Kimura 2-parameter Distances Research Articles

Cryptic diversity in the pen shell Atrina pectinata (Bivalvia: Pinnidae): high divergence and hybridization revealed by molecular and morphological data

Cryptic species have been increasingly revealed in the marine realm through an analytical approach incorporating multiple lines of evidence (e.g., mtDNA, nuclear genes and morphology). Illustrations of cryptic taxa improve our understanding of species diversity and evolutionary histories within marine animals. The pen shell Atrina pectinata is known to exhibit extensive morphological variations that may harbour cryptic diversity. In this study, we investigated A. pectinata populations along the coast of China and one from Japan to explore possible cryptic diversity and hybridization using a combination of mitochondrial (cytochrome c oxidase subunit I, mtCOI) and nuclear (ribosomal internal transcribed spacer, nrITS) genes as well as morphology. Phylogenetic analyses of mtCOI 'DNA barcoding gene' sequences resolved six divergent lineages with intralineage divergences between 0.4% and 0.8%. Interlineage sequence differences ranged from 4.3% to 22.0%, suggesting that six candidate cryptic species are present. The nrITS gene revealed five deep lineages with Kimura 2-parameter distances of 3.7-30.3%. The five nuclear lineages generally corresponded to mtCOI lineages 1-4 and (5+6), suggestive of five distinct evolutionary lineages. Multiple nrITS sequences of significant variance were found within an individual, clearly implying recent hybridization events between/among the evolutionary lineages, which contributed to cytonuclear discordance. Morphologically, five morphotypes matched the five genetic lineages, although the intermediates may well blur the boundaries of different morphotypes. This study demonstrates the importance of combining multiple lines of evidence to explore species cryptic diversity and past evolutionary histories.

COI is better than 16S rRNA for DNA barcoding Asiatic salamanders (Amphibia: Caudata: Hynobiidae)

The 5' region of the mitochondrial DNA (mtDNA) gene cytochrome c oxidase I (COI) is the standard marker for DNA barcoding. However, because COI tends to be highly variable in amphibians, sequencing is often challenging. Consequently, another mtDNA gene, 16S rRNA gene, is often advocated for amphibian barcoding. Herein, we directly compare the usefulness of COI and 16S in discriminating species of hynobiid salamanders using 130 individuals. Species identification and classification of these animals, which are endemic to Asia, are often based on morphology only. Analysis of Kimura 2-parameter genetic distances (K2P) documents the mean intraspecific variation for COI and 16S rRNA genes to be 1.4% and 0.3%, respectively. Whereas COI can always identify species, sometimes 16S cannot. Intra- and interspecific genetic divergences occasionally overlap in both markers, thus reducing the value of a barcoding gap to identify genera. Regardless, COI is the better DNA barcoding marker for hynobiids. In addition to the comparison of two potential markers, high levels of intraspecific divergence in COI (>5%) suggest that both Onychodactylus fischeri and Salamandrella keyserlingii might be composites of cryptic species.

DNA barcoding of fishes of Laguna de Bay, Philippines

Laguna de Bay, the largest lake in the Philippines, is an important part of the country's fisheries industry. It is also home to a number of endemic fishes including Gobiopterus lacustris (Herre 1927) of family Gobiidae, Leiopotherapon plumbeus (Kner 1864) of family Terapontidae, Zenarchopterus philippinus (Peters 1868) of family Hemiramphidae and Arius manillensis Valenciennes 1840 of family Ariidae. Over the years, a steady decline has been observed in the abundance and diversity of native fishes in the lake due to anthropogenic disturbances. In this study, a total of 71 specimens of 18 different species belonging to 18 genera, 16 families, and seven orders were DNA barcoded using the mitochondrial cytochrome c oxidase subunit I (COI) gene. All of the fish species were discriminated by their COI sequences and one endemic species G. lacustris, showing deep genetic divergence, was highlighted for further taxonomic investigation. Average Kimura 2-parameter genetic distances within species, family, and order were 1.33%, 18.91%, and 24.22%, respectively. These values show that COI divergence increases as taxa become less exclusive. All of the COI sequences obtained were grouped together according to their species designation in the Neighbor-joining tree that was constructed. This study demonstrated that DNA barcoding has great potential as a tool for fast and accurate species identification and also for highlighting species that warrant further taxonomic investigation.

Endemic Angiostrongyliasis, Rio de Janeiro, Brazil

Endemic Angiostrongyliasis, Rio de Janeiro, Brazil

Establishment of a mitochondrial DNA sequence database for the identification of fish species commercially available in South Africa

The limitations intrinsic to morphology-based identification systems have created an urgent need for reliable genetic methods that enable the unequivocal recognition of fish species, particularly those that are prone to overexploitation and/or market substitution. The aim of this study was to develop a comprehensive reference library of DNA sequence data to allow the explicit identification of 53 commercially available fish species in South Africa, most of which were locally caught marine species. Sequences of approximately 655 base pairs were generated for all species from the cytochrome c oxidase I (COI) gene, the region widely adopted for DNA barcoding. Specimens of the genus Thunnus were examined in further detail, employing additional mitochondrial DNA control region sequencing. Cumulative analysis of the sequences from the COI region revealed mean conspecific, congeneric and confamilial Kimura 2-parameter distances of 0.10%, 4.58% and 15.43%, respectively. The results showed that the vast majority (98%) of fish species examined could be readily differentiated by their COI barcodes, but that supplementary control region sequencing was more useful for the discrimination of three Thunnus species. Additionally, the analysis of COI data raised the prospect that Thyrsites atun (snoek) could constitute a species pair. The present study has established the necessary genetic information to permit the unambiguous identification of 53 commonly marketed fish species in South Africa, the applications of which hold a plethora of benefits relating to ecology research, fisheries management and control of commercial practices.

Barcode haplotype variation in north American agroecosystem lady beetles (Coleoptera: Coccinellidae)

DNA barcodes have proven invaluable in identifying and distinguishing insect pests, most notably for determining the provenance of exotic invasives, but relatively few insect natural enemies have been barcoded. We used Folmer etal.'s (1994) universal invertebrate primers and Hebert etal.'s (2004) for Lepidoptera, to amplify 658 bp at the 5' end of the mitochondrial cytochrome oxidase c subunit I (COI) gene in five species of lady beetles from crop fields in six states in the US Mid-Atlantic, Plains and Midwest: three native species, Hippodamia convergens Guérin-Méneville, H.parenthesis (Say) and Coleomegilla maculata (De Geer); and two exotic species, Harmonia axyridis (Pallas) and Coccinella septempunctata Linnaeus. Sequence divergences within species were low, never exceeding 0.9% (Kimura 2-parameter distances). Sequence divergences between the two Hippodamia species ranged from 14.7 to 16.4%, mirroring the relationships found for other arthropod taxa. Among the exotic species, C.septempunctata sequences were as variable as those of the three native species, while H.axyridis populations comprised a single haplotype. Limited data on two Coleomegilla subspecies, C.m.lengi Timberlake and C.m.fuscilabris (Mulsant), are consistent with their belonging to the same species, although morphological and reproductive data indicate that they represent separate species. Our results support the general utility of COI barcodes for distinguishing and diagnosing coccinellid species, but point to possible limitations in the use of barcodes to resolve species assignments in recently divergent sibling species.

DNA barcoding of the ichthyofauna of Taal Lake, Philippines

This study represents the first molecular survey of the ichthyofauna of Taal Lake and the first DNA barcoding attempt in Philippine fishes. Taal Lake, the third largest lake in the Philippines, is considered a very important fisheries resource and is home to the world's only freshwater sardine, Sardinella tawilis. However, overexploitation and introduction of exotic fishes have caused a massive decline in the diversity of native species as well as in overall productivity of the lake. In this study, 118 individuals of 23 native, endemic and introduced fishes of Taal Lake were barcoded using the partial DNA sequence of the mitochondrial cytochrome c oxidase subunit I (COI) gene. These species belong to 21 genera, 17 families and 9 orders. Divergence of sequences within and between species was determined using Kimura 2-parameter (K2P) distance model, and a neighbour-joining tree was generated with 1000 bootstrap replications using the K2P model. All COI sequences for each of the 23 species were clearly discriminated among genera. The average within species, within genus, within family and within order percent genetic divergence was 0.60%, 11.07%, 17.67% and 24.08%, respectively. Our results provide evidence that COI DNA barcodes are effective for the rapid and accurate identification of fishes and for identifying certain species that need further taxonomic investigation.

Cytochrome c oxidase subunit 1 barcode data of fish of the Nayband National Park in the Persian Gulf and analysis using meta‐data flag several cryptic species

We provide cytochrome c oxidase subunit 1 (COI) barcode sequences of fishes of the Nayband National Park, Persian Gulf, Iran. Industrial activities, ecological considerations and goals of The Fish Barcode of Life campaign make it crucial that fish species residing in the park be identified. To the best of our knowledge, this is the first report of barcoding data on fishes of the Persian Gulf. We examined 187 individuals representing 76 species, 56 genera and 32 families. The data flagged potentially cryptic species of Gerres filamentosus and Plectorhinchus schotaf. 16S rDNA data on these species are provided. Exclusion of these two potential cryptic species resulted in a mean COI intraspecific distance of 0.18%, and a mean inter- to intraspecific divergence ratio of 66.7. There was no overlap between maximum Kimura 2-parameter distances among conspecifics (1.66%) and minimum distance among congeneric species (6.19%). Barcodes shared among species were not observed. Neighbour-joining analysis showed that most species formed cohesive sequence units with little variation. Finally, the comparison of 16 selected species from this study with meta-data of conspecifics from Australia, India, China and South Africa revealed high interregion divergences and potential existence of six cryptic species. Pairwise interregional comparisons were more informative than global divergence assessments with regard to detection of cryptic variation. Our analysis exemplifies optimal use of the expanding barcode data now becoming available.

DNA Barcoding the Medusozoa using mtCOI

The Medusozoa are a clade within the Cnidaria comprising the classes Hydrozoa, Scyphozoa, and Cubozoa. Identification of medusozoan species is challenging, even for taxonomic experts, due to their fragile forms and complex, morphologically-distinct life history stages. In this study 231 sequences for a portion of the mitochondrial Cytochrome Oxidase I (mtCOI) gene were obtained from 95 species of Medusozoans including; 84 hydrozoans (61 siphonophores, eight anthomedusae, four leptomedusae, seven trachymedusae, and four narcomedusae), 10 scyphozoans (three coronatae, four semaeostomae, two rhizostomae, and one stauromedusae), and one cubozoan. This region of mtCOI has been used as a DNA barcode (i.e., a molecular character for species recognition and discrimination) for a diverse array of taxa, including some Cnidaria. Kimura 2-parameter (K2P) genetic distances between sequence variants within species ranged from 0 to 0.057 (mean 0.013). Within the 13 genera for which multiple species were available, K2P distance between congeneric species ranged from 0.056 to 0.381. A cluster diagram generated by Neighbor Joining (NJ) using K2P distances reliably clustered all barcodes of the same species with ≥99% bootstrap support, ensuring accurate identification of species. Intra- and inter-specific variation of the mtCOI gene for the Medusozoa are appropriate for this gene to be used as a DNA barcode for species-level identification, but not for phylogenetic analysis or taxonomic classification of unknown sequences at higher taxonomic levels. This study provides a set of molecular tools that can be used to address questions of speciation, biodiversity, life-history, and population boundaries in the Medusozoa.

DNA barcoding of fungi: a case study using ITS sequences for identifying aquatic hyphomycete species

Aquatic hyphomycetes are a polyphyletic group of fungi that play a crucial role in organic matter turnover in streams. They have been traditionally identified based on the morphology of conidia collected in stream water or obtained from leaves colonized in nature upon aeration in the laboratory. Therefore, species identification is limited by our ability to induce conidium production and to establish pure cultures. Conidial shapes are believed to be the result of convergent evolution, so similar conidia may be produced by different conidiogenesis processes, which may prevent unambiguous identification. Currently, a great effort in fungal taxonomy is being made at introducing a set of criteria based on comparisons of selected nucleotide sequences instead of or in addition to phenotypic characters. We examined the suitability of ITS1-5.8S-ITS2 rRNA gene region or its subregions (ITS1 and ITS2) to identify aquatic hyphomycetes, by sequencing and comparing these regions in 94 fungal isolates belonging to 19 species collected in Portuguese streams with different environmental conditions during 8 years. Sequences of ITS1, ITS2 and ITS1-5.8S-ITS2 rRNA genes of the Portuguese isolates of aquatic hyphomycetes and those from the GenBank exhibited taxonomic cohesiveness, the isolates grouped with their respective species but all Tricladium species did not group within the Tricladium genus. Cohesiveness was not observed between isolates with respect to location, condition of stream or date of collection. Evolutionary divergences (ITS1-5.8S-ITS2 sequences; Kimura 2-parameter distance) between con-specific isolates were shallow and a deep divergence between species was generally observed. The NJ trees based on ITS1 or ITS2 rRNA gene sequences had lower statistical support for some internal nodes, we therefore propose ITS1-5.8S-ITS2 rRNA gene as barcode for identifying species of aquatic hyphomycetes.

DNA barcoding provides distinction between Radix Astragali and its adulterants

Based on variable nuclear and/or organellar DNA sequences among vastly divergent species as well as morphologically indistinguishable species, DNA barcoding is widely applicable in species identification, biodiversity studies, forensic analyses, and authentication of medicinal plants. The roots of Astragalus membranaceus and A. membranaceus var. mongholica are commonly used as Radix Astragali in several Asian countries, including China, Japan, and Korea. However, in addition to the two species recorded in the Chinese Pharmacopoeia, there are twenty-three species from different genera including Astragalus, Oxytropis, Hedysarum, and Glycyrrhiza, which have been used as adulterants not only in trading markets but also by the herbal medicine industry. Therefore, a simple, reliable, and accurate classification method is important for distinguishing authentic Radix Astragali from its adulterants. In this study, we acquired data for 37 samples from four related genera within the family Fabaceae. Then we compared four candidate DNA barcoding markers using ITS, matK, rbcL, and coxI sequences from nuclear, chloroplast, and mitochondrial genomes, all commonly used for plants to identify genetic variations among genera, intraspecies, and interspecies. We observed higher divergences among genera and interspecies for ITS, which have the average Kimura 2-parameter distances of 4.5% and 14.1%, respectively, whereas matK was found to have sufficient divergence at the intraspecific level. Moreover, two indels detected in the matK sequence are useful for PCR studies in distinguishing Radix Astragali from its adulterants. This study suggests that the combined barcoding regions of ITS and matK are superior barcodes for Radix Astragali and further studies should focus on evaluating the applicability and accuracy of such combined markers for a wide range of traditional Chinese herbs.

DNA barcoding of Cuban freshwater fishes: evidence for cryptic species and taxonomic conflicts

Despite ongoing efforts to protect species and ecosystems in Cuba, habitat degradation, overuse and introduction of alien species have posed serious challenges to native freshwater fish species. In spite of the accumulated knowledge on the systematics of this freshwater ichthyofauna, recent results suggested that we are far from having a complete picture of the Cuban freshwater fish diversity. It is estimated that 40% of freshwater Cuban fish are endemic; however, this number may be even higher. Partial sequences (652 bp) of the mitochondrial gene COI (cytochrome c oxidase subunit I) were used to barcode 126 individuals, representing 27 taxonomically recognized species in 17 genera and 10 families. Analysis was based on Kimura 2-parameter genetic distances, and for four genera a character-based analysis (population aggregation analysis) was also used. The mean conspecific, congeneric and confamiliar genetic distances were 0.6%, 9.1% and 20.2% respectively. Molecular species identification was in concordance with current taxonomical classification in 96.4% of cases, and based on the neighbour-joining trees, in all but one instance, members of a given genera clustered within the same clade. Within the genus Gambusia, genetic divergence analysis suggests that there may be at least four cryptic species. In contrast, low genetic divergence and a lack of diagnostic sites suggest that Rivulus insulaepinorum may be conspecific with Rivulus cylindraceus. Distance and character-based analysis were completely concordant, suggesting that they complement species identification. Overall, the results evidenced the usefulness of the DNA barcodes for cataloguing Cuban freshwater fish species and for identifying those groups that deserve further taxonomic attention.

Are the Proposed env Mutations Actually Associated With Resistance to Maraviroc?

Are the Proposed env Mutations Actually Associated With Resistance to Maraviroc?

Comparison of Ribosomal DNA ITS Regions Among Hippophae rhamnoides ssp. sinensis from Different Geographic Areas in China

Hippophae rhamnoides ssp. sinensis is of ecological and practical importance, PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of the rDNA ITS region was conducted to estimate the genetic diversity of H. rhamnoides ssp. sinensis at 19 sites in Northern China. Restriction analysis divided the samples into seven RFLP patterns (I–VII), which implied that H. rhamnoides ssp. sinensis had a degree of genetic diversity. The genetic diversity of H. rhamnoides ssp. sinensis mainly lied within populations other than among populations, and the results also suggested that geographic distances did not have any clear effect on their genetic differentiation. The sequences of rDNA ITS region varied in length from 656 to 658 bp, which exhibited 95–100% sequence identity. Pairwise Kimura 2-parameter distances within these H. rhamnoides ssp. sinensis samples ranged from 0.27% to 5.95%. There were 48 variable sites within the entire ITS region, among them transitions were more frequent than transversions. The ITS1 and ITS2 transcripts of H. rhamnoides ssp. sinensis had conserved secondary structures, implying that the ITS region maybe under evolutionary pressure to maintain the RNA secondary structure involved in the post-transcriptional processing of rRNA.

Mitochondrial lineages and DNA barcoding of closely related species in the mayfly genus Ephemerella (Ephemeroptera:Ephemerellidae)

AbstractWe compared genetic lineages in the mayfly genus Ephemerella (Ephemeroptera:Ephemerellidae) identified from mitochondrial DNA (mtDNA) to current taxonomy in 9 morphological taxa, including 2 geographically widespread species, Ephemerella invaria ( = E. inconstans, E. rotunda, E. floripara) and Ephemerella dorothea ( = E. infrequens). Maximum likelihood and parsimony analyses of the mtDNA sequences placed E. inconstans and E. invaria in a well-supported clade; however, mean Kimura 2-parameter genetic distance between the lineages was high (5.2%) relative to distance within lineages (1.3%). The phylogenetic relationships of synonyms E. rotunda and E. floripara were not resolved, but estimates of mean genetic distance to E. invaria were high for both (8.5% and 11.6%, respectively). Populations of E. dorothea were grouped in 2 well-supported clades (12.9% mean divergence) that did not include the synonym E. infrequens (20.9% mean divergence, based on a single sample). A large genetic distance (18.6%) ...

DNA barcoding of stylommatophoran land snails: a test of existing sequences

DNA barcoding has attracted attention because it is a potentially simple and universal method for taxonomic assignment. One anticipated problem in applying the method to stylommatophoran land snails is that they frequently exhibit extreme divergence of mitochondrial DNA sequences, sometimes reaching 30% within species. We therefore trialled the utility of barcodes in identifying land snails, by analysing the stylommatophoran cytochrome oxidase subunit I sequences from GenBank. Two alignments of 381 and 228 base pairs were used to determine potential error rates among a test data set of 97 or 127 species, respectively. Identification success rates using neighbour-joining phylogenies were 92% for the longer sequence and 82% for the shorter sequence, indicating that a high degree of mitochondrial variation may actually be an advantage when using phylogeny-based methods for barcoding. There was, however, a large overlap between intra- and interspecific variation, with assignment failure (per cent of samples not placed with correct species) particularly associated with a low degree of mitochondrial variation (Kimura 2-parameter distance<0.05) and a small GenBank sample size (<25 per species). Thus, while the optimum intra/interspecific threshold value was 4%, this was associated with an overall error of 32% for the longer sequences and 44% for the shorter sequences. The high error rate necessitates that barcoding of land snails is a potentially useful method to discriminate species of land snail, but only when a baseline has first been established using conventional taxonomy and sample DNA sequences. There is no evidence for a barcoding gap, ruling out species discovery based on a threshold value alone.

Genetic Analysis of the Flagella Gene of Lyme Disease Spirochetes ( Borrelia burgdorferi) Isolated from the Offshore Kinmen Island of Taiwan

The flagella gene of Lyme disease spirochetes (Borrelia burgdorferi) was analyzed for the first time in Taiwan. The genetic identities of these Taiwan isolates (TWKM17) were clarified by comparing their sequence similarities and nucleotide distance values of the PCR-amplified flagella genes with three major genospecies of Lyme disease spirochetes for human infection and other zoonotic species of Borrelia spirochetes. Results from 26 isolates indicate that the sequence similarity of these Taiwan isolates revealed a highly homogeneous genotype, ranging from 99.3% to 100%, within the genospecies of B. burgdorferi sensu stricto and was distinguished from other genospecies of Borrelia isolates. Moreover, the nucleotide distance values performed by a pairwise distance calculation (Kimura 2-parameter distance) revealed a highly homogeneity ( 0.05) among other genospecies of spirochetes. The phylogenetic analysis also demonstrated that all these Taiwan isolates were closely related to the genospecies of B. burgdorferi sensu stricto within the same phylogenic group of B. burgdorferi sensu lato and can be clearly distinguished from other zoonotic species of Borrelia isolates. Thus, we conclude that all these Taiwan isolates should be classified into the genospecies of B. burgdorferi sensu stricto based on the genetic identity of the flagella gene.

New evidence on the systematic and phylogenetic position of Parides burchellanus (Lepidoptera: Papilionidae)

Parides burchellanus is considered a rare and threatened swallowtail species restricted to central Brazil. It shows considerable morphological similarity to Parides panthonus jaguarae, with which it shares both geographical range and larval host plant. At present, P. burchellanus and P. panthonus are believed to be distinct species, based on minor differences in male genitalia. In this study, the phylogenetic and systematic position of P. burchellanus in relation to three subspecies of P. panthonus (P. p. jaguarae, P. p. lysimachus and P. p. aglaope) was evaluated using molecular evidence: the complete sequence of the mtDNA genes COI and COII and of the nuclear gene EF-1α (c. 3300bp). In addition, the informativeness of the 'barcode' region next to the 5' end of COI (c. 650bp) was evaluated for delimiting these taxa. Individual analysis by neighbour-joining, using Kimura 2-parameter distance model, and by maximum parsimony showed that P. p. jaguarae+P.p. lysimachus+P. p. aglaope+P. burchellanus form a strongly supported monophyletic clade, and all molecular regions consistently recovered P. p. jaguarae and P. burchellanus as sister species. The genetic divergence among the subspecies of P. panthonus and P. burchellanus is equivalent to the divergence among conspecifics of other species of Parides, and smaller than the interspecific divergence among different sister species of this genus. The results support the proposal that P. p. jaguarae and P. burchellanus are likely to be synonymous, and suggest that P. burchellanus can be considered conspecific with P. panthonus. The taxonomic classification of P. burchellanus should be revised on the basis of the molecular data.

若尔盖湿地青海沙蜥红原亚种线粒体ND4-tRNA leu 基因的序列变异和遗传多样性

According to the distribution of Phrynocephalus vlangalii hongyuanensis in Zoige Wetland，three geographic units: Zoige Xiaman (XM)，Hongyuan (HY)，both in Sichuan Province and Maqu (MQ) in Gansu Province were defined. We used molecular methods to reveal these unit’s genetic variation and diversity. A 785bp fragment of the mtDNA ND4-tRNAleu was determined from 72 samp1es in seven populations of P. vlangalii hongyuanensis. Seven variable nucleotide sites and nine haplotypes were identified in the 785bp fragments. As a whole，the haplotype diversity was high (0.806±0.024)，but the nucleotide diversity was low (0.00231±0.00016). In a single population，MQa，MQb and XMb had very low genetic diversities，and XMc had a much higher one. The Kimura 2-parameter distances among all the populations were small (0.001-0.005)，and the distance between MQa and XMa was the greatest. Analysis of molecular variance (AMOVA) showed that the three units were distinctly different (P<0.01)，and 62.61% of the total genetic diversity was attributable to variation among units. There were 3 haplotypes shared among XM and HY，and no geographic clustering was observed except MQ from the TCS network. The results from the mismatch distribution analysis and Fu’s Fs test (Fs=－2.21937) implied that there might be a recent population expansion in the XM unit，and this may be the reason why XM had a high haplotype diversity but a low nucleotide diversity. We estimate that the MQ and XMb have lower diversities because of some very recent geographic events，such as the formation of the Yellow river’s upriver and the Zoige Wetland. Although they are distinctly different，not enough time has passed for them to have diverged a great genetic distance.

Genetic differentiation in the genus Uroconger in the Indo-Pacific region

Only a few species of congrid eels of the genus Uroconger (Congridae) have been described worldwide, but between these species each of the adult and larval morphologies are very similar. U. lepturus is the only species currently recognized in the Indo-Pacific, however, previous morphological counts of the total myomeres of Uroconger leptocephali suggest that more than 1 spe- cies may occur in this region. In this study, 1222 sites of the mitochondrial 16S rRNA gene were deter- mined from 54 Uroconger leptocephali and one adult U. lepturus collected from 2 different regions of the Indo-Pacific to examine their genetic differentiations. The neighbor-joining tree based on Kimura's 2-parameter distances showed 4 major groups among the specimens examined, including one with the U. lepturus adult. The average inter-group genetic distances were 0.0348 to 0.0648, almost 20 times greater than the intra-group distances (0.0028 to 0.0036), and the former were larger than the distances between species in some other eels, such as those of the genera Conger and Anguilla. No clear geographic differentiation was found, but a highly significant difference was found between the 2 closest sister Groups A and B (FST = 0.90062, p < 0.05). However, the key char- acters of both the total number of myomeres and the position of the last vertical blood vessel over- lapped among the genetic groups. These findings suggest the possibility of the presence of cryptic lineages within the genus Uroconger in the Indo-Pacific region.