Genetic differentiation between populations of swimming crab <Emphasis Type="Italic">Portunus trituberculatus</Emphasis> along the coastal waters of the East China Sea

Portunus trituberculatus is a commercially important species widely spread in the East China Sea. Intraspecific variation of the mitochondrial DNA cytochrome oxidase subunit I (mtDNA COI) gene was investigated in 213 individuals from six localities (Changjiang Estuary, Shengsi Islands, Zhoushan Islands, Dongtou Islands, Dinghai Bay, and Quanzhou Bay) ranging from north (31°21′N) to south (24°55′N) coastal waters of the East China Sea. Overall, a total of 27 mtDNA haplotypes and 21 variable sites were detected in the 787 bp segment of COI gene. Analysis of mtDNA COI sequence data revealed that crabs from the six localities were characterized by moderately high haplotypic diversity (h = 0.787 ± 0.026), while sequence divergence values between haplotypes were relatively low (π = 0.00241 ± 0.00098). Each population was characterized by a single most frequent haplotype, shared among all six localities, and a small number of rare ones, typically present in only one or two individuals and representative of a specific population. However, neither the neighbor-joining tree nor the minimum spanning network (MSN) based on the haplotype data exhibited geographical patterns of the six populations. Mismatch distribution analysis of P. trituberculatus individuals sampled from the six localities suggested that sudden population expansion might have occurred in CJ and SS population that might be consistent with over-exploitation of the swimming crab. Analysis of molecular variance (AMOVA) and F _ST statistics showed that significant genetic differentiation existed among the SS, ZS, DT, DH, and QZ populations, suggesting that gene flow might be reduced, even between the geographically close sites, despite the high potential of dispersal. The possible causes of the observed genetic heterogeneity among the P. trituberculatus populations and the potential applications of the mtDNA COI marker in the artificial breeding and fisheries management are discussed. Handling editor: C. Sturmbauer     

Escaping introns in COI through cDNA barcoding of mushrooms: Pleurotus as a test case

DNA barcoding involves the use of one or more short, standardized DNA fragments for the rapid identification of species. A 648‐bp segment near the 5′ terminus of the mitochondrial cytochrome c oxidase subunit I (COI) gene has been adopted as the universal DNA barcode for members of the animal kingdom, but its utility in mushrooms is complicated by the frequent occurrence of large introns. As a consequence, ITS has been adopted as the standard DNA barcode marker for mushrooms despite several shortcomings. This study employed newly designed primers coupled with cDNA analysis to examine COI sequence diversity in six species of Pleurotus and compared these results with those for ITS. The ability of the COI gene to discriminate six species of Pleurotus, the commonly cultivated oyster mushroom, was examined by analysis of cDNA. The amplification success, sequence variation within and among species, and the ability to design effective primers was tested. We compared ITS sequences to their COI cDNA counterparts for all isolates. ITS discriminated between all six species, but some sequence results were uninterpretable, because of length variation among ITS copies. By comparison, a complete COI sequences were recovered from all but three individuals of Pleurotus giganteus where only the 5′ region was obtained. The COI sequences permitted the resolution of all species when partial data was excluded for P. giganteus. Our results suggest that COI can be a useful barcode marker for mushrooms when cDNA analysis is adopted, permitting identifications in cases where ITS cannot be recovered or where it offers higher resolution when fresh tissue is. The suitability of this approach remains to be confirmed for other mushrooms.     

Mitochondrial DNA diversity of <Emphasis Type="Italic">Cleruchoides noackae</Emphasis> (Hymenoptera: Mymaridae): a potential biological control agent for <Emphasis Type="Italic">Thaumastocoris peregrinus</Emphasis> (Hemiptera: Thaumastocoridae)

Thaumastocoris peregrinus Carpintero and Dellapé (Hemiptera: Thaumastocoridae) is a native Australian Eucalyptus sap-feeding insect that has become invasive and seriously damaging to commercially grown Eucalyptus in the Southern Hemisphere. Cleruchoides noackae Lin and Huber (Hymenoptera: Mymaridae) was recently discovered as an egg parasitoid of the Thaumastocoridae in Australia. Mitochondrial DNA (mtDNA; cytochrome c oxidase subunit I, COI) sequence diversity amongst 104 individuals from these native C. noackae populations revealed 24 sequence haplotypes. The COI haplotypes of individuals collected from the Sydney and Southeast Queensland clustered in distinct groups, indicating limited spread of the insect between the regions. Individuals collected from Perth in Western Australia were represented by four COI haplotypes. Although this population is geographically more isolated from other populations, two COI haplotypes were identical to haplotypes found in the Sydney region. The results suggest that C. noackae has recently been introduced into Perth, possibly from the Sydney area. The high mtDNA diversity and limited spread that is suggested for C. noackae is in contrast to the lack of geographic associated mtDNA diversity and extensive spread of T. peregrinus. If implemented as a biological control agent, this factor will need to be considered in collecting and releasing C. noackae.     

BIODIVERSITY RESEARCH: Genetic diversity in two introduced biofouling amphipods (Ampithoe valida & Jassa marmorata) along the Pacific North American coast: investigation into molecular identification and cryptic diversity

Aim We investigated patterns of genetic diversity among invasive populations of Ampithoe valida and Jassa marmorata from the Pacific North American coast to assess the accuracy of morphological identification and determine whether or not cryptic diversity and multiple introductions contribute to the contemporary distribution of these species in the region. Location Native range: Atlantic North American coast; Invaded range: Pacific North American coast. Methods We assessed indices of genetic diversity based on DNA sequence data from the mitochondrial cytochrome c oxidase subunit I (COI) gene, determined the distribution of COI haplotypes among populations in both the invasive and putative native ranges of A. valida and J. marmorata and reconstructed phylogenetic relationships among COI haplotypes using both maximum parsimony and Bayesian approaches. Results Phylogenetic inference indicates that inaccurate species‐level identifications by morphological criteria are common among Jassa specimens. In addition, our data reveal the presence of three well supported but previously unrecognized clades of A. valida among specimens in the north‐eastern Pacific. Different species of Jassa and different genetic lineages of Ampithoe exhibit striking disparity in geographic distribution across the region as well as substantial differences in genetic diversity indices. Main conclusions Molecular genetic methods greatly improve the accuracy and resolution of identifications for invasive benthic marine amphipods at the species level and below. Our data suggest that multiple cryptic introductions of Ampithoe have occurred in the north‐eastern Pacific and highlight uncertainty regarding the origin and invasion histories of both Jassa and Ampithoe species. Additional morphological and genetic analyses are necessary to clarify the taxonomy and native biogeography of both amphipod genera.     

Barcoding,population structure,and demographic history of Prodiplosis longifila associated with the Andes

Prodiplosis longifila Gagné (Diptera: Cecidomyiidae) is an insect pest that attacks various types of crops, including tomato, Solanum lycopersicum L. (Solanaceae), a vegetable with substantial economic significance worldwide. Prodiplosis longifila is a widely distributed pest in Colombia, Ecuador, and Peru, countries characterized by the presence of significant geographic barriers like the Andes Mountains. It has been reported that geographic barriers affect the dynamics and genetic differentiation of insect populations. Therefore, the aim of this study was to assess the diversity, genetic structure, and demographic history of P. longifila through the analysis of sequences within the mitochondrial region of cytochrome oxidase I (COI) and rDNA‐ITS2 in 27 populations located in Colombia and Ecuador. Analyses were performed on populations distributed in three geographic groups separated by the presence of the Andes Mountains. A total of 11 haplotypes were identified with the COI gene and only one haplotype in the rDNA‐ITS2 was found. Analyses of population structure and demographic history revealed that there is a structure associated with the Andes, which is reflected in an uneven distribution of the haplotype frequencies between regions, but even so, gene flow between populations was detected which produces low genetic differentiation. Because P. longifila has a short‐range dispersion that determines its territorial nature, it would be expected that other factors are producing the genetic exchange between populations. We suggest that the anthropogenic effect produced by farming practices, such as the use of seedlings as seed, which may carry P. longifila larvae, cause passive dispersal of pest throughout the Andes, particularly in Colombia.     

Phylogeography of Hyalomma (Euhyalomma) lusitanicum (Acarina,Parasitiformes, Ixodidae) in Andalusia based on mitochondrial cytochrome oxidase I gene

The genetic population structure relationships of Hyalomma (Euhyalomma) lusitanicum in Andalusia (the south of the Iberian Peninsula) were examined using mtDNA sequence data from 887 bp of cytochrome oxidase subunit I (COI) gene. The sequence for the COI region was determined for 84 individuals collected in several localities of Andalusia, and 10 for other localities (i.e., five from Toledo, central Iberian Peninsula, four from Sicily (Italy) and one from Canary Island). Seventeen haplotypes were detected, including 27 polymorphic sites. The number of amino acid substitutions per site from mean diversity calculations for the entire population was 0.017. AMOVA analysis revealed a low gene flow that characterises the genetic population structure of this species in South Iberian Peninsula, with a haplotype diversity (h) value of 0.815. No geographically induced differentiation was observed, and separate evolutionary units were not detected. Our results indicate low genetic diversity across the geographical range of H. lusitanicum tick in Andalusia. Our data do not show any genetic discontinuity between the tick populations studied, including specimens from Canary Island and Sicily (Italy).

     

Genetic divergence between the South Korean and Mongolian populations of the dung beetle,Gymnopleurus mopsus (Coleoptera: Scarabaeidae) based on mitochondrial cytochrome c oxidase subunit I (COI) gene sequences

The locally extinct dung beetle, Gymnopleurus mopsus Pallas, 1781 (Coleoptera: Scarabaeidae), has not been found in South Korea since the 1970s. This research was conducted to understand the genetic divergence between the South Korean and Mongolian populations of G. mopsus as a part of its reintroduction program in South Korea. The genetic distance and diversity were determined using the mitochondrial cytochrome c oxidase subunit I (COI) gene sequence (658 bp ) corresponding to the DNA barcode region. The mitochondrial COI gene sequences of 64 individuals of G. mopsus collected in South Korea (7 individuals) and Mongolia (57 individuals) showed a relatively high level of genetic diversity (nucleotide diversity, 0.0078 ± 0.0007; Haplotype diversity, 0.965 ± 0.017). The genetic distances between the South Korean and Mongolian populations lay within the intraspecific level and the phylogenetic reconstruction using the neighbor‐joining (NJ) method showed that all individuals belonged to a single clade. This result indicates that the current Mongolian population of G. mopsus is a good candidate source population to restore the locally extinct population of the species in South Korea.     

Low genetic diversity and lack of genetic structure in the giant jellyfish Nemopilema nomurai in Chinese coastal waters

The giant jellyfish Nemopilema nomurai is a scyphozoan species well-known in East Asian Marginal Seas for its damage to fisheries. The genetic diversity and population structure of N. nomurai, collected from five geographic regions in Chinese coastal seas, were examined based on mitochondrial cytochrome c oxidase subunit I (COI) gene and nuclear internal transcribed spacer one (ITS1) sequences. A total of 26 and five unique haplotypes were recovered from the COI and ITS1 genes, respectively. The overall genetic diversity of N. nomurai calculated by the COI and ITS1 sequences was low (haplotype diversity 0.727% and 0.108%, nucleotide diversity 0.212% and 0.039%). The median-joining network analysis revealed a star-like haplotype network. The hierarchical Analysis of Molecular Variance (AMOVA) of COI haplotypes showed that N. nomurai populations form a single population, with a low F_ST (0.0149, p?=?0.1036). The dispersal ability, together with the biological characteristics, could be important factors for the lack of a geographically structured pattern in N. nomurai in Chinese coastal waters.     

Diversity in the genus Rhabdias (Nematoda,Rhabdiasidae): Evidence for cryptic speciation

Lungworms from the genus Rhabdias are common parasites of amphibians and reptiles distributed worldwide. To assess the diversity of Rhabdias spp., we performed molecular analyses of 35 specimens sampled in different regions of Brazil. Molecular analyses were based on the internal transcribed spacer (ITS), large subunit (28S) ribosomal and the cytochrome oxidase I (COI) mitochondrial genes. DNA sequence divergence was compared among ribosomal and mitochondrial genes, analyses using the general mixed Yule‐coalescent (GMYC) method based on the COI gene were used to identify possible cryptic diversity, and phylogenetic analyses using concatenated ITS and 28S ribosomal genes were used to test the monophyly of Rhabdiasidae. We revealed five morphospecies: R. cf. stenocephala, R. breviensis, R. pseudosphaerocephala and two new species, Rhabdias sp.4 and Rhabdias sp.5. DNA sequence levels of divergence among genes ITS, 28S and COI were compared, and the efficiency of the molecular markers to identify species (ITS and COI) and lineages (COI) was tested. GMYC was assigned to 17 well‐supported clades (i.e., 17 species), and cryptic diversity was detected in the Neotropical region as evidenced by the multiple lineages in R. breviensis and R. pseudosphaerocephala. In addition, our results suggest evidence for host–parasite cophylogeny in the R. pseudosphaerocephala complex and dispersal events among their populations. Phylogenetic analyses supported the monophyly of Rhabdiasidae and improved the resolution of main clades. Rhabdias breviensis is closely related to Rhabdias cf. africanus, Rhabdias cf. stenocephala, R. pseudosphaerocephala, Rhabdias sp.4 and Rhabdias sp.5 grouping together in a main clade with Neotropical‐related species. The large geographical distribution appeared to be a phylogenetic pattern among the species of Rhabdias from the neotropics.     

Genetic variation of the hawthorn spider mite Amphitetranychus viennensis (Acari: Tetranychidae) in Korea

Amphitetranychus viennensis (Zacher) is a serious economic pest of various fruit trees. Due to its restricted geographic distribution in Asia and Europe, it is an important quarantine species in the North American countries. Despite its significance in agricultural damage and quarantine, the genetic diversity of this species has not been studied in detail. In this study, we determined the nucleotide sequences of mitochondrial cytochrome c oxidase subunit I (COI) gene and internal transcribed spacer 2 (ITS2) region of the nuclear ribosomal DNA in A. viennensis collected from various regions of Korea. Variations in the COI and ITS2 sequences of the Korean samples ranged up to 6.92 and 4.02 %, respectively. A sequence comparison showed that the Korean samples were divided into two groups, one comprising the Geoje and Jinju samples, and the other comprising all samples except for the Geoje/Jinju samples. In most samples, except for the Geoje/Jinju samples, variations in both COI and ITS2 sequences were less than 1.04 and 0.99 %, respectively. However, the variations between two groups were 6.23–6.92 % and 3.02–4.02 %, respectively. In addition, the phylogenic analysis performed with sequences in the GenBank database showed that the samples from Geoje/Jinju, which are located in the southern region of Korea, were most similar to the Japanese samples, but the others were most similar to those of China and Taiwan. Thus, our study suggests that two genetically different groups of A. viennensis exist in Korea.     

Range edges and the molecular divergence of Greya moth populations

Aim We investigated the geographical pattern of genetic divergence and demographic history in the prodoxid moth Greya obscura throughout its entire geographical range in far western North America and compared it to the geographical patterns found in a previously studied species, Greya politella, which co‐occurs over the same range, in the same habitats, and on the same host plants. Location The study included sites distributed throughout the California Floristic Province. Methods We used analysis of cytochrome c oxidase subunit I (COI) and amplified fragment length polymorphisms to evaluate the pattern and history of genetic continuity among populations. Results Greya obscura populations show a history of spatial expansion with considerable haplotype diversity in the centre of the geographical range. As with G. politella, some range‐edge populations of G. obscura are sufficiently divergent (6.7% in COI) to be considered as potentially cryptic species. Greya obscura and G. politella, however, differ in the specific range‐edge sites showing greatest genetic divergence and cryptic speciation. Main conclusions These results corroborate the view that range edges are important cradles of divergence and speciation. In addition, the results indicate that the geographical pattern of divergence at edges may differ even among closely related species occupying the same habitats and using the same hosts.     

Population genetic structure and intraspecific genetic distance of Periplaneta americana (Blattodea: Blattidae) based on mitochondrial and nuclear DNA markers

The American cockroach (Periplaneta americana) is a globally invasive pest that can cause significant economic loss and threaten human health. Although it is abundant and lives in close proximity to humans, few studies have investigated the genetic diversity of P. americana. Our study analyzed 1,053 P. americana and other Periplaneta species' samples from different locations in China and the United States. A traditional tree‐based method using 17 unique mitochondrial COI haplotypes of P. americana and 20 haplotypes of the other Periplaneta species accurately identified P. americana with a barcoding threshold of 5.1%. To identify the population genetic structure of P. americana, we investigated wingless gene and pooled them with obtained mtDNA data for a combined analysis. Although the genetic diversity of the USA group was relatively higher than the China group, the number of haplotypes and alleles of both groups was small. The analysis of molecular variance (AMOVA), intraspecific phylogeny, and haplotype networks indicated that P. americana had very little global genetic differentiation. The weak geographic genetic structure might reflect the human‐mediated dispersal of P. americana. Despite no apparent phylogeographic assignment of mtDNA and nuclear lineages was observed in both BI trees, the integrated COI sequence data identified four distinct P. americana haplotype groups, showing four ancient maternal lineages of P. americana in China and the United States.     

DNA barcoding and evaluation of genetic diversity in Cyprinidae fish in the midstream of the Yangtze River

The Yangtze River is the longest river in China and is divided into upstream and mid‐downstream regions by the Three Gorges (the natural barriers of the Yangtze River), resulting in a complex distribution of fish. Dramatic changes to habitat environments may ultimately threaten fish survival; thus, it is necessary to evaluate the genetic diversity and propose protective measures. Species identification is the most significant task in many fields of biological research and in conservation efforts. DNA barcoding, which constitutes the analysis of a short fragment of the mitochondrial cytochrome c oxidase subunit I (COI) sequence, has been widely used for species identification. In this study, we collected 561 COI barcode sequences from 35 fish from the midstream of the Yangtze River. The intraspecific distances of all species were below 2% (with the exception of Acheilognathus macropterus and Hemibarbus maculatus). Nevertheless, all species could be unambiguously identified from the trees, barcoding gaps and taxonomic resolution ratio values. Furthermore, the COI barcode diversity was found to be low (≤0.5%), with the exception of H. maculatus (0.87%), A. macropterus (2.02%) and Saurogobio dabryi (0.82%). No or few shared haplotypes were detected between the upstream and downstream populations for ten species with overall nucleotide diversities greater than 0.00%, which indicated the likelihood of significant population genetic structuring. Our analyses indicated that DNA barcoding is an effective tool for the identification of cyprinidae fish in the midstream of the Yangtze River. It is vital that some protective measures be taken immediately because of the low COI barcode diversity.     

Assessing the genetic diversity and population structure of Culter alburnus in China based on mitochondrial 16S rRNA and COI gene sequences

The genetic diversity and population genetic structure of Culter alburnus were investigated using mitochondrial cytochrome c oxidase subunit I (COI) and ribosomal 16S subunit (16S rRNA) gene sequences. A total of 89 individuals from four localities were included in the analysis. Overall, 12 polymorphic sites were observed and 10 haplotypes were defined. The C. alburnus populations were characterized by high haplotype diversity (0.587 ± 0.047) and low nucleotide diversity (0.00197 ± 0.00073). Pairwise fixation index (F_ST) analysis indicated significant genetic differentiation among different populations. The hierarchical analysis of molecular variance (AMOVA) analysis also showed significant genetic divergence (φ_ST = 0.3792, P < 0.01) among these populations. The present results suggest that subdivisions exist among four C. alburnus populations, and should be considered as different management unit for effective conservation and management purposes. This study provides new information for genetic assessment and will be crucial for establishing fisheries management and strategies for this species.     

不同地理种群银杏大蚕蛾COI基因序列变异与遗传分化

银杏大蚕蛾Caligula japonica是亚洲东部的特有种, 既是一种重要的林业害虫, 也是一种珍贵的野生蚕类资源。为了揭示银杏大蚕蛾地理种群间的内在联系, 测定了我国分布的12个地理种群的线粒体细胞色素氧化酶C亚基I（COI）基因部分序列（GenBank登录号: FJ358506-FJ358517）, 对地理种群间的序列变异和遗传分化进行了分析。结果表明: 银杏大蚕蛾地理种群间的COI序列同源性高达99%~100%, 显示出比较小的遗传差异。序列对准后从供试COI序列中仅鉴定出9个变异位点和6个单元型, 其中3种是共享单元型。系统发育分析结果表明种群间已经按地理位置形成了一定的地理格局, AMOVA分析显示北方组和南方组之间已经具有明显的遗传分化（FST=0.478, P<0.001）。综合分析, 我们认为北方组和南方组之间的遗传分化可能与差异巨大的生态条件有关。研究结果为银杏大蚕蛾的种群遗传学和生态学研究提供了一个基本的分子生物学线索。     

Genetic diversity and population connectivity of the Asian green mussel Perna viridis in South China Sea,inferred from mitochondria DNA markers

The Asian green mussel Perna viridis is ecologically and economically important in the coastal regions of China. In order to characterize the genetic diversity and population connectivity of P. viridis in South China Sea, a 664 bp region of mitochondrial COI gene and a 293 bp region of 16S rRNA gene were sequenced and analyzed for 78 and 92 individuals from four populations in South China Sea, respectively. A total of 15 haplotypes were defined by 14 variable nucleotide sites in COI gene, and 7 haplotypes by 6 variable nucleotide sites in 16S rRNA gene. High haplotype diversity and low nucleotide diversity were observed in COI gene, while moderate haplotype diversity and low nucleotide diversity were observed in 16S rRNA gene. Pairwise F_ST values of COI gene were all negative and those of 16S rRNA gene ranged from −0.01409 to 0.10289. The results showed that no significant genetic divergence (or shallow genetic structure) and high levels of population connectivity among the four populations of P. viridis in South China Sea.     

Potential speciation of morphotypes in the photosymbiotic ascidian <Emphasis Type="Italic">Didemnum molle</Emphasis> in the Ryukyu Archipelago,Japan

Four morphotypes are recognized in the photosymbiotic ascidian Didemnum molle in the Ryukyu Archipelago: three color morphs (white, dark gray, and brown) of small-type colonies and one large-type colony (white with gray patches). The genetic variation among these four morphotypes was investigated by constructing phylogenetic trees based on a 401-bp fragment of the cytochrome oxidase subunit I (COI) gene of 29 specimens collected from five islands (Okinawajima, Sesokojima, Ikeijima, Kumejima, and Ishigakijima). The results support the monophyly of the genus Didemnum and that of the four morphotypes of D. molle. Moreover, the phylogenetic trees discriminated four clades corresponding to each morphotype. The geographic differences of the sequences were much smaller than the differences among the morphotypes, suggesting that the four morphotypes in D. molle are discrete sibling species. Communicated by Biology Editor Dr Ruth Gates     

Variation in mitochondrial cytochrome c oxidase subunit I gene in Nezara viridula (Hemiptera: Pentatomidae) from Argentina

Here, we examine the genetic diversity in the agricultural pest Nezara viridula (Linnaeus, 1758 ) from populations of Argentina using mitochondrial cytochrome c oxidase subunit I (COI) gene sequences. The DNA sequence comparisons of 718 base pairs of the COI gene revealed seven haplotypes. The observed total haplotype diversity (Hd) value was of 0.138, and the nucleotide diversity was of 0.00039 and 0.00135 according to π and θ_W, respectively. Eight out of the 10 populations analysed, mostly from soya bean crops, only presented the more frequent haplotype, while 2 haplotypes were found in a mixed culture and 6 haplotypes in a peanut culture. Factors such as differential insecticide applications, as well as the surrounding habitat, and the host plant preference could be related to the genetic diversity differences observed among samples of N. viridula. The analysis of genetic diversity in samples collected in crops treated and non‐treated with insecticides, as well as in samples collected from different seasons, could help to clarify the role of the factors that led to the pattern of genetic diversity detected in this study. The result of a comparative analysis of COI gene sequences among populations from South America, Africa, Asia and Europe was consistent with the hypothesis of an African origin of N. viridula. On the other hand, the haplotypes of Europe were clustered with haplotypes from South America. In addition, specimens from Madeira (west of Europe) shared ancestry with South America and Europe. It has been suggested that a probable route of colonization of America could have been from Western Europe towards the eastern coasts of South America.     

Mitochondrial DNA (COI) analyses reveal that amphipod diversity is associated with environmental heterogeneity in deep‐sea habitats

The relationship between species diversity and environmental parameters is poorly understood for the mobile macrofauna of deep‐sea habitats due to under‐sampling and subsequent lack of accurate taxonomic information. To redress this, cytochrome oxidase c subunit I (COI) DNA sequences were used to estimate species diversity and to compare phoxocephalid amphipod assemblages among 20 stations encompassing a range of environmental conditions. Two regions, east (Chatham Rise) and west (Challenger Plateau) of New Zealand were sampled to depths of 200–1200 m with an epibenthic sled. Using a comparison among identified morphospecies, we found a clear gap in sequence divergences between 6% and 13% and used a 6% threshold to designate molecular operational taxonomic units (MOTUs), as a surrogate to putative species. DNA sequences (n = 297) revealed high total diversity (n = 49 MOTUs), as well as high beta diversity (28 MOTUs found at single location only). Novel phoxocephalid MOTUs were found at most stations, especially on Challenger Plateau and the flanks of Chatham Rise. Analyses of interstation assemblages revealed a major split between regions, indicating minimal overlap in taxon distributions. A cluster of highly similar stations was identified, broadly distributed over the crest of Chatham Rise, in association with elevated food availability, probably resulting from higher surface productivity and relatively shallow depth. Accordingly, multivariate analysis revealed a strong correlation between phoxocephalid assemblages and food supply. This study highlights the value of molecular approaches, in particular COI sequences, for quantifying and comparing diversity in under‐sampled and/or under‐studied taxa.     

Genetic population structure of miiuy croaker (Miichthys miiuy) in the Yellow and East China Seas base on mitochondrial COI sequences

The miiuy croaker (Miichthys miiuy) is an economically important fish species in China. However, information about population structure in this species is limited. In this study, the genetic diversity and population structure of four populations of Miichthys miiuy were investigated using a mitochondrial DNA (mtDNA) cytochrome c oxidase subunit I (COI) segment of 599 bp. A total of 35 polymorphic sites, and 31 haplotypes were defined in 109 individuals. High levels of haplotype diversity (0.731 ± 0.047) and low nucleotide diversity (0.00278 ± 0.0019) were observed in miiuy croaker populations. The results of AMOVA and pairwise fixation index (F_ST) analysis did not indicate any significant genetic differentiation among populations obtained from four sites (P > 0.05). In addition, no significant genealogical branches or clusters were recognized in the NJ tree. Analysis of neutral evolution and mismatch distribution suggested that the miiuy croaker might have experienced a recent population expansion.