Metagenomic analysis of gut microbiome illuminates the mechanisms and evolution of lignocellulose degradation in mangrove herbivorous crabs.

BACKGROUND: Sesarmid crabs dominate mangrove habitats as the major primary consumers, which facilitates the trophic link and nutrient recycling in the ecosystem. Therefore, the adaptations and mechanisms of sesarmid crabs to herbivory are not only crucial to terrestrialization and its evolutionary success, but also to the healthy functioning of mangrove ecosystems. Although endogenous cellulase expressions were reported in crabs, it remains unknown if endogenous enzymes alone can complete the whole lignocellulolytic pathway, or if they also depend on the contribution from the intestinal microbiome. We attempt to investigate the role of gut symbiotic microbes of mangrove-feeding sesarmid crabs in plant digestion using a comparative metagenomic approach. RESULTS: Metagenomics analyses on 43 crab gut samples from 23 species of mangrove crabs with different dietary preferences revealed a wide coverage of 127 CAZy families and nine KOs targeting lignocellulose and their derivatives in all species analyzed, including predominantly carnivorous species, suggesting the crab gut microbiomes have lignocellulolytic capacity regardless of dietary preference. Microbial cellulase, hemicellulase and pectinase genes in herbivorous and detritivorous crabs were differentially more abundant when compared to omnivorous and carnivorous crabs, indicating the importance of gut symbionts in lignocellulose degradation and the enrichment of lignocellulolytic microbes in response to diet with higher lignocellulose content. Herbivorous and detritivorous crabs showed highly similar CAZyme composition despite dissimilarities in taxonomic profiles observed in both groups, suggesting a stronger selection force on gut microbiota by functional capacity than by taxonomy. The gut microbiota in herbivorous sesarmid crabs were also enriched with nitrogen reduction and fixation genes, implying possible roles of gut microbiota in supplementing nitrogen that is deficient in plant diet. CONCLUSIONS: Endosymbiotic microbes play an important role in lignocellulose degradation in most crab species. Their abundance is strongly correlated with dietary preference, and they are highly enriched in herbivorous sesarmids, thus enhancing their capacity in digesting mangrove leaves. Dietary preference is a stronger driver in determining the microbial CAZyme composition and taxonomic profile in the crab microbiome, resulting in functional redundancy of endosymbiotic microbes. Our results showed that crabs implement a mixed mode of digestion utilizing both endogenous and microbial enzymes in lignocellulose degradation, as observed in most of the more advanced herbivorous invertebrates.

Molecular phylogeny of deep-sea blind lobsters of the family Polychelidae (Decapoda: Polychelida), with implications for the origin and evolution of these "living fossils".

A comprehensive molecular analysis of the deep-sea blind lobsters of the family Polychelidae, often referred to as "living fossils", is conducted based on all six modern genera and 27 of the 38 extant species. Using six genetic markers from both mitochondrial and nuclear genomes, the molecular phylogenetic results differ considerably from previous morphological analyses and reveal the genera Polycheles and Pentacheles to be para- or polyphyletic. As the splitting of Polycheles has strong support from both molecular and morphological data, two new genera, Dianecheles and Neopolycheles, are erected for those species excluded from the clade containing the type species of Polycheles. The pattern of polyphyly of Pentacheles, however, is not robustly resolved, so it is retained as a single genus. Fossil evidence suggests that fossil polychelids inhabited deep-sea environments as early as the Early to Middle Jurassic, demonstrating the enduring adaptation of extant polychelid species to the deep-sea. Time-calibrated phylogeny suggested that modern polychelids probably had an Atlantic origin during the Jurassic period. Since their emergence, this ancient lobster group has continued to diversify, particularly in the West Pacific, and has colonized the abyssal zone, with the deepest genus, Willemoesia, representing the more 'derived' members among extant polychelids. Differences in eye reduction among extant polychelid genera highlight the necessity for ongoing investigations to ascertain the relative degree of functionality of their eyes, if they indeed retain any function.

Convergent adaptation of true crabs (Decapoda: Brachyura) to a gradient of terrestrial environments.

For much of terrestrial biodiversity, the evolutionary pathways of adaptation from marine ancestors are poorly understood, and have usually been viewed as a binary trait. True crabs, the decapod crustacean infraorder Brachyura, comprise over 7,600 species representing a striking diversity of morphology and ecology, including repeated adaptation to non-marine habitats. Here, we reconstruct the evolutionary history of Brachyura using new and published sequences of 10 genes for 344 tips spanning 88 of 109 brachyuran families. Using 36 newly vetted fossil calibrations, we infer that brachyurans most likely diverged in the Triassic, with family-level splits in the late Cretaceous and early Paleogene. By contrast, the root age is underestimated with automated sampling of 328 fossil occurrences explicitly incorporated into the tree prior, suggesting such models are a poor fit under heterogeneous fossil preservation. We apply recently defined trait-by-environment associations to classify a gradient of transitions from marine to terrestrial lifestyles. We estimate that crabs left the marine environment at least seven and up to 17 times convergently, and returned to the sea from non-marine environments at least twice. Although the most highly terrestrial- and many freshwater-adapted crabs are concentrated in Thoracotremata, Bayesian threshold models of ancestral state reconstruction fail to identify shifts to higher terrestrial grades due to the degree of underlying change required. Lineages throughout our tree inhabit intertidal and marginal marine environments, corroborating the inference that the early stages of terrestrial adaptation have a lower threshold to evolve. Our framework and extensive new fossil and natural history datasets will enable future comparisons of non-marine adaptation at the morphological and molecular level. Crabs provide an important window into the early processes of adaptation to novel environments, and different degrees of evolutionary constraint that might help predict these pathways.

Shift in symbiotic lifestyle as the major process shaping the evolution of pea crabs (Decapoda: Brachyura: Pinnotheroidea).

The pea crabs, superfamily Pinnotheroidea, are exceptional among brachyuran crabs in their diverse symbiotic associations involving both inquilinism and protective symbiosis. While this group presents a rare opportunity for evolutionary comparative study of host switching and morphological evolution in marine macroinvertebrates, previous phylogenetic studies have been focused on systematics. Here, we reconstructed the most extensive phylogeny of Pinnotheroidea based on two mitochondrial and six nuclear markers, with the aim of elucidating the host switching pathways and the correlation between symbiotic lifestyles and selected morphological adaptations. Ancestral state reconstruction of host association revealed a monophyletic origin of symbiosis in the form of inquilinism. Subsequent shifts in microhabitat preference for burrows or worm tubes, and the move to protective symbiosis, primarily in the switch to mollusc endosymbiosis, contributed to radiation in Pinnotheridae. Further parallel colonisations of echinoderms and tunicates occurred but did not lead to extensive diversification, except in the Clypeasterophilus + Dissodactylus lineage, which experienced a unique switch to echinoderm ectosymbiosis. The evolution of the third maxillipeds, carapace shape and ambulatory pereiopods suggests a rather strong coupling with the symbiotic lifestyle (whether inquilinism or protective symbiosis). Phenotypic diversity of these characters was higher among species engaged in protective symbiosis, with convergence in form (or function) among those sharing the same host affiliation. Species having different host affiliations or symbiotic lifestyles might also exhibit convergence in the form of the three morphological traits, suggesting a common adaptive value of the specialisations. Pinnotherid crabs overall exhibited a lower trait diversity than the also symbiotic palaemonid shrimps with comparable species diversity. This may plausibly be attributed to differences in potential for morphological modification to serve additional functions among the traits analysed in the two groups, the less frequent host switching and the less diverse host affiliations, and thus a less complicated evolutionary history in pinnotherids.

Recognition of Parapinnixidae Stevcic, 2005, and Tetriasidae fam. nov. in Pinnotheroidea De Haan, 1833 (Crustacea: Brachyura: Thoracotremata).

The systematic position of three aberrant pinnotheroid genera: Tetrias Rathbun, 1898, Parapinnixa Holmes, 1895 and Sakaina Serène, 1964, are reappraised. A new family, Tetriasidae fam. nov. is established for Tetrias, and Parapinnixidae Stevcic, 2005, is recognised for Parapinnixa and Sakaina. Tetriasids differ from all other pinnotheroids in that the articles of the palp of the third maxilliped (carpus, propodus and dactylus) are large and the dactylus is inserted at the distolateral corner of the propodus, whereas parapinnixids are distinctive in having the buccal cavern relatively small, subtriangular with the third maxilliped ischiomerus small, mesioproximally produced to form a triangular projection and is completely fused. The two families are phylogenetically distinct from the family Pinnotheridae based on the multi-locus gene tree, and are basal or near basal lineages in the Pinnotheroidea.

Molecular phylogeny of Thoracotremata crabs (Decapoda, Brachyura): Toward adopting monophyletic superfamilies, invasion history into terrestrial habitats and multiple origins of symbiosis.

The Thoracotremata is a large and successful group of "true" crabs (Decapoda, Brachyura, Eubrachyura) with a great diversity of lifestyles and well-known intertidal representatives. The group represents the largest brachyuran radiation into terrestrial and semi-terrestrial environments and comprises multiple lineages of obligate symbiotic species. In consequence, they exhibit very diverse physiological and morphological adaptations. Our understanding of their evolution is, however, largely obscured by their confused classification. Here, we resolve interfamilial relationships of Thoracotremata, using 10 molecular markers and exemplars from all nominal families in order to reconstruct the pathways of lifestyle transition and to prepare a new taxonomy corresponding to phylogenetic relationships. The results confirm the polyphyly of three superfamilies as currently defined (Grapsoidea, Ocypodoidea and Pinnotheroidea). At the family level, Dotillidae, Macrophthalmidae, and Varunidae are not monophyletic. Ancestral state reconstruction analyses and divergent time estimations indicate that the common ancestor of thoracotremes already thrived in intertidal environments in the Late Cretaceous and terrestrialization became a major driver of thoracotreme diversification. Multiple semi-terrestrial and terrestrial lineages originated and radiated in the Early Eocene, coinciding with the global warming event at the Paleocene-Eocene Thermal Maximum (PETM). Secondary invasions into subtidal regions and colonizations of freshwater habitats occurred independently through multiple semi-terrestrial and terrestrial lineages. Obligate symbiosis between thoracotremes and other marine macro-invertebrates evolved at least twice. On the basis of the current molecular phylogenetic hypothesis, it will be necessary in the future to revise and recognize seven monophyletic superfamilies and revisit the morphological character states which define them.

An Updated Checklist of Sea Slugs (Gastropoda, Heterobranchia) from Hong Kong Supported by Citizen Science.

Research on heterobranch sea slug diversity in Hong Kong was flourishing in the 1980-90s, with the first checklist and guidebook published and many new species and records documented later. This golden era of sea slug research ended abruptly, and no review nor any extensive collection has been done in the past 20+ years. In view of the extensive revision in heterobranch systematics in recent years, the current checklist can be considered out of date in both nomenclature and composition. Therefore, we are dedicated to providing a synthesis of the current state of knowledge on Hong Kong sea slug diversity by reviewing previous records and engagement of citizen science. An integration of previously published and unpublished records revealed the presence of 186 species, of which 107 species were documented by our citizen science programme with a further report of 71 new records. This yields a total of 257 species from 126 genera, 53 families and ten higher taxa, of which seven species have not been reported elsewhere from Hong Kong. While the present study has markedly illuminated our understanding of sea slug diversity in Hong Kong, the true biodiversity may be underestimated given the high proportion of novel records, especially when many previous records were not herein observed. Hong Kong likely harbours a greater sea slug diversity which awaits discovery from more rigorous sampling and a more inclusive citizen science programme.

Distinct suites of pre- and post-adaptations indicate independent evolutionary pathways of snapping claws in the shrimp family Alpheidae (Decapoda: Caridea).

One of the most notable evolutionary innovations of marine invertebrates is the snapping claw of alpheid shrimps (Alpheidae), capable of generating a powerful water jet and a shock wave, used for defense, aggression, excavation, and communication. Evolutionary analysis of this character complex requires the study of a suite of complementary traits to discern pre-adaptations or post-adaptations of snapping behavior. A comprehensive phylogenetic analysis of the Alpheidae based on two mitochondrial and four nuclear markers, covering 107 species from 38 genera (77.6% generic coverage), is presented. Ancestral state reconstruction analyses revealed five independent origins of snapping, two of which relate to the morphologically similar but phylogenetically distant genera Alpheus and Synalpheus, highlighting significant convergence. The evolution of the five complementary traits (adhesive plaques, tooth-cavity system, dactylar joint type, chela size enlargement, and orbital hood) did not always show a significant correlation with the evolution of snapping overall, sometimes only in a few lineages, suggesting different evolutionary pathways were involved and demonstrating the versatility in the evolution of the snapping mechanisms.

Evolution of protective symbiosis in palaemonid shrimps (Decapoda: Caridea) with emphases on host spectrum and morphological adaptations.

Palaemonidae is the most speciose caridean shrimp family, with its huge biodiversity partially generated via symbiosis with various marine invertebrates. Previous studies have provided insights into the evolution of protective symbiosis in this family with evidence for frequent inter-phyla host switches, but the comprehensiveness of evolutionary pathways is hampered by the resolution of the previous phylogenetic trees as well as the taxon coverage. Furthermore, several critical issues related to the evolution of a symbiotic lifestyle, including the change in host spectrum and corresponding morphological adaptations, remain largely unresolved. We therefore performed a much extended phylogenetic comparative study on Palaemonidae, rooted in a comprehensive phylogeny reconstructed by a supermatrix-supertree approach based on a total of three mitochondrial and five nuclear markers. Ancestral state reconstruction of host associations revealed at least three independent evolutions into symbiosis, with potentially a drive to seek protection fuelling incipient symbiosis. Yet, most of the observed symbiotic species diversity was radiated from a single cnidarian associate. The evolution of mandibles and ambulatory dactyli suggests a general lack of correlation with host affiliation (except sponge endosymbionts), implying limited morphological adaptations following host switching, despite being putatively a major adaptive consequence of symbiosis. Our analyses of host spectrum, in terms of basic and taxonomic specificity, revealed no apparent phylogenetic signal but instead resolved a dynamic pattern attributable to frequent host switching. Uncoupling between host spectrum and the degree of morphological specialisation is the norm in palaemonids, suggesting that morphological characters are not fully in tune with host spectrum, in addition to host affiliation. This study demonstrates the complexity in the evolution of symbiosis, pointing to the presence of cryptic adaptations determining host spectrum and governing host switch diversification, and provides a clear direction for the evolutionary study of symbiosis in other marine symbiotic groups involving host switching.

Fish and crustacean biodiversity in an outer maritime estuary of the Pearl River Delta revealed by environmental DNA.

Understanding the faunal community structure in the estuary would be crucial in assessing the health of the ecosystem. The poor visibility in the estuarine area due to the outflow from the Pearl River hinders the conventional visual census in assessing the megafaunal biodiversity. In this study, the fish and crustacean biodiversity of Hong Kong's western waters, i.e. the outer maritime estuary of the PRD, were studied through the metabarcoding of environmental DNA (eDNA). eDNA from the seawater and sediment samples was extracted from five sites in the region. After testing the performance of two genetic markers, amplicons of the cytochrome oxidase I, amplified by polymerase chain reaction, were subjected to Illumina high-throughput sequencing (MiSeq) analysis. A total of 22 fish species from 17 families and 34 crustacean species from 27 families were identified by blasting the sequences against the NCBI GenBank database, demonstrating segregation between samples from different sites. This study provides insight on the detail distribution of fish assembly in PRD, when compared with a previous eDNA study in the inner brackish PRD.

Insights into fungal diversity of a shallow-water hydrothermal vent field at Kueishan Island, Taiwan by culture-based and metabarcoding analyses.

This paper reports the diversity of fungi associated with substrates collected at a shallow hydrothermal vent field at Kueishan Island, Taiwan, using both culture-based and metabarcoding methods. Culture of fungi from yellow sediment (with visible sulfur granules), black sediment (no visible sulfur granules), the vent crab Xenograpsus testudinatus, seawater and, animal egg samples resulted in a total of 94 isolates. Species identification based on the internal transcribed spacer regions of the rDNA revealed that the yellow sediment samples had the highest species richness with 25 species, followed by the black sediment (23) and the crab (13). The Ascomycota was dominant over the Basidiomycota; the dominant orders were Agaricales, Capnodiales, Eurotiales, Hypocreales, Pleosporales, Polyporales and Xylariales. Hortaea werneckii was the only common fungus isolated from the crab, seawater, yellow and black sediment samples. The metabarcoding analysis amplifying a small fragment of the rDNA (from 18S to 5.8S) recovered 7-27 species from the black sediment and 12-27 species from the yellow sediment samples and all species belonged to the Ascomycota and the Basidiomycota. In the yellow sediments, the dominant order was Pleosporales and this order was also dominant in the black sediment together with Sporidiobolales. Based on the results from both methods, 54 and 49 species were found in the black and yellow sediments, respectively. Overall, a higher proportion of Ascomycota (~70%) over Basidiomycota was recovered in the yellow sediment and the two phyla were equally abundant in the black sediment. The top five dominant fungal orders in descending order based on species richness were Pleosporales>Eurotiales>Polyporales>Hypocreales>Capnodiales in the black sediment samples, and Polyporales>Pleosporales>Eurotiales>Capnodiales>Hypocreales in the yellow sediment samples. This study is the first to observe a high diversity of fungi associated with various substrates at a marine shallow water hydrothermal vent ecosystem. While some fungi found in this study were terrestrial species and their airborne spores might have been deposited into the marine sediment, several pathogenic fungi of animals, including Acremonium spp., Aspergillus spp., Fusarium spp., Malassezia spp., Hortaea werneckii, Parengyodontium album, and Westerdykella dispersa, were recovered suggesting that these fungi may be able to cause diseases of marine animals.

A highly diverse fungal community associated with leaves of the mangrove plant Acanthus ilicifolius var. xiamenensis revealed by isolation and metabarcoding analyses.

A high diversity of culturable foliar endophytic fungi is known from various mangrove plants, and the core taxa include species from Colletotrichum, Pestalotiopsis, Phoma, Phomopsis, Sporomiella, among others. Since a small fraction of fungi is able to grow in culture, this study investigated the diversity of fungi associated with leaves of Acanthus ilicifolius var. xiamenensis using both isolation and metabarcoding approaches. A total of 203 isolates were cultured from surface-sterilized leaves, representing 47 different fungal species: 30 species from the winter samples (104 isolates), and 26 species from the summer samples (99 isolates). Ascomycota was dominant in both types of leaf samples, while Basidiomycota was isolated only from the summer samples. Drechslera dematioidea (10.58%, percentage of occurrence), Colletotrichum sp. 3 (7.69%) and Alternaria sp. (7.69%) were dominant in the winter samples; Fusarium oxysporum (13.13%), Diaporthe endophytica (10.10%) and Colletotrichum sp. 1 (9.09%) in the summer samples. Overall, Corynespora cassiicola (6.90%), F. oxysporum (6.40%) and Guignardia sp. (6.40%) had the highest overall percentage of occurrence. In the metabarcoding analysis, a total of 111 operational taxonomic units (OTUs) were identified from 17 leaf samples: 96 OTUs from the winter and 70 OTUs from the summer samples. Sequences belonging to Ascomycota and Basidiomycota were detected in both samples but the former phylum was dominant over the latter. Based on read abundance, taxa having the highest percentage of occurrence included Alternaria sp. (3.46%), Cladosporium delicatulum (2.56%) and Pyrenochaetopsis leptospora (1.41%) in the winter leaves, and Aureobasidium sp. (10.72%), Cladosporium sp. (7.90%), C. delicatulum (3.45%) and Hortaea werneckii (3.21%) in the summer leaves. These latter four species also had the highest overall percentage of occurrence. Combining the results from both methods, a high diversity of fungi (at least 110 species) was found associated with leaves of A. ilicifolius var. xiamenensis. Many of the fungi identified were plant pathogens and may eventually cause diseases in the host.

Phylogenomic analyses of brachyuran crabs support early divergence of primary freshwater crabs.

Recent fossil calibrated molecular phylogenies have revealed that the Brachyura underwent rapid radiation during the Cretaceous and Early Tertiary, resulting in many early diverging lineages separated by short internodes that remain difficult to resolve. Here we present the first phylogenomic analyses of Brachyura using transcriptome data from 30 brachyuran species and 22 families. Analyses were carried out on a dataset containing 372 putative homologous loci (246,590 bps) and included data from 21 newly generated transcriptomes. With minor exceptions, all phylogenetic analyses recovered a congruent, highly resolved and well supported brachyuran phylogeny. Consistent with previous work, this phylogeny suggests that primary freshwater crabs diverged early in brachyuran evolution, falling sister to Thoracotremata, thus supporting recent proposal for establishment of subsection Potamoida for primary freshwater crabs. The interfamilial relationships among heterotremes were well resolved in our analyses but those within Thoracotremata remained problematic. Phylogenomic analyses clearly provide a powerful means for resolving brachyuran relationships, but future studies would benefit greatly from increased taxon sampling of transcriptome data.

CrusTF: a comprehensive resource of transcriptomes for evolutionary and functional studies of crustacean transcription factors.

BACKGROUND: Crustacea, the second largest subphylum of Arthropoda, includes species of major ecological and economic importance, such as crabs, lobsters, crayfishes, shrimps, and barnacles. With the rapid development of crustacean aquaculture and biodiversity loss, understanding the gene regulatory mechanisms of growth, reproduction, and development of crustaceans is crucial to both aquaculture development and biodiversity conservation of this group of organisms. In these biological processes, transcription factors (TFs) play a vital role in regulating gene expression. However, crustacean transcription factors are still largely unknown, because the lack of complete genome sequences of most crustacean species hampers the studies on their transcriptional regulation on a system-wide scale. Thus, the current TF databases derived from genome sequences contain TF information for only a few crustacean species and are insufficient to elucidate the transcriptional diversity of such a large animal group. RESULTS: Our database CrusTF ( http://qinlab.sls.cuhk.edu.hk/CrusTF ) provides comprehensive information for evolutionary and functional studies on the crustacean transcriptional regulatory system. CrusTF fills the knowledge gap of transcriptional regulation in crustaceans by exploring publicly available and newly sequenced transcriptomes of 170 crustacean species and identifying 131,941 TFs within 63 TF families. CrusTF features three categories of information: sequence, function, and evolution of crustacean TFs. The database enables searching, browsing and downloading of crustacean TF sequences. CrusTF infers DNA binding motifs of crustacean TFs, thus facilitating the users to predict potential downstream TF targets. The database also presents evolutionary analyses of crustacean TFs, which improve our understanding of the evolution of transcriptional regulatory systems in crustaceans. CONCLUSIONS: Given the importance of TF information in evolutionary and functional studies on transcriptional regulatory systems of crustaceans, this database will constitute a key resource for the research community of crustacean biology and evolutionary biology. Moreover, CrusTF serves as a model for the construction of TF database derived from transcriptome data. A similar approach could be applied to other groups of organisms, for which transcriptomes are more readily available than genomes.

Molecular phylogeny of Pasiphaeidae (Crustacea, Decapoda, Caridea) reveals systematic incongruence of the current classification.

Caridean shrimps constitute one of the most diverse groups of decapod crustaceans, notwithstanding their poorly resolved infraordinal relationships. One of the systematically controversial families in Caridea is the predominantly pelagic Pasiphaeidae, comprises 101 species in seven genera. Pasiphaeidae species exhibit high morphological disparity, as well as ecological niche width, inhabiting shallow to very deep waters (>4000m). The present work presents the first molecular phylogeny of the family, based on a combined dataset of six mitochondrial and nuclear gene markers (12S rDNA, 16S rDNA, histone 3, sodium-potassium ATPase α-subunit, enolase and ATP synthase ß-subunit) from 33 species belonged to six genera of Pasiphaeidae with 19 species from 12 other caridean families as outgroup taxa. Maximum likelihood and Bayesian inference analyses conducted on the concatenated dataset of 2265bp suggest the family Pasiphaeidae is not monophyletic, with Psathyrocaris more closely related to other carideans than to the other five pasiphaeid genera included in this analysis. Leptochela occupies a sister position to the remaining genera and is genetically quite distant from them. At the generic level, the analysis supports the monophyly of Pasiphaea, Leptochela and Psathyrocaris, while Eupasiphae is shown to be paraphyletic, closely related to Parapasiphae and Glyphus. The present molecular result strongly implies that certain morphological characters used in the present systematic delineation within Pasiphaeidae may not be synapomorphies and the classification within the family needs to be urgently revised.

A unique duplication of gene cluster (S2-C-Y) in Epopella plicata (Crustacea) mitochondrial genome and phylogeny within Cirripedia.

Barnacles (Crustacea: Cirripedia) are important model species in invertebrate larval biology, intertidal ecology, and anti-fouling researches. The complete mitochondrial genome of the intertidal barnacle Epopella plicata Gray, 1843 (Cirripedia: Sessilia: Tetraclitidae) is presented. The mitochondrial genome of E. plicata of 15 296 bp in length encodes 13 PCGs, 2 rRNA genes, and 25 tRNA genes. The genome of E. plicata has a duplicate gene cluster (trnS2-trnC-trnY) that is unique in the infraclass Cirripedia. The two copies of trnC share identical sequences, but nucleotide substitutions are observed in the other two pairs of tRNAs. Comparison of the two trnS2 indicates that DHU arm and acceptor stem have nucleotide variation. In the two trnY, nucleotide variations are found in the acceptor stem, TψC arm, DHU arm, and variable loop. However, there is no nucleotide variation in the anticodon arm of the three tRNAs. Epopella plicata mitochondrial genome shares seven gene rearrangements with that of Tetraclita japonica (Tetraclitidae), including trnK, trnA, trnE/trnS1, trnP/trnT, trnI/trnQ, trnY and trnC. Comparison of gene orders in the two tetraclitid barnacles and the pancrustacean ground pattern suggests that the arrangement of E. plicata mitochondrial genome is a derived character in this species within the family Tetraclitidae. Sequence analysis of all available barnacle mitochondrial genomes shows that within the order Sessilia, E. plicata and Tetraclita japonica cluster together, resulting in monophyly of Tetraclitidae. Notochthamalus scabrosus (Chthamalidae) is at the basal position of the order Sessilia. Monophyly of the family Balanidae was questioned based on both gene order comparison and sequence analyses, and its phylogenetic status needs to be elucidated further.

Multilocus approach reveals cryptic lineages in the goby Rhinogobius duospilus in Hong Kong streams: Role of paleodrainage systems in shaping marked population differentiation in a city.

Drainage history is a well-demonstrated factor that influences the population structure of freshwater inhabitants over a broad geographic scale. However, there has been little research undertaken on such a relationship with freshwater fish on a small geographical scale, especially in Asia. In this study, we investigated the role of local, small drainage systems in affecting the population genetic structure of a freshwater goby, Rhinogobius duospilus, in Hong Kong streams using a multilocus approach. Analyses on nine genetic markers (2 mitochondrial and 7 nuclear markers, including 5 microsatellite markers) reveal prominent and intensive genetic structuring (2.1-5.4% mtDNA sequence divergence) in R. duospilus in Hong Kong. The lineages and clusters recovered from mtDNA data and assignment analysis of nuclear markers coincide with the paleodrainage networks. Furthermore, marked population subdivision between streams located on different side branches (<20km apart) within the same paleodrainage area is observed and gene flow occurs only between closely situated streams that share common paleodrainage confluences. In an extreme case, gene flow is limited between streams that are less than 5km apart. Apparently, such an intensive population structure is attributed to the regional paleodrainage pattern, together with the highly sedentary life style of R. duospilus, which reduces contemporary gene flow and dispersal between populations in neighbouring streams.

Community Structure of Macrobiota and Environmental Parameters in Shallow Water Hydrothermal Vents off Kueishan Island, Taiwan.

Hydrothermal vents represent a unique habitat in the marine ecosystem characterized with high water temperature and toxic acidic chemistry. Vents are distributed at depths ranging from a few meters to several thousand meters. The biological communities of shallow-water vents have, however, been insufficiently studied in most biogeographic areas. We attempted to characterize the macrofauna and macroflora community inhabiting the shallow-water vents off Kueishan Island, Taiwan, to identify the main abiotic factors shaping the community structure and the species distribution. We determined that positively buoyant vent fluid exhibits a more pronounced negative impact to species on the surface water than on the bottom layer. Species richness increased with horizontal distance from the vent, and continuing for a distance of 2000 m, indicating that the vent fluid may exert a negative impact over several kilometers. The community structure off Kueishan Island displayed numerous transitions along the horizontal gradient, which were broadly congruent with changes in environmental conditions. Combination of variation in Ca2+, Cl-, temperature, pH and depth were revealed to show the strongest correlation with the change in benthic community structure, suggesting multiple factors of vent fluid were influencing the associated fauna. Only the vent crabs of Kueishan Island may have an obligated relationship with vents and inhabit the vent mouths because other fauna found nearby are opportunistic taxa that are more tolerant to acidic and toxic environments.

The complete mitochondrial genome of the fire coral-inhabiting barnacle Megabalanus ajax (Sessilia: Balanidae): gene rearrangements and atypical gene content.

The complete mitochondrial genome of Megabalanus ajax Darwin, 1854 (Sessilia: Balanidae) is reported. Compared to typical gene content of metazoan mitochondrial genomes, duplication of one tRNA gene (trnL2) and absence of another tRNA gene (trnS1) are identified in M. ajax mitochondrial genome. There is a replacement of one tRNA (trnS1) by another tRNA (trnL2) in M. ajax mitochondrial genome compared to Megabalanus volcano mitochondrial genome. Inversion of a six-gene block (trnP-nd4L-nd4-trnH-nd5-trnF) is found between M. ajax/M. volcano and Tetraclita japonica mitochondrial genomes. With reference to the pancrustacean mitochondrial ground pattern, there is an inversion of a large gene block from the light strand to heavy strand in the two Megabalanus mitochondrial genomes, including three PCGs and two tRNAs (nd4L-nd4-trnH-nd5-trnF). Furthermore, four tRNAs (trnA, trnE, trnQ and trnC) exhibit translocation, while translocation and inversion occur in three tRNAs (trnP, trnY and trnK).

The mitochondrial genome of Nobia grandis Sowerby, 1839 (Cirripedia: Sessilia): the first report from the coral-inhabiting barnacles family Pyrgomatidae.

This work presents the coral-inhabiting barnacle Nobia grandis Sowerby, 1839 complete mitochondrial genome, which is the first report from the family Pyrgomatidae (Cirripedia: Sessilia). The N. grandis mitochondrial genome is 15,032 bp in length, containing a total of 469 bp of non-coding nucleotides spreading in 11 intergenic regions (with the largest region of 376 bp). Compared with the pancrustacean ground pattern, there are not less than seven tRNAs rearranged in the N. grandis mitochondrial genome. Gene overlaps are founded in eight places. Nine PCGs (COX1-3, ATP6, ATP8, CYTB, ND2, ND3 and ND6) are encoded on the heavy strand while the remaining 4 PCGs and the two rRNAs are located on the light strand. As the first representative from the family Pyrgomatidae, the N. grandis mitochondrial genome will help us to explore the evolutionary history and molecular evolution of coral barnacles and Sessilia in future studies.