and population structure of Penaeus monodon shrimp from six Indonesian regions. The microsatellite data showed that shrimp from the Indian and the Pacific Ocean were genetically distinct from each other. It has been reported previously that P. monodon mtCR sequences from the Indo‐Pacific group into two major paralogous clades of unclear origin. Here we show that the population structure inferred from mtCR sequences matches the microsatellite‐based population structure for one of these clades. This is consistent with the notion that this mtCR clade shares evolutionary history with nuclear DNA and may thus represent nuclear mitochondrial pseudogenes (Numts).     

Towards a better understanding of the higher systematics of Nymphalidae (Lepidoptera: Papilionoidea)

Research on the molecular systematics of higher taxa in the butterfly family Nymphalidae (Lepidoptera) is only just beginning. Outgroup selection is difficult at the moment due to the lack of consensus on the basal relationships of the major groups in Nymphalidae. We identify four major clades in the Nymphalidae based on a cladistic analysis of one mitochondrial gene sequence (COI, 1450 bp) and two nuclear gene sequences (EF-1alpha, 1064 bp, and wingless, 412-415 bp) from 54 exemplar species sampled from all currently recognized subfamilies. The COI data set was found to be highly incongruent with the nuclear data sets and a Partitioned Bremer Support analysis shows that the COI data set largely undermines support for most clades. Transitions at the third codon positions of the COI data set were highly saturated, but analyzing the combined data set with the COI third positions removed did not change the results. The major clades we found are termed the danaine clade (including Danainae), the satyrine clade (including Charaxinae, Satyrinae, Calinaginae, and Morphinae), the heliconiine clade (including Heliconiinae and Limenitidinae excluding Biblidini, Cyrestini, Pseudergolini, and Coeini) and the nymphaline clade (including Nymphalinae, Apaturinae, and Coeini, Cyrestini, Pseudergolini, and Biblidini from Limenitidinae). The heliconiine and nymphaline clades are sister groups, while the most parsimonious explanation for the combined data set places the danaine clade as the most basal large group of Nymphalidae. Our results give one of the strongest hypotheses for the subfamilial relationships within Nymphalidae. We were able to resolve the polyphyletic nature of Limenitidinae, which we recommend to be split into three subfamilies: Limenitidinae, Biblidinae, and Cyrestinae. The tribe Coeini belongs in Nymphalinae.     

Phylogenetic relationships of the African bush-shrikes and helmet-shrikes (Passeriformes: Malaconotidae)

The African bush-shrikes and helmet-shrikes (Malaconotidae sensu [A Complete Checklist of the Birds of the World, third ed., Helm Editions, London, 2003]) include 10 genera and 52 species of predatory passerine birds for which monophyly, sister-group, and inter-generic relationships are disputed. To resolve their relationships, we analyzed 2313 bp of sequence data obtained from two nuclear introns (myoglobin intron-2, beta-fibrinogen intron-5) and a mitochondrial protein-coding gene (ND2) using parsimony, maximum likelihood, and Bayesian inference. A strongly supported clade that included representatives of the Malaconotidae, Platysteiridae, and Vangidae was found in all analyses. Three main groups emerged within this clade but relationships between these three groups were always poorly supported. The first group included the helmet-shrikes (Prionops), flycatcher-shrikes (Bias and Megabyas), and vangas (Cyanolanius and Pseudobias), currently placed in the families Malaconotidae, Platysteiridae, and Vangidae, respectively. The second group consisted of four Platysteiridae genera (Lanioturdus, Batis, Platysteira, and Dyaphorophyia), with the remaining Malaconotidae genera ('core malaconotids') forming the last group. Two main clades emerged within the 'core malaconotids,' with the position of the genus Nilaus being variable. The first clade included Malaconotus, Dryoscopus, Bocagia, and Tchagra and the second Chlorophoneus, Laniarius, Rhodophoneus, and Telophorus. Monophyly of the genus Chlorophoneus was never recovered, a result that is consistent with morphological data.     

Phylogenetic relationships in the subgenus Mus (genus Mus, family Muridae, subfamily Murinae): examining gene trees and species trees

Over eight kilobases (kb) of sequence from eight genes including two mitochondrial loci, Cyt b and 12S, and six nuclear loci, B2m , Zp3 , Tcp1, Sry, Smcx and Smcy , were used to investigate phylogenetic relationships among 11 taxa representing eight species within the rodent genus Mus . Particular attention was given to discerning relationships among species within the subgenus Mus including members of a Palearctic clade ( M. musculus , M. spicilegus , M. macedonicus and M. spretus ) and members of an Asian clade ( M. caroli , M. cookii and M. cervicolor ), as previous studies using different datasets have produced different topologies for taxa within these two groups. While parsimony analyses of the combined eight-gene dataset yielded a single, fully resolved tree, support values were lower for nodes resolving relationships within the Palearctic and Asian clades than they were elsewhere in the tree. In addition, a maximum likelihood analysis of the same eight-gene dataset yielded different topologies for both the Palearctic and the Asian clades. Both observations are indicative of clade instability. The nature of this instability was explored through a comparison with our previous study in which we included the two mitochondrial loci and only four of the six nuclear genes, and through an analysis of partitioned data, specifically mitochondrial vs. nuclear genes. This study underscores the importance of considering among-site rate variation in phylogeny reconstruction. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 653–662.     

Mitochondrial and nuclear genes suggest that stony corals are monophyletic but most families of stony corals are not (Order Scleractinia, Class Anthozoa, Phylum Cnidaria)

Modern hard corals (Class Hexacorallia; Order Scleractinia) are widely studied because of their fundamental role in reef building and their superb fossil record extending back to the Triassic. Nevertheless, interpretations of their evolutionary relationships have been in flux for over a decade. Recent analyses undermine the legitimacy of traditional suborders, families and genera, and suggest that a non-skeletal sister clade (Order Corallimorpharia) might be imbedded within the stony corals. However, these studies either sampled a relatively limited array of taxa or assembled trees from heterogeneous data sets. Here we provide a more comprehensive analysis of Scleractinia (127 species, 75 genera, 17 families) and various outgroups, based on two mitochondrial genes (cytochrome oxidase I, cytochrome b), with analyses of nuclear genes (ss-tubulin, ribosomal DNA) of a subset of taxa to test unexpected relationships. Eleven of 16 families were found to be polyphyletic. Strikingly, over one third of all families as conventionally defined contain representatives from the highly divergent "robust" and "complex" clades. However, the recent suggestion that corallimorpharians are true corals that have lost their skeletons was not upheld. Relationships were supported not only by mitochondrial and nuclear genes, but also often by morphological characters which had been ignored or never noted previously. The concordance of molecular characters and more carefully examined morphological characters suggests a future of greater taxonomic stability, as well as the potential to trace the evolutionary history of this ecologically important group using fossils.     

Phylogeny and classification of the Old World Emberizini (Aves, Passeriformes)

The phylogeny of the avian genus Emberiza and the monotypic genera Latoucheornis, Melophus and Miliaria (collectively the Old World Emberizini), as well as representatives for the New World Emberizini, the circumpolar genera Calcarius and Plectrophenax and the four other generally recognized tribes in the subfamily Emberizinae was estimated based on the mitochondrial cytochrome b gene and introns 6-7 of the nuclear ornithine decarboxylase (ODC) gene. Our results support monophyly of the Old World Emberizini, but do not corroborate a sister relationship to the New World Emberizini. Calcarius and Plectrophenax form a clade separated from the other Emberizini. This agrees with previous studies, and we recommend the use of the name Calcariini. Latoucheornis, Melophus and Miliaria are nested within Emberiza, and we therefore propose they be synonymized with Emberiza. Emberiza is divided into four main clades, whose relative positions are uncertain, although a sister relation between a clade with six African species and one comprising the rest of the species (30, all Palearctic) is most likely. Most clades agree with traditional, morphology-based, classifications. However, four sister relationships within Emberiza, three of which involve the previously recognized Latoucheornis, Melophus and Miliaria, are unpredicted, and reveal cases of strong morphological divergence. In contrast, the plumage similarity between adult male Emberiza (formerly Latoucheornis) siemsseni and the nominate subspecies of the New World Junco hyemalis is shown to be the result of parallel evolution. A further case of parallel plumage evolution, between African and Eurasian taxa, is pointed out. Two cases of discordance between the mitochondrial and nuclear data with respect to branch lengths and genetic divergences are considered to be the result of introgressive hybridization.     

Phylogenetic relationships of the Dactyloa clade of Anolis lizards based on nuclear and mitochondrial DNA sequence data

The Dactyloa clade, one of two major subgroups of mainland Anolis lizards, is distributed from Costa Rica to Peru, including the Amazon region and the southern Lesser Antilles. We estimated the phylogenetic relationships within Dactyloa based on mitochondrial (ND2, five transfer-RNAs, COI) and nuclear (RAG1) gene regions using likelihood and Bayesian methods under different partition strategies. In addition, we tested the monophyly of five previously recognized groups within Dactyloa. The data strongly support the monophyly of Dactyloa and five major clades: eastern, latifrons, Phenacosaurus, roquet and western, each of which exhibits a coherent geographic range. Relationships among the five major clades are less clear: support for basal nodes within Dactyloa is weak and some contradictory relationships are supported by different datasets and/or phylogenetic methods. Of the previously recognized subgroups within Dactyloa, only the roquet series consistently passed the topology tests applied. The monophyly of the aequatorialis, latifrons (as traditionally circumscribed) and punctatus series was strongly rejected, and the monophyly of Phenacosaurus (as traditionally circumscribed) yielded mixed results. The results of the phylogenetic analyses suggest the need for a revised taxonomy and have implications for the biogeography and tempo of the Dactyloa radiation.     

Genetic differentiation of the pine processionary moth at the southern edge of its range: contrasting patterns between mitochondrial and nuclear markers

The pine processionary moth (Thaumetopoea pityocampa) is an important pest of coniferous forests at the southern edge of its range in Maghreb. Based on mitochondrial markers, a strong genetic differentiation was previously found in this species between western (pityocampa clade) and eastern Maghreb populations (ENA clade), with the contact zone between the clades located in Algeria. We focused on the moth range in Algeria, using both mitochondrial (a 648 bp fragment of the tRNA‐cox2) and nuclear (11 microsatellite loci) markers. A further analysis using a shorter mtDNA fragment and the same microsatellite loci was carried out on a transect in the contact zone between the mitochondrial clades. Mitochondrial diversity showed a strong geographical structure and a well‐defined contact zone between the two clades. In particular, in the pityocampa clade, two inner subclades were found whereas ENA did not show any further structure. Microsatellite analysis outlined a different pattern of differentiation, with two main groups not overlapping with the mitochondrial clades. The inconsistency between mitochondrial and nuclear markers is probably explained by sex‐biased dispersal and recent afforestation efforts that have bridged isolated populations.     

Species status and phylogeography of two closely related Coptolabrus species (Coleoptera: Carabidae) in South Korea inferred from mitochondrial and nuclear gene sequences

We investigated the species status and intraspecific phylogeography in South Korea of two ground beetle species, Coptolabrus jankowskii and Coptolabrus smaragdinus (Coleoptera: Carabidae), using statistical parsimony networks and nested clade analyses based on sequences from the mitochondrial cytochrome oxidase subunit I (COI) and nuclear phosphoenolpyruvate carboxykinase (PepCK) and wingless (Wg) genes. Although traditional parsimony tree construction generally failed to resolve interspecific relationships and construct biologically meaningful genealogies, analysis using statistical parsimony networks yielded statistically significant inter- and intraspecific genealogical structures. We found that although these two species represent a notable case of trans-species polymorphisms in both mitochondrial and nuclear gene sequences, their status as separate species was evidenced by the nonrandom association between species and nested clades at various nesting levels. The exceptional occurrence of shared identical or very similar COI sequences was considered to be the result of introgressive hybridization. In addition, range expansion and fragmentation events across the Korean Peninsula and adjacent islands were inferred from nested clade phylogeographical analyses. The COI gene revealed the geographical divergence of major eastern and western clades and historical biogeographical events within each major clade, whereas the nuclear PepCK gene, which did not reveal corresponding east-west clades, indicated past fragmentation and range expansion across wide areas that may have been the result of older biogeographical events. Thus, phylogeographical inferences drawn from analyses of mitochondrial and nuclear genes can reveal different and potentially complementary information about phylogeographical processes.     

A trend of central versus peripheral structuring in mitochondrial and nuclear gene sequences of the Japanese wood mouse, Apodemus speciosus

A phylogeographic analysis was performed on Japanese endemic wood mice (Apodemus speciosus) using nuclear interphotoreceptor retinol binding protein (IRBP) gene sequences (1,152 bp), together with previously published mitochondrial cytochrome b (cyt b) data. In the IRBP analysis, 40 haplotypes were recovered from 84 individuals by statistical and subcloning methods. Substantial sequence variation was determined from the IRBP data (pi=0.0047), and no significant evidence of recombination was detected. From the phylogenetic analysis, the 40 haplotypes fell into two major groups with geographic associations, irrespective of the karyotype groups (2n=46 and 2n=48), yielding a trend of central (Hokkaido, Honshu, Shikoku, Kyushu, and Sado) and peripheral (Izu, Oki, Tsushima, and Satsunan Is.) groupings. This geographic pattern is similar to that observed in the cyt b data, with a different insular grouping of Sado, Hokkaido, Izu, and Satsunan islands, and also to that of morphological features. In both gene data sets, nested clade analyses revealed allopatric fragmentation in the "peripheral island clades" and range expansion in the "central island clades." A mismatch analysis using cyt b data also suggested expansion of the central islands clade. Thus, the trend of central vs. peripheral structuring may be attributable to past demographic dynamics in the two distinct haplotype clades, such as range expansion of one clade in the central area of the Japanese Islands, leaving the other clade in the periphery.     

Monophyly of clade III nematodes is not supported by phylogenetic analysis of complete mitochondrial genome sequences

Background

The orders Ascaridida, Oxyurida, and Spirurida represent major components of zooparasitic nematode diversity, including many species of veterinary and medical importance. Phylum-wide nematode phylogenetic hypotheses have mainly been based on nuclear rDNA sequences, but more recently complete mitochondrial (mtDNA) gene sequences have provided another source of molecular information to evaluate relationships. Although there is much agreement between nuclear rDNA and mtDNA phylogenies, relationships among certain major clades are different. In this study we report that mtDNA sequences do not support the monophyly of Ascaridida, Oxyurida and Spirurida (clade III) in contrast to results for nuclear rDNA. Results from mtDNA genomes show promise as an additional independently evolving genome for developing phylogenetic hypotheses for nematodes, although substantially increased taxon sampling is needed for enhanced comparative value with nuclear rDNA. Ultimately, topological incongruence (and congruence) between nuclear rDNA and mtDNA phylogenetic hypotheses will need to be tested relative to additional independent loci that provide appropriate levels of resolution.

Results

For this comparative phylogenetic study, we determined the complete mitochondrial genome sequences of three nematode species, Cucullanus robustus (13,972 bp) representing Ascaridida, Wellcomia siamensis (14,128 bp) representing Oxyurida, and Heliconema longissimum (13,610 bp) representing Spirurida. These new sequences were used along with 33 published nematode mitochondrial genomes to investigate phylogenetic relationships among chromadorean orders. Phylogenetic analyses of both nucleotide and amino acid sequence datasets support the hypothesis that Ascaridida is nested within Rhabditida. The position of Oxyurida within Chromadorea varies among analyses; in most analyses this order is sister to the Ascaridida plus Rhabditida clade, with representative Spirurida forming a distinct clade, however, in one case Oxyurida is sister to Spirurida. Ascaridida, Oxyurida, and Spirurida (the sampled clade III taxa) do not form a monophyletic group based on complete mitochondrial DNA sequences. Tree topology tests revealed that constraining clade III taxa to be monophyletic, given the mtDNA datasets analyzed, was a significantly worse result.

Conclusion

The phylogenetic hypotheses from comparative analysis of the complete mitochondrial genome data (analysis of nucleotide and amino acid datasets, and nucleotide data excluding 3^rd positions) indicates that nematodes representing Ascaridida, Oxyurida and Spirurida do not share an exclusive most recent common ancestor, in contrast to published results based on nuclear ribosomal DNA. Overall, mtDNA genome data provides reliable support for nematode relationships that often corroborates findings based on nuclear rDNA. It is anticipated that additional taxonomic sampling will provide a wealth of information on mitochondrial genome evolution and sequence data for developing phylogenetic hypotheses for the phylum Nematoda.