Resolving arthropod phylogeny: exploring phylogenetic signal within 41 kb of protein-coding nuclear gene sequence

Development and morphology of podocopan ostracod limbs (Crustacea) - A review

Ostracods are tiny bivalved crustaceans, which have colonised almost all aquatic ecosystems. Their extensive fossil record, stretching back to the Ordovician, attests to their remarkable success, in part due to their calcitic carapace - a hard bivalved shell that can enclose the rest of the body for protection against unfavourable environmental conditions. However, the carapace, and the requirement for the limbs to fit within it, has resulted in a reduced number of limbs, which in turn show evidence of reduction from a biramous crustacean limb. Consequently, ostracod limbs are characterized by limited features and homoeomorphy, hindering our understanding of their evolution. Studies of ontogenetic development can offer additional insights into how ostracod limbs have evolved. For instance, there are at least four developmental pathways to a seven-segmented antennule in adults, which is significant for taxonomic classifications and phylogenetic analyses. Ontogenetic data can also identify possible plesiomorphic and apomorphic characters for the group, thereby testing phylogenetic and taxonomic frameworks. This review focuses on the Podocopa, the largest of the two extant subclasses, and explores how studying limb development during ontogeny can provide insights into the evolution of the group.

Arthropod Phylotranscriptomics With a Special Focus on the Basal Phylogeny of the Myriapoda

Arthropoda represents the most diverse animal phylum, but clarifying the phylogenetic relationships among arthropod taxa remains challenging given the numerous arthropod lineages that diverged over a short period of time. In order to resolve the most controversial aspects of deep arthropod phylogeny, focusing on the Myriapoda, we conducted phylogenetic analyses based on ten super-matrices comprised of 751 to 1,233 orthologous genes across 64 representative arthropod species, including 28 transcriptomes that were newly generated in this study. Our findings provide unambiguous support for the monophyly of the higher arthropod taxa, Chelicerata, Mandibulata, Myriapoda, Pancrustacea, and Hexapoda, while the Crustacea are paraphyletic, with the class Remipedia supported as the lineage most closely related to hexapods. Within the Hexapoda, our results largely affirm previously proposed phylogenetic relationships among deep hexapod lineages, except that the Paraneoptera (Hemiptera, Thysanoptera, and Psocodea) was recovered as a monophyletic lineage in some analyses. The results corroborated the recently proposed phylogenetic framework of the four myriapod classes, wherein Symphyla and Pauropoda, as well as Chilopoda and Diplopoda, are each proposed to be sister taxa. The findings provide important insights into understanding the phylogeny and evolution of arthropods.

Dataset from RNAseq analysis of differential gene expression among developmental stages of two non-marine ostracodes

We contribute transcriptomic data for two species of Ostracoda, an early-diverged group of small-sized pancrustaceans. Data include new reference transcriptomes for two asexual non-marine species (Dolerocypris sinensis and Heterocypris aff. salina), as well as single-specimen transcriptomic data that served to analyse gene expression across four developmental stages in D. sinensis. Data are evaluated by computing gene expression profiles of the different developmental stages which consistently placed eggs and small larvae (at the stage of instar A-8) similar to each other, and apart from adults which were distinct from all other developmental stages but closest to large larvae (instar A-4). We further evaluated the transcriptomic data with two newly sequenced low-coverage genomes of the target species. The new data thus document the feasibility of obtaining reliable transcriptomic data from single specimens - even eggs - of these small metazoans.

Genome-scale approach to reconstructing the phylogenetic tree of psyllids (superfamily Psylloidea) with account of systematic bias

Psyllids (class Insecta: order Hemiptera: superfamily Psylloidea) are a taxonomically and phylogenetically challenging clade. Recent studies have largely advanced the phylogeny of this group, yet the family-level relationships among Aphalaridae, Carsidaridae, and others remain unresolved. Genome-scale phylogenetic analysis is known to provide a finer resolution for problems like that. However, such phylogenomics also introduces new problems: incorrect trees with high confidence yielded due to systematic error (bias). Here we addressed these issues using hundreds of single-copy orthologous (SCO) genes in psyllid transcriptomes and genomes. Our analyses revealed conflicts between the nucleotide-based and amino-acid-based phylogenetic trees. While the nucleotide-based phylogeny strongly supported the (Aphalaridae + Carsidaridae) + Others relationship, the amino-acid-based one recovered Aphalaridae + (Carsidaridae + Others) with 100% support. Further inspection revealed significant compositional heterogeneity in nucleotide sequences for 67% of SCO genes, but not in the corresponding translated amino acid sequences. We then used different strategies to combat this compositional bias, and found that using the RY-coding strategy (coding the standard nucleotides as purines and pyrimidines) the nucleotide-based phylogeny became consistent with the amino-acid-based one. We further applied RY-coding to a published concatenated nucleotide dataset and recovered the Aphalaridae monophyly (which is refuted by the original literature on non-recoded sequences) at the base of psyllid tree. Moreover, it was found that variations in evolutionary rate could lead to errors in nucleotide-based phylogeny. The fast-evolving Heteropsylla cubana (Psyllidae: Ciriacreminae) was incorrectly placed within the subfamily Psyllinae. This bias can be avoided by using data removal or RY-coding strategies. Together, our results strongly support the family relationship of Aphalaridae + (Carsidaridae + Others), and show that the amino-acid-based concatenation analysis is more robust than nucleotide-based one. Future phylogenomic analysis of psyllid nucleotide sequences should take into account methods such as the RY-coding scheme to address potential systematic biases arising from composition and rate heterogeneities.

Major Revisions in Pancrustacean Phylogeny and Evidence of Sensitivity to Taxon Sampling

The clade Pancrustacea, comprising crustaceans and hexapods, is the most diverse group of animals on earth, containing over 80% of animal species and half of animal biomass. It has been the subject of several recent phylogenomic analyses, yet relationships within Pancrustacea show a notable lack of stability. Here, the phylogeny is estimated with expanded taxon sampling, particularly of malacostracans. We show small changes in taxon sampling have large impacts on phylogenetic estimation. By analyzing identical orthologs between two slightly different taxon sets, we show that the differences in the resulting topologies are due primarily to the effects of taxon sampling on the phylogenetic reconstruction method. We compare trees resulting from our phylogenomic analyses with those from the literature to explore the large tree space of pancrustacean phylogenetic hypotheses and find that statistical topology tests reject the previously published trees in favor of the maximum likelihood trees produced here. Our results reject several clades including Caridoida, Eucarida, Multicrustacea, Vericrustacea, and Syncarida. Notably, we find Copepoda nested within Allotriocarida with high support and recover a novel relationship between decapods, euphausiids, and syncarids that we refer to as the Syneucarida. With denser taxon sampling, we find Stomatopoda sister to this latter clade, which we collectively name Stomatocarida, dividing Malacostraca into three clades: Leptostraca, Peracarida, and Stomatocarida. A new Bayesian divergence time estimation is conducted using 13 vetted fossils. We review our results in the context of other pancrustacean phylogenetic hypotheses and highlight 15 key taxa to sample in future studies.

Revision of the African Neoperla Needham, 1905 (Plecoptera: Perlidae: Perlinae) based on morphological and molecular data

Adults of the African species of the genus Neoperla Needham, 1905 (Plecoptera: Perlidae: Perlinae) are revised, and 82 valid species are recognised. Of the original 29 named species, 14 valid ones are redescribed from types, nine lectotypes are designated, and nine new synonymies are proposed. Sixty-two new species are named, and several additional new species only known from material insufficient for formal description are listed. There are one unavailable nomen nudum and three doubtful names. Diagnostic morphological traits of the recognised species are described and illustrated in detail where available of males, females, and eggs. Dichotomous keys to all species are provided. Mitochondrial DNA-data of 71 species-group taxa are available, which permits reliable association of sexes and minimises the risk of synonymies between species known from only one sex. Importantly, this includes DNA sequences from 50 holotypes. The DNA-data will also permit future monitoring with eDNA sequencing and identification of nymphs, which are probably important but so far unidentifiable bioindicators in streams. The genus Neoperla occurs largely in the northern hemisphere and in Africa, where it is restricted to the Ethiopian region south of the Sahara but unknown from Madagascar. A single specimen not clearly distinct from a widespread mainland species was taken on Comoro Island. All African species are endemic, but one African species group has a few outlying members in Asia. The Asian N. montivaga-group is not known from Africa. The following new species are described and named: N. aethiopica n. sp., N. amoena n. sp., N. angolana n. sp., N. bareensis n. sp., N. bella n. sp., N. benti n. sp., N. beta n. sp., N. bipolaris n. sp., N. biserrata n. sp., N. brachyphallus n. sp., N. caeleps n. sp., N. cataractae n. sp., N. claviger n. sp., N. coffea n. sp., N. costata n. sp., N. crenulata n. sp., N. crustata n. sp., N. decorata n. sp., N. dianae n. sp., N. dolium n. sp., N. dundoana n. sp., N. duodeviginti n. sp., N. erinaceus n. sp., N. excavata n. sp., N. filamentosa n. sp., N. funiculata n. sp., N. gibbosa n. sp., N. gordius n. sp., N. heideae n. sp., N. ivanloebli n. sp., N. juxtadidita n. sp., N. kalengonis n. sp., N. larvata n. sp., N. lineata n. sp., N. luhohonis n. sp., N. massevensis n. sp., N. multiserrata n. sp., N. muyukae n. sp., N. nichollsi n. sp., N. occulta n. sp., N. orthonema n. sp., N. pallidogigas n. sp., N. panafricana n. sp., N. pickeri n. sp., N. pilulifera n. sp., N. pirus n. sp., N. planidorsum n. sp., N. plicata n. sp., N. proxima n. sp., N. pusilla n. sp., N. rostrata n. sp., N. sambarua n. sp., N. sassandrae n. sp., N. schuelei n. sp., N. serrula n. sp., N. simplex n. sp., N. socia n. sp., N. sorella n. sp., N. spaghetti n. sp., N. spectabilis n. sp., N. spironema n. sp., N. tangana n. sp., N. tansanica n. sp., N. usambara n. sp., and N. vicina n. sp..

Untying the Gordian knot of plastid phylogenomic conflict: A case from ferns

Phylogenomic studies based on plastid genome have resolved recalcitrant relationships among various plants, yet the phylogeny of Dennstaedtiaceae at the level of family and genera remains unresolved due to conflicting plastid genes, limited molecular data and incomplete taxon sampling of previous studies. The present study generated 30 new plastid genomes of Dennstaedtiaceae (9 genera, 29 species), which were combined with 42 publicly available plastid genomes (including 24 families, 27 genera, 42 species) to explore the evolution of Dennstaedtiaceae. In order to minimize the impact of systematic errors on the resolution of phylogenetic inference, we applied six strategies to generate 30 datasets based on CDS, intergenic spacers, and whole plastome, and two tree inference methods (maximum-likelihood, ML; and multispecies coalescent, MSC) to comprehensively analyze the plastome-scale data. Besides, the phylogenetic signal among all loci was quantified for controversial nodes using ML framework, and different topologies hypotheses among all datasets were tested. The species trees based on different datasets and methods revealed obvious conflicts at the base of the polypody ferns. The topology of the "CDS-codon-align-rm3" (CDS with the removal of the third codon) matrix was selected as the primary reference or summary tree. The final phylogenetic tree supported Dennstaedtiaceae as the sister group to eupolypods, and Dennstaedtioideae was divided into four clades with full support. This robust reconstructed phylogenetic backbone establishes a framework for future studies on Dennstaedtiaceae classification, evolution and diversification. The present study suggests considering plastid phylogenomic conflict when using plastid genomes. From our results, reducing saturated genes or sites can effectively mitigate tree conflicts for distantly related taxa. Moreover, phylogenetic trees based on amino acid sequences can be used as a comparison to verify the confidence of nucleotide-based trees.

A Rearrangement of the Mitochondrial Genes of Centipedes (Arthropoda, Myriapoda) with a Phylogenetic Analysis

Due to the limitations of taxon sampling and differences in results from the available data, the phylogenetic relationships of the Myriapoda remain contentious. Therefore, we try to reconstruct and analyze the phylogenetic relationships within the Myriapoda by examining mitochondrial genomes (the mitogenome). In this study, typical circular mitogenomes of Mecistocephalus marmoratus and Scolopendra subspinipes were sequenced by Sanger sequencing; they were 15,279 bp and 14,637 bp in length, respectively, and a control region and 37 typical mitochondrial genes were annotated in the sequences. The results showed that all 13 PCGs started with ATN codons and ended with TAR codons or a single T; what is interesting is that the gene orders of M. marmoratus have been extensively rearranged compared with most Myriapoda. Thus, we propose a simple duplication/loss model to explain the extensively rearranged genes of M. marmoratus, hoping to provide insights into mitogenome rearrangement events in Myriapoda. In addition, our mitogenomic phylogenetic analyses showed that the main myriapod groups are monophyletic and supported the combination of the Pauropoda and Diplopoda to form the Dignatha. Within the Chilopoda, we suggest that Scutigeromorpha is a sister group to the Lithobiomorpha, Geophilomorpha, and Scolopendromorpha. We also identified a close relationship between the Lithobiomorpha and Geophilomorpha. The results also indicate that the mitogenome can be used as an effective mechanism to understand the phylogenetic relationships within Myriapoda.

Molecular phylogeny of the orb-weaving spider genus Leucauge and the intergeneric relationships of Leucauginae (Araneae, Tetragnathidae)

The tetragnathid genus Leucauge includes some of the most common orb-weaving spiders in the tropics. Although some species in this genus have attained relevance as model systems for several aspects of spider biology, our understanding of the generic diversity and evolutionary relationships among the species is poor. In this study we present the first attempt to determine the phylogenetic structure within Leucauge and the relationship of this genus with other genera of Leucauginae. This is based on DNA sequences from the five loci commonly used and Histone H4, used for the first time in spider phylogenetics. We also assess the informativeness of the standard markers and test for base composition biases in the dataset. Our results suggest that Leucauge is not monophyletic since species of the genera Opas, Opadometa, Mecynometa and Alcimosphenus are included within the current circumscription of the genus. Based on a phylogenetic re-circumscription of the genus to fulfil the requirement for monophyly of taxa, Leucauge White, 1841 is deemed to be a senior synonym of the genera Opas Pickard-Cambridge, 1896 revalidated synonymy, Mecynometa Simon, 1894 revalidated synonymy, Opadometa Archer, 1951 new synonymy and Alcimosphenus Simon, 1895 new synonymy. We identify groups of taxa critical for resolving relationships within Leucauginae and describe the limitations of the standard loci for accomplishing these resolutions.

Four myriapod relatives - but who are sisters? No end to debates on relationships among the four major myriapod subgroups

Background

Phylogenetic relationships among the myriapod subgroups Chilopoda, Diplopoda, Symphyla and Pauropoda are still not robustly resolved. The first phylogenomic study covering all subgroups resolved phylogenetic relationships congruently to morphological evidence but is in conflict with most previously published phylogenetic trees based on diverse molecular data. Outgroup choice and long-branch attraction effects were stated as possible explanations for these incongruencies. In this study, we addressed these issues by extending the myriapod and outgroup taxon sampling using transcriptome data.

Results

We generated new transcriptome data of 42 panarthropod species, including all four myriapod subgroups and additional outgroup taxa. Our taxon sampling was complemented by published transcriptome and genome data resulting in a supermatrix covering 59 species. We compiled two data sets, the first with a full coverage of genes per species (292 single-copy protein-coding genes), the second with a less stringent coverage (988 genes). We inferred phylogenetic relationships among myriapods using different data types, tree inference, and quartet computation approaches. Our results unambiguously support monophyletic Mandibulata and Myriapoda. Our analyses clearly showed that there is strong signal for a single unrooted topology, but a sensitivity of the position of the internal root on the choice of outgroups. However, we observe strong evidence for a clade Pauropoda+Symphyla, as well as for a clade Chilopoda+Diplopoda.

Conclusions

Our best quartet topology is incongruent with current morphological phylogenies which were supported in another phylogenomic study. AU tests and quartet mapping reject the quartet topology congruent to trees inferred with morphological characters. Moreover, quartet mapping shows that confounding signal present in the data set is sufficient to explain the weak signal for the quartet topology derived from morphological characters. Although outgroup choice affects results, our study could narrow possible trees to derivatives of a single quartet topology. For highly disputed relationships, we propose to apply a series of tests (AU and quartet mapping), since results of such tests allow to narrow down possible relationships and to rule out confounding signal.

Measuring Genome Sizes Using Read-Depth, k-mers, and Flow Cytometry: Methodological Comparisons in Beetles (Coleoptera)

Measuring genome size across different species can yield important insights into evolution of the genome and allow for more informed decisions when designing next-generation genomic sequencing projects. New techniques for estimating genome size using shallow genomic sequence data have emerged which have the potential to augment our knowledge of genome sizes, yet these methods have only been used in a limited number of empirical studies. In this project, we compare estimation methods using next-generation sequencing (k-mer methods and average read depth of single-copy genes) to measurements from flow cytometry, a standard method for genome size measures, using ground beetles (Carabidae) and other members of the beetle suborder Adephaga as our test system. We also present a new protocol for using read-depth of single-copy genes to estimate genome size. Additionally, we report flow cytometry measurements for five previously unmeasured carabid species, as well as 21 new draft genomes and six new draft transcriptomes across eight species of adephagan beetles. No single sequence-based method performed well on all species, and all tended to underestimate the genome sizes, although only slightly in most samples. For one species, Bembidion sp. nr. transversale, most sequence-based methods yielded estimates half the size suggested by flow cytometry.

The complete mitochondrial genome sequence of Scolopendra mutilans L. Koch, 1878 (Scolopendromorpha, Scolopendridae), with a comparative analysis of other centipede genomes

Scolopendramutilans L. Koch, 1878 is an important Chinese animal with thousands of years of medicinal history. However, the genomic information of this species is limited, which hinders its further application. Here, the complete mitochondrial genome (mitogenome) of S.mutilans was sequenced and assembled by next-generation sequencing. The genome is 15,011 bp in length, consisting of 13 protein-coding genes (PCGs), 14 tRNA genes, and two rRNA genes. Most PCGs start with the ATN initiation codon, and all PCGs have the conventional stop codons TAA and TAG. The S.mutilans mitogenome revealed nine simple sequence repeats (SSRs), and an obviously lower GC content compared with other seven centipede mitogenomes previously sequenced. After analysis of homologous regions between the eight centipede mitogenomes, the S.mutilans mitogenome further showed clear genomic rearrangements. The phylogenetic analysis of eight centipedes using 13 conserved PCG genes was finally performed. The phylogenetic reconstructions showed Scutigeromorpha as a separate group, and Scolopendromorpha in a sister-group relationship with Lithobiomorpha and Geophilomorpha. Collectively, the S.mutilans mitogenome provided new genomic resources, which will improve its medicinal research and applications in the future.

Major Revisions in Arthropod Phylogeny Through Improved Supermatrix, With Support for Two Possible Waves of Land Invasion by Chelicerates

Deep phylogeny involving arthropod lineages is difficult to recover because the erosion of phylogenetic signals over time leads to unreliable multiple sequence alignment (MSA) and subsequent phylogenetic reconstruction. One way to alleviate the problem is to assemble a large number of gene sequences to compensate for the weakness in each individual gene. Such an approach has led to many robustly supported but contradictory phylogenies. A close examination shows that the supermatrix approach often suffers from two shortcomings. The first is that MSA is rarely checked for reliability and, as will be illustrated, can be poor. The second is that, to alleviate the problem of homoplasy at the third codon position of protein-coding genes due to convergent evolution of nucleotide frequencies, phylogeneticists may remove or degenerate the third codon position but may do it improperly and introduce new biases. We performed extensive reanalysis of one of such "big data" sets to highlight these two problems, and demonstrated the power and benefits of correcting or alleviating these problems. Our results support a new group with Xiphosura and Arachnopulmonata (Tetrapulmonata + Scorpiones) as sister taxa. This favors a new hypothesis in which the ancestor of Xiphosura and the extinct Eurypterida (sea scorpions, of which many later forms lived in brackish or freshwater) returned to the sea after the initial chelicerate invasion of land. Our phylogeny is supported even with the original data but processed with a new "principled" codon degeneration. We also show that removing the 1673 codon sites with both AGN and UCN codons (encoding serine) in our alignment can partially reconcile discrepancies between nucleotide-based and AA-based tree, partly because two sequences, one with AGN and the other with UCN, would be identical at the amino acid level but quite different at the nucleotide level.

Arthropod venoms: Biochemistry, ecology and evolution

Comprising of over a million described species of highly diverse invertebrates, Arthropoda is amongst the most successful animal lineages to have colonized aerial, terrestrial, and aquatic domains. Venom, one of the many fascinating traits to have evolved in various members of this phylum, has underpinned their adaptation to diverse habitats. Over millions of years of evolution, arthropods have evolved ingenious ways of delivering venom in their targets for self-defence and predation. The morphological diversity of venom delivery apparatus in arthropods is astounding, and includes extensively modified pedipalps, tail (telson), mouth parts (hypostome), fangs, appendages (maxillulae), proboscis, ovipositor (stinger), and hair (urticating bristles). Recent investigations have also unravelled an astonishing venom biocomplexity with molecular scaffolds being recruited from a multitude of protein families. Venoms are a remarkable bioresource for discovering lead compounds in targeted therapeutics. Several components with prospective applications in the development of advanced lifesaving drugs and environment friendly bio-insecticides have been discovered from arthropod venoms. Despite these fascinating features, the composition, bioactivity, and molecular evolution of venom in several arthropod lineages remains largely understudied. This review highlights the prevalence of venom, its mode of toxic action, and the evolutionary dynamics of venom in Arthropoda, the most speciose phylum in the animal kingdom.

A general theory of genital homologies for the Hexapoda (Pancrustacea) derived from skeletomuscular correspondences, with emphasis on the Endopterygota

No consensus exists for the homology and terminology of the male genitalia of the Hexapoda despite over a century of debate. Based on dissections and the literature, genital skeletomusculature was compared across the Hexapoda and contrasted with the Remipedia, the closest pancrustacean outgroup. The pattern of origin and insertion for extrinsic and intrinsic genitalic musculature was found to be consistent among the Ectognatha, Protura, and the Remipedia, allowing for the inference of homologies given recent phylogenomic studies. The penis of the Hexapoda is inferred to be derived from medially-fused primary gonopods (gonopore-bearing limbs), while the genitalia of the Ectognatha are inferred to include both the tenth-segmental penis and the ninth-segmental secondary gonopods, similar to the genitalia of female insects which comprise gonopods of the eighth and ninth segments. A new nomenclatural system for hexapodan genitalic musculature is presented and applied, and a general list of anatomical concepts is provided. Novel and refined homologies are proposed for all hexapodan orders, and a series of groundplans are postulated. Emphasis is placed on the Endopterygota, for which fine-grained transition series are hypothesized given observed skeletomuscular correspondences.

Molecular phylogenetics and species-level systematics of Baylisascaris

Nucleotide sequences representing nine genes and five presumptive genetic loci were used to infer phylogenetic relationships among seven Baylisascaris species, including one species with no previously available molecular data. These genes were used to test the species status of B. procyonis and B. columnaris using a coalescent approach. Phylogenetic analysis based on combined analysis of sequence data strongly supported monophyly of the genus and separated the species into two main clades. Clade 1 included B. procyonis, B. columnaris, and B. devosi, species hosted by musteloid carnivores. Clade 2 included B. transfuga and B. schroederi from ursids, B. ailuri, a species from the red panda (a musteloid), and B. tasmaniensis from a marsupial. Within clade 2, geographic isolates of B. transfuga, B. schroederi (from giant panda), and B. ailuri formed a strongly supported clade. In certain analyses (e.g., some single genes), B. tasmaniensis was sister to all other Baylisascaris species rather than sister to the species from ursids and red panda. Using one combination of priors corresponding to moderate population size and shallow genetic divergence, the multispecies coalescent analysis of B. procyonis and B. columnaris yielded moderate support (posterior probability 0.91) for these taxa as separate species. However, other prior combinations yielded weak or no support for delimiting these taxa as separate species. Similarly, tree topologies constrained to represent reciprocal monophyly of B. columnaris and B. procyonis individuals (topologies consistent with separate species) were significantly worse in some cases, but not others, depending on the dataset analyzed. An expanded analysis of SNPs and other genetic markers that were previously suggested to distinguish between individuals of B. procyonis and B. columnaris was made by characterization of additional individual nematodes. The results suggest that many of these SNPs do not represent fixed differences between nematodes derived from raccoon and skunk hosts.

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A phylogenetic hypothesis for Baylisascaris species was produced using nine genes.

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Genetic data was generated for two new species- B. devosi and B. tasmaniensis.

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Baylisascaris devosi and B. tasmaniensis were part of a monophyletic Baylisascaris.

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B. procyonis (raccoon) and B. columnaris (skunk) could not be reliably distinguished.

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Established SNPs may not be diagnostic for Baylisascaris from raccoons and skunks.

Molecular phylogeny of Culex subgenus Melanoconion (Diptera: Culicidae) based on nuclear and mitochondrial protein-coding genes

The subgenus Melanoconion of the mosquito genus Culex is taxonomically diverse and is widely distributed in the Neotropical Region, with 10 species occurring in the Nearctic Region. Species of this subgenus pose a taxonomical challenge because morphological identification is based largely on anatomical characters of the male genitalia. We addressed the monophyly of the Spissipes and Melanoconion Sections of the subgenus Melanoconion and some of the informal groups in each section. Our sample taxa included 97 specimens representing 43 species, from which we analysed fragments of two single-copy nuclear genes (CAD, HB) and one mitochondrial gene (COI). Phylogenetic relationships within the subgenus are presented based on results of maximum-likelihood and Bayesian analyses using a multi-locus matrix of DNA sequences. We show a molecular phylogeny of Melanoconion in which both sections were recovered as monophyletic groups. The monophyly of the Atratus and Pilosus groups was confirmed. Within each section, other monophyletic groups were recovered highlighting the potential need for future nomenclature rearrangement. The phylogenetic signal contained in nuclear genes, when analysed together, was more informative than each gene analysed separately, corroborating monophyly of Melanoconion relative to Culex (Culex) species included in the analyses, the Melanoconion and Spissipes Sections and some species groups. Our results provide new information for the classification of the subgenus and additional data that can be used to improve species identification when a more representative taxon sampling is available.

More on the Best Evolutionary Rate for Phylogenetic Analysis

The accumulation of genome-scale molecular data sets for nonmodel taxa brings us ever closer to resolving the tree of life of all living organisms. However, despite the depth of data available, a number of studies that each used thousands of genes have reported conflicting results. The focus of phylogenomic projects must thus shift to more careful experimental design. Even though we still have a limited understanding of what are the best predictors of the phylogenetic informativeness of a gene, there is wide agreement that one key factor is its evolutionary rate; but there is no consensus as to whether the rates derived as optimal in various analytical, empirical, and simulation approaches have any general applicability. We here use simulations to infer optimal rates in a set of realistic phylogenetic scenarios with varying tree sizes, numbers of terminals, and tree shapes. Furthermore, we study the relationship between the optimal rate and rate variation among sites and among lineages. Finally, we examine how well the predictions made by a range of experimental design methods correlate with the observed performance in our simulations.We find that the optimal level of divergence is surprisingly robust to differences in taxon sampling and even to among-site and among-lineage rate variation as often encountered in empirical data sets. This finding encourages the use of methods that rely on a single optimal rate to predict a gene's utility. Focusing on correct recovery either of the most basal node in the phylogeny or of the entire topology, the optimal rate is about 0.45 substitutions from root to tip in average Yule trees and about 0.2 in difficult trees with short basal and long-apical branches, but all rates leading to divergence levels between about 0.1 and 0.5 perform reasonably well.Testing the performance of six methods that can be used to predict a gene's utility against our simulation results, we find that the probability of resolution, signal-noise analysis, and Fisher information are good predictors of phylogenetic informativeness, but they require specification of at least part of a model tree. Likelihood quartet mapping also shows very good performance but only requires sequence alignments and is thus applicable without making assumptions about the phylogeny. Despite them being the most commonly used methods for experimental design, geometric quartet mapping and the integration of phylogenetic informativeness curves perform rather poorly in our comparison. Instead of derived predictors of phylogenetic informativeness, we suggest that the number of sites in a gene that evolve at near-optimal rates (as inferred here) could be used directly to prioritize genes for phylogenetic inference. In combination with measures of model fit, especially with respect to compositional biases and among-site and among-lineage rate variation, such an approach has the potential to greatly improve marker choice and should be tested on empirical data.

Molecular Phylogeny and Revision of Copepod Orders (Crustacea: Copepoda)

For the first time, the phylogenetic relationships between representatives of all 10 copepod orders have been investigated using 28S and 18S rRNA, Histone H3 protein and COI mtDNA. The monophyly of Copepoda (including Platycopioida Fosshagen, 1985) is demonstrated for the first time using molecular data. Maxillopoda is rejected, as it is a polyphyletic group. The monophyly of the major subgroups of Copepoda, including Progymnoplea Lang, 1948 (=Platycopioida); Neocopepoda Huys and Boxshall, 1991; Gymnoplea Giesbrecht, 1892 (=Calanoida Sars, 1903); and Podoplea Giesbrecht, 1892, are supported in this study. Seven copepod orders are monophyletic, including Platycopioida, Calanoida, Misophrioida Gurney, 1933; Monstrilloida Sars, 1901; Siphonostomatoida Burmeister, 1834; Gelyelloida Huys, 1988; and Mormonilloida Boxshall, 1979. Misophrioida (=Propodoplea Lang, 1948) is the most basal Podoplean order. The order Cyclopoida Burmeister, 1835, is paraphyletic and now encompasses Poecilostomatoida Thorell, 1859, as a sister to the family Schminkepinellidae Martinez Arbizu, 2006. Within Harpacticoida Sars, 1903, both sections, Polyarthra Lang, 1948, and Oligoarthra Lang, 1948, are monophyletic, but not sister groups. The order Canuelloida is proposed while maintaining the order Harpacticoida s. str. (Oligoarthra). Cyclopoida, Harpacticoida and Cyclopinidae are redefined, while Canuelloida ordo. nov., Smirnovipinidae fam. nov. and Cyclopicinidae fam. nov are proposed as new taxa.

Molecular phylogeny reveals food plasticity in the evolution of true ladybird beetles (Coleoptera: Coccinellidae: Coccinellini)

BACKGROUND

The tribe Coccinellini is a group of relatively large ladybird beetles that exhibits remarkable morphological and biological diversity. Many species are aphidophagous, feeding as larvae and adults on aphids, but some species also feed on other hemipterous insects (i.e., heteropterans, psyllids, whiteflies), beetle and moth larvae, pollen, fungal spores, and even plant tissue. Several species are biological control agents or widespread invasive species (e.g., Harmonia axyridis (Pallas)). Despite the ecological importance of this tribe, relatively little is known about the phylogenetic relationships within it. The generic concepts within the tribe Coccinellini are unstable and do not reflect a natural classification, being largely based on regional revisions. This impedes the phylogenetic study of important traits of Coccinellidae at a global scale (e.g. the evolution of food preferences and biogeography).

RESULTS

We present the most comprehensive phylogenetic analysis of Coccinellini to date, based on three nuclear and one mitochondrial gene sequences of 38 taxa, which represent all major Coccinellini lineages. The phylogenetic reconstruction supports the monophyly of Coccinellini and its sister group relationship to Chilocorini. Within Coccinellini, three major clades were recovered that do not correspond to any previously recognised divisions, questioning the traditional differentiation between Halyziini, Discotomini, Tytthaspidini, and Singhikaliini. Ancestral state reconstructions of food preferences and morphological characters support the idea of aphidophagy being the ancestral state in Coccinellini. This indicates a transition from putative obligate scale feeders, as seen in the closely related Chilocorini, to more agile general predators.

CONCLUSIONS

Our results suggest that the classification of Coccinellini has been misled by convergence in morphological traits. The evolutionary history of Coccinellini has been very dynamic in respect to changes in host preferences, involving multiple independent host switches from different insect orders to fungal spores and plants tissues. General predation on ephemeral aphids might have created an opportunity to easily adapt to mixed or specialised diets (e.g. obligate mycophagy, herbivory, predation on various hemipteroids or larvae of leaf beetles (Chrysomelidae)). The generally long-lived adults of Coccinellini can consume pollen and floral nectars, thereby surviving periods of low prey frequency. This capacity might have played a central role in the diversification history of Coccinellini.

Complete mitochondrial genomes of two flat-backed millipedes by next-generation sequencing (Diplopoda, Polydesmida)

A lack of mitochondrial genome data from myriapods is hampering progress across genetic, systematic, phylogenetic and evolutionary studies. Here, the complete mitochondrial genomes of two millipedes, Asiomorphacoarctata Saussure, 1860 (Diplopoda: Polydesmida: Paradoxosomatidae) and Xystodesmus sp. (Diplopoda: Polydesmida: Xystodesmidae) were assembled with high coverage using Illumina sequencing data. The mitochondrial genomes of the two newly sequenced species are circular molecules of 15,644 bp and 15,791 bp, within which the typical mitochondrial genome complement of 13 protein-coding genes, 22 tRNAs and two ribosomal RNA genes could be identified. The mitochondrial genome of Asiomorphacoarctata is the first complete sequence in the family Paradoxosomatidae (Diplopoda: Polydesmida) and the gene order of the two flat-backed millipedes is novel among known myriapod mitochondrial genomes. Unique translocations have occurred, including inversion of one half of the two genomes with respect to other millipede genomes. Inversion of the entire side of a genome (trnF-nad5-trnH-nad4-nad4L, trnP, nad1-trnL2-trnL1-rrnL-trnV-rrnS, trnQ, trnC and trnY) could constitute a common event in the order Polydesmida. Last, our phylogenetic analyses recovered the monophyletic Progoneata, subphylum Myriapoda and four internal classes.

Phylogenomic analysis of Copepoda (Arthropoda, Crustacea) reveals unexpected similarities with earlier proposed morphological phylogenies

BACKGROUND

Copepods play a critical role in marine ecosystems but have been poorly investigated in phylogenetic studies. Morphological evidence supports the monophyly of copepods, whereas interordinal relationships continue to be debated. In particular, the phylogenetic position of the order Harpacticoida is still ambiguous and inconsistent among studies. Until now, a small number of molecular studies have been done using only a limited number or even partial genes and thus there is so far no consensus at the order-level.

RESULTS

This study attempted to resolve phylogenetic relationships among and within four major copepod orders including Harpacticoida and the phylogenetic position of Copepoda among five other crustacean groups (Anostraca, Cladocera, Sessilia, Amphipoda, and Decapoda) using 24 nuclear protein-coding genes. Phylogenomics has confirmed the monophyly of Copepoda and Podoplea. However, this study reveals surprising differences with the majority of the copepod phylogenies and unexpected similarities with postembryonic characters and earlier proposed morphological phylogenies; More precisely, Cyclopoida is more closely related to Siphonostomatoida than to Harpacticoida which is likely the most basally-branching group of Podoplea. Divergence time estimation suggests that the origin of Harpacticoida can be traced back to the Devonian, corresponding well with recently discovered fossil evidence. Copepoda has a close affinity to the clade of Malacostraca and Thecostraca but not to Branchiopoda. This result supports the hypothesis of the newly proposed clades, Communostraca, Multicrustacea, and Allotriocarida but further challenges the validity of Hexanauplia and Vericrustacea.

CONCLUSIONS

The first phylogenomic study of Copepoda provides new insights into taxonomic relationships and represents a valuable resource that improves our understanding of copepod evolution and their wide range of ecological adaptations.

Ten genes and two topologies: an exploration of higher relationships in skipper butterflies (Hesperiidae)

Despite multiple attempts to infer the higher-level phylogenetic relationships of skipper butterflies (Family Hesperiidae), uncertainties in the deep clade relationships persist. The most recent phylogenetic analysis included fewer than 30% of known genera and data from three gene markers. Here we reconstruct the higher-level relationships with a rich sampling of ten nuclear and mitochondrial markers (7,726 bp) from 270 genera and find two distinct but equally plausible topologies among subfamilies at the base of the tree. In one set of analyses, the nuclear markers suggest two contrasting topologies, one of which is supported by the mitochondrial dataset. However, another set of analyses suggests mito-nuclear conflict as the reason for topological incongruence. Neither topology is strongly supported, and we conclude that there is insufficient phylogenetic evidence in the molecular dataset to resolve these relationships. Nevertheless, taking morphological characters into consideration, we suggest that one of the topologies is more likely.

A Genome-Scale Investigation of How Sequence, Function, and Tree-Based Gene Properties Influence Phylogenetic Inference

Molecular phylogenetic inference is inherently dependent on choices in both methodology and data. Many insightful studies have shown how choices in methodology, such as the model of sequence evolution or optimality criterion used, can strongly influence inference. In contrast, much less is known about the impact of choices in the properties of the data, typically genes, on phylogenetic inference. We investigated the relationships between 52 gene properties (24 sequence-based, 19 function-based, and 9 tree-based) with each other and with three measures of phylogenetic signal in two assembled data sets of 2,832 yeast and 2,002 mammalian genes. We found that most gene properties, such as evolutionary rate (measured through the percent average of pairwise identity across taxa) and total tree length, were highly correlated with each other. Similarly, several gene properties, such as gene alignment length, Guanine-Cytosine content, and the proportion of tree distance on internal branches divided by relative composition variability (treeness/RCV), were strongly correlated with phylogenetic signal. Analysis of partial correlations between gene properties and phylogenetic signal in which gene evolutionary rate and alignment length were simultaneously controlled, showed similar patterns of correlations, albeit weaker in strength. Examination of the relative importance of each gene property on phylogenetic signal identified gene alignment length, alongside with number of parsimony-informative sites and variable sites, as the most important predictors. Interestingly, the subsets of gene properties that optimally predicted phylogenetic signal differed considerably across our three phylogenetic measures and two data sets; however, gene alignment length and RCV were consistently included as predictors of all three phylogenetic measures in both yeasts and mammals. These results suggest that a handful of sequence-based gene properties are reliable predictors of phylogenetic signal and could be useful in guiding the choice of phylogenetic markers.

Exploring Phylogenetic Relationships within Myriapoda and the Effects of Matrix Composition and Occupancy on Phylogenomic Reconstruction

Myriapods, including the diverse and familiar centipedes and millipedes, are one of the dominant terrestrial arthropod groups. Although molecular evidence has shown that Myriapoda is monophyletic, its internal phylogeny remains contentious and understudied, especially when compared to those of Chelicerata and Hexapoda. Until now, efforts have focused on taxon sampling (e.g., by including a handful of genes from many species) or on maximizing matrix size (e.g., by including hundreds or thousands of genes in just a few species), but a phylogeny maximizing sampling at both levels remains elusive. In this study, we analyzed 40 Illumina transcriptomes representing 3 of the 4 myriapod classes (Diplopoda, Chilopoda, and Symphyla); 25 transcriptomes were newly sequenced to maximize representation at the ordinal level in Diplopoda and at the family level in Chilopoda. Ten supermatrices were constructed to explore the effect of several potential phylogenetic biases (e.g., rate of evolution, heterotachy) at 3 levels of gene occupancy per taxon (50%, 75%, and 90%). Analyses based on maximum likelihood and Bayesian mixture models retrieved monophyly of each myriapod class, and resulted in 2 alternative phylogenetic positions for Symphyla, as sister group to Diplopoda + Chilopoda, or closer to Diplopoda, the latter hypothesis having been traditionally supported by morphology. Within centipedes, all orders were well supported, but 2 deep nodes remained in conflict in the different analyses despite dense taxon sampling at the family level. Relationships among centipede orders in all analyses conducted with the most complete matrix (90% occupancy) are at odds not only with the sparser but more gene-rich supermatrices (75% and 50% supermatrices) and with the matrices optimizing phylogenetic informativeness or most conserved genes, but also with previous hypotheses based on morphology, development, or other molecular data sets. Our results indicate that a high percentage of ribosomal proteins in the most complete matrices, in conjunction with distance from the root, can act in concert to compromise the estimated relationships within the ingroup. We discuss the implications of these findings in the context of the ever more prevalent quest for completeness in phylogenomic studies.

A molecular palaeobiological exploration of arthropod terrestrialization

Understanding animal terrestrialization, the process through which animals colonized the land, is crucial to clarify extant biodiversity and biological adaptation. Arthropoda (insects, spiders, centipedes and their allies) represent the largest majority of terrestrial biodiversity. Here we implemented a molecular palaeobiological approach, merging molecular and fossil evidence, to elucidate the deepest history of the terrestrial arthropods. We focused on the three independent, Palaeozoic arthropod terrestrialization events (those of Myriapoda, Hexapoda and Arachnida) and showed that a marine route to the colonization of land is the most likely scenario. Molecular clock analyses confirmed an origin for the three terrestrial lineages bracketed between the Cambrian and the Silurian. While molecular divergence times for Arachnida are consistent with the fossil record, Myriapoda are inferred to have colonized land earlier, substantially predating trace or body fossil evidence. An estimated origin of myriapods by the Early Cambrian precedes the appearance of embryophytes and perhaps even terrestrial fungi, raising the possibility that terrestrialization had independent origins in crown-group myriapod lineages, consistent with morphological arguments for convergence in tracheal systems.This article is part of the themed issue 'Dating species divergences using rocks and clocks'.

Ostracod (Ostracoda, Crustacea) genomics - Promises and challenges

Ostracods are well-suited model organisms for evolutionary research. Classic genetic techniques have mostly been used for phylogenetic studies on Ostracoda and were somewhat affected by the lack of large numbers of suitable markers. Genomic methods with their huge potential have so far rarely been applied to this group of crustaceans. We provide relevant examples of genomic studies on other organisms to propose future avenues of genomic ostracod research. At the same time, we suggest solutions to the potential problems in ostracods that the application of genomic techniques might present.

Power, resolution and bias: recent advances in insect phylogeny driven by the genomic revolution

Our understanding on the phylogenetic relationships of insects has been revolutionised in the last decade by the proliferation of next generation sequencing technologies (NGS). NGS has allowed insect systematists to assemble very large molecular datasets that include both model and non-model organisms. Such datasets often include a large proportion of the total number of protein coding sequences available for phylogenetic comparison. We review some early entomological phylogenomic studies that employ a range of different data sampling protocols and analyses strategies, illustrating a fundamental renaissance in our understanding of insect evolution all driven by the genomic revolution. The analysis of phylogenomic datasets is challenging because of their size and complexity, and it is obvious that the increasing size alone does not ensure that phylogenetic signal overcomes systematic biases in the data. Biases can be due to various factors such as the method of data generation and assembly, or intrinsic biological feature of the data per se, such as similarities due to saturation or compositional heterogeneity. Such biases often cause violations in the underlying assumptions of phylogenetic models. We review some of the bioinformatics tools available and being developed to detect and minimise systematic biases in phylogenomic datasets. Phylogenomic-scale data coupled with sophisticated analyses will revolutionise our understanding of insect functional genomics. This will illuminate the relationship between the vast range of insect phenotypic diversity and underlying genetic diversity. In combination with rapidly developing methods to estimate divergence times, these analyses will also provide a compelling view of the rates and patterns of lineagenesis (birth of lineages) over the half billion years of insect evolution.

Phylotranscriptomic Analysis Based on Coalescence was Less Influenced by the Evolving Rates and the Number of Genes: A Case Study in Ericales

Advances in high-throughput sequencing have generated a vast amount of transcriptomic data that are being increasingly used in phylogenetic reconstruction. However, processing the vast datasets for a huge number of genes and even identifying optimal analytical methodology are challenging. Through de novo sequenced and retrieved data from public databases, we identified 221 orthologous protein-coding genes to reconstruct the phylogeny of Ericales, an order characterized by rapid ancient radiation. Seven species representing different families in Ericales were used as in-groups. Both concatenation and coalescence methods yielded the same well-supported topology as previous studies, with only two nodes conflicting with previously reported relationships. The results revealed that a partitioning strategy could improve the traditional concatenation methodology. Rapidly evolving genes negatively affected the concatenation analysis, while slowly evolving genes slightly affected the coalescence analysis. The coalescence methods usually accommodated rate heterogeneity better and required fewer genes to yield well-supported topologies than the concatenation methods with both real and simulated data.

Successful Recovery of Nuclear Protein-Coding Genes from Small Insects in Museums Using Illumina Sequencing

In this paper we explore high-throughput Illumina sequencing of nuclear protein-coding, ribosomal, and mitochondrial genes in small, dried insects stored in natural history collections. We sequenced one tenebrionid beetle and 12 carabid beetles ranging in size from 3.7 to 9.7 mm in length that have been stored in various museums for 4 to 84 years. Although we chose a number of old, small specimens for which we expected low sequence recovery, we successfully recovered at least some low-copy nuclear protein-coding genes from all specimens. For example, in one 56-year-old beetle, 4.4 mm in length, our de novo assembly recovered about 63% of approximately 41,900 nucleotides in a target suite of 67 nuclear protein-coding gene fragments, and 70% using a reference-based assembly. Even in the least successfully sequenced carabid specimen, reference-based assembly yielded fragments that were at least 50% of the target length for 34 of 67 nuclear protein-coding gene fragments. Exploration of alternative references for reference-based assembly revealed few signs of bias created by the reference. For all specimens we recovered almost complete copies of ribosomal and mitochondrial genes. We verified the general accuracy of the sequences through comparisons with sequences obtained from PCR and Sanger sequencing, including of conspecific, fresh specimens, and through phylogenetic analysis that tested the placement of sequences in predicted regions. A few possible inaccuracies in the sequences were detected, but these rarely affected the phylogenetic placement of the samples. Although our sample sizes are low, an exploratory regression study suggests that the dominant factor in predicting success at recovering nuclear protein-coding genes is a high number of Illumina reads, with success at PCR of COI and killing by immersion in ethanol being secondary factors; in analyses of only high-read samples, the primary significant explanatory variable was body length, with small beetles being more successfully sequenced.

Phylogenomic analyses resolve an ancient trichotomy at the base of Ischyropsalidoidea (Arachnida, Opiliones) despite high levels of gene tree conflict and unequal minority resolution frequencies

Phylogenetic resolution of ancient rapid radiations has remained problematic despite major advances in statistical approaches and DNA sequencing technologies. Here we report on a combined phylogenetic approach utilizing transcriptome data in conjunction with Sanger sequence data to investigate a tandem of ancient divergences in the harvestmen superfamily Ischyropsalidoidea (Arachnida, Opiliones, Dyspnoi). We rely on Sanger sequences to resolve nodes within and between closely related genera, and use RNA-seq data from a subset of taxa to resolve a short and ancient internal branch. We use several analytical approaches to explore this succession of ancient diversification events, including concatenated and coalescent-based analyses and maximum likelihood gene trees for each locus. We evaluate the robustness of phylogenetic inferences using a randomized locus sub-sampling approach, and find congruence across these methods despite considerable incongruence across gene trees. Incongruent gene trees are not recovered in frequencies expected from a simple multispecies coalescent model, and we reject incomplete lineage sorting as the sole contributor to gene tree conflict. Using these approaches we attain robust support for higher-level phylogenetic relationships within Ischyropsalidoidea.

The decapod red pigment-concentrating hormone (Panbo-RPCH) is the first identified neuropeptide of the order Plecoptera and is interpreted as homoplastic character state

This paper presents the first neuropeptide structure, identified by mass spectrometry, in two species of Plectoptera (stoneflies) and in one species of the coleopteran family Lycidae. In all three species, the octapeptide Panbo-RPCH (first identified in Pandalus borealis as a red pigment-concentrating hormone: pGlu-Leu-Asn-Phe-Ser-Pro-Gly-Trp amide) is present. A review of the literature available on invertebrate neuropeptides that are identified or predicted from expressed sequence tags, transcriptome shotgun assemblies, and from fully sequenced genomes, show that Panbo-RPCH is found in Malacostraca (Crustacea) and certain hemipteran Heteroptera (Insecta). To date, Panbo-RPCH has not been shown present in non-Malacostracan crustaceans, nor in basal taxa of the Insecta (Archaeognatha, Zygentoma, Ephemeroptera, Odonata). The present data adds to knowledge on the distribution of Panbo-RPCH, and when taking into account the most accepted, current phylogenetics of the Crustacea-Hexapoda relationship, this distribution of Panbo-RPCH in Malacostraca, Plecoptera, some hemipteran Heteroptera and in Coleoptera (Lycidae) can best be explained by homoplasy, implying parallel evolution.

Olfactory pathway in Xibalbanus tulumensis: remipedian hemiellipsoid body as homologue of hexapod mushroom body

The Remipedia have been proposed to be the crustacean sister group of the Hexapoda. These blind cave animals heavily rely on their chemical sense and are thus rewarding subjects for the analysis of olfactory pathways. The evolution of these pathways as a character for arthropod phylogeny has recently received increasing attention. Here, we investigate the situation in Xibalbanus tulumensis by focal dye injections and immunolabelling of the catalytic subunit of the cAMP-dependent protein kinase (DC0), an enzyme particularly enriched in insect mushroom bodies. DC0 labelling of the hemiellipsoid body suggests its subdivision into a cap-like and a core neuropil. Immunofluorescence of the enzyme glutamic acid decarboxylase (GAD), which synthesizes γ-aminobutyric acid (GABA), has revealed a cluster of GABAergic interneurons in the hemiellipsoid body, reminiscent of the characteristic feedback neurons of the mushroom body. Thus, the hemiellipsoid body of Xibalbanus shares many of the characteristics of insect mushroom bodies. Nevertheless, the general neuroanatomy of the olfactory pathway in the Remipedia strongly corresponds to the malacostracan ground pattern. Given that the Remipedia are probably the sister group of the Hexapoda, the phylogenetic appearance of the typical neuropilar compartments in the insect mushroom body has to be assigned to the origins of the Hexapoda.

Selecting Question-Specific Genes to Reduce Incongruence in Phylogenomics: A Case Study of Jawed Vertebrate Backbone Phylogeny

Incongruence between different phylogenomic analyses is the main challenge faced by phylogeneticists in the genomic era. To reduce incongruence, phylogenomic studies normally adopt some data filtering approaches, such as reducing missing data or using slowly evolving genes, to improve the signal quality of data. Here, we assembled a phylogenomic data set of 58 jawed vertebrate taxa and 4682 genes to investigate the backbone phylogeny of jawed vertebrates under both concatenation and coalescent-based frameworks. To evaluate the efficiency of extracting phylogenetic signals among different data filtering methods, we chose six highly intractable internodes within the backbone phylogeny of jawed vertebrates as our test questions. We found that our phylogenomic data set exhibits substantial conflicting signal among genes for these questions. Our analyses showed that non-specific data sets that are generated without bias toward specific questions are not sufficient to produce consistent results when there are several difficult nodes within a phylogeny. Moreover, phylogenetic accuracy based on non-specific data is considerably influenced by the size of data and the choice of tree inference methods. To address such incongruences, we selected genes that resolve a given internode but not the entire phylogeny. Notably, not only can this strategy yield correct relationships for the question, but it also reduces inconsistency associated with data sizes and inference methods. Our study highlights the importance of gene selection in phylogenomic analyses, suggesting that simply using a large amount of data cannot guarantee correct results. Constructing question-specific data sets may be more powerful for resolving problematic nodes.

A survey of conservation of sea spider and Drosophila Hox protein activities

Hox proteins have well-established functions in development and evolution, controlling the final morphology of bilaterian animals. The common phylogenetic origin of Hox proteins and the associated evolutionary diversification of protein sequences provide a unique framework to explore the relationship between changes in protein sequence and function. In this study, we aimed at questioning how sequence variation within arthropod Hox proteins influences function. This was achieved by exploring the functional impact of sequence conservation/divergence of the Hox genes, labial, Sex comb reduced, Deformed, Ultrabithorax and abdominalA from two distant arthropods, the sea spider and the well-studied Drosophila. Results highlight a correlation between sequence conservation within the homeodomain and the degree of functional conservation, and identify a novel functional domain in the Labial protein.

Are 100 enough? Inferring acanthomorph teleost phylogeny using Anchored Hybrid Enrichment

BACKGROUND

The past decade has witnessed remarkable progress towards resolution of the Tree of Life. However, despite the increased use of genomic scale datasets, some phylogenetic relationships remain difficult to resolve. Here we employ anchored phylogenomics to capture 107 nuclear loci in 29 species of acanthomorph teleost fishes, with 25 of these species sampled from the recently delimited clade Ovalentaria. Previous studies employing multilocus nuclear exon datasets have not been able to resolve the nodes at the base of the Ovalentaria tree with confidence. Here we test whether a phylogenomic approach will provide better support for these nodes, and if not, why this may be.

RESULTS

After using a novel method to account for paralogous loci, we estimated phylogenies with maximum likelihood and species tree methods using DNA sequence alignments of over 80,000 base pairs. Several key relationships within Ovalentaria are well resolved, including 1) the sister taxon relationship between Cichlidae and Pholidichthys, 2) a clade containing blennies, grammas, clingfishes, and jawfishes, and 3) monophyly of Atherinomorpha (topminnows, flyingfishes, and silversides). However, many nodes in the phylogeny associated with the early diversification of Ovalentaria are poorly resolved in several analyses. Through the use of rarefaction curves we show that limited phylogenetic resolution among the earliest nodes in the Ovalentaria phylogeny does not appear to be due to a deficiency of data, as average global node support ceases to increase when only 1/3rd of the sampled loci are used in analyses. Instead this lack of resolution may be driven by model misspecification as a Bayesian mixed model analysis of the amino acid dataset provided good support for parts of the base of the Ovalentaria tree.

CONCLUSIONS

Although it does not appear that the limited phylogenetic resolution among the earliest nodes in the Ovalentaria phylogeny is due to a deficiency of data, it may be that both stochastic and systematic error resulting from model misspecification play a role in the poor resolution at the base of the Ovalentaria tree as a Bayesian approach was able to resolve some of the deeper nodes, where the other methods failed.

Three Halloween genes from the Varroa mite, Varroa destructor (Anderson & Trueman) and their expression during reproduction

The ecdysteroid biosynthetic pathway involves sequential enzymatic hydroxylations by a group of enzymes collectively known as Halloween gene proteins. Complete sequences for three Halloween genes, spook (Vdspo), disembodied (Vddib) and shade (Vdshd), were identified in varroa mites and sequenced. Phylogenetic analyses of predicted amino acid sequences for Halloween orthologues showed that the acarine orthologues were distantly associated with insect and crustacean clades indicating that acarine genes had more ancestral characters. The lack of orthologues or pseudogenes for remaining genes suggests these pathway elements had not evolved in ancestral arthropods. Vdspo transcript levels were highest in gut tissues, while Vddib transcript levels were highest in ovary-lyrate organs. In contrast, Vdshd transcript levels were lower overall but present in both gut and ovary-lyrate organs. All three transcripts were present in eggs removed from gravid female mites. A brood cell invasion assay was developed for acquiring synchronously staged mites. Mites within 4 h of entering a brood cell had transcript levels of all three that were not significantly different from mites on adult bees. These analyses suggest that varroa mites may be capable of modifying 7-dehydro-cholesterol precursor and hydroxylations of other steroid precursors, but whether the mites directly produce ecdysteroid precursors and products remains undetermined.

Employing Phylogenomics to Resolve the Relationships among Cnidarians, Ctenophores, Sponges, Placozoans, and Bilaterians

Despite an explosion in the amount of sequence data, phylogenomics has failed to settle controversy regarding some critical nodes on the animal tree of life. Understanding relationships among Bilateria, Ctenophora, Cnidaria, Placozoa, and Porifera is essential for studying how complex traits such as neurons, muscles, and gastrulation have evolved. Recent studies have cast doubt on the historical viewpoint that sponges are sister to all other animal lineages with recent studies recovering ctenophores as sister. However, the ctenophore-sister hypothesis has been criticized as unrealistic and caused by systematic error. We review past phylogenomic studies and potential causes of systematic error in an effort to identify areas that can be improved in future studies. Increased sampling of taxa, less missing data, and a priori removal of sequences and taxa that may cause systematic error in phylogenomic inference will likely be the most fruitful areas of focus when assembling future datasets. Ultimately, we foresee metazoan relationships being resolved with higher support in the near future, and we caution against dismissing novel hypotheses merely because they conflict with historical viewpoints of animal evolution.

Say goodbye to tribes in the new house fly classification: A new molecular phylogenetic analysis and an updated biogeographical narrative for the Muscidae (Diptera)

House flies are one of the best known groups of flies and comprise about 5000 species worldwide. Despite over a century of intensive taxonomic research on these flies, classification of the Muscidae is still poorly resolved. Here we brought together the most diverse molecular dataset ever examined for the Muscidae, with 142 species in 67 genera representing all tribes and all biogeographic regions. Four protein coding genes were analyzed: mitochondrial CO1 and nuclear AATS, CAD (region 4) and EF1-α. Maximum likelihood and Bayesian approaches were used to analyze five different partitioning schemes for the alignment. We also used Bayes factors to test monophyly of the traditionally accepted tribes and subfamilies. Most subfamilial taxa were not recovered in our analyses, and accordingly monophyly was rejected by Bayes factor tests. Our analysis consistently found three main clades of Muscidae and so we propose a new classification with only three subfamilies without tribes. Additionally, we provide the first timeframe for the diversification of all major lineages of house flies and examine contemporary biogeographic hypotheses in light of this timeframe. We conclude that the muscid radiation began in the Paleocene to Eocene and is congruent with the final stages of the breakup of Gondwana, which resulted in the complete separation of Antarctica, Australia, and South America. With this newly proposed classification and better understanding of the timing of evolutionary events, we provide new perspectives for integrating morphological and ecological evolutionary understanding of house flies, their taxonomy, phylogeny, and biogeography.