Phylogenetic relationships and the evolution of regulatory gene sequences in the parrotfishes

Regulatory genes control the expression of other genes and are key components of developmental processes such as segmentation and embryonic construction of the skull in vertebrates. Here we examine the variability and evolution of three vertebrate regulatory genes, addressing issues of their utility for phylogenetics and comparing the rates of genetic change seen in regulatory loci to the rates seen in other genes in the parrotfishes. The parrotfishes are a diverse group of colorful fishes from coral reefs and seagrasses worldwide and have been placed phylogenetically within the family Labridae. We tested phylogenetic hypotheses among the parrotfishes, with a focus on the genera Chlorurus and Scarus, by analyzing eight gene fragments for 42 parrotfishes and eight outgroup species. We sequenced mitochondrial 12s rRNA (967 bp), 16s rRNA (577 bp), and cytochrome b (477 bp). From the nuclear genome, we sequenced part of the protein-coding genes rag2 (715 bp), tmo4c4 (485 bp), and the developmental regulatory genes otx1 (672 bp), bmp4 (488bp), and dlx2 (522 bp). Bayesian, likelihood, and parsimony analyses of the resulting 4903 bp of DNA sequence produced similar topologies that confirm the monophyly of the scarines and provide a phylogeny at the species level for portions of the genera Scarus and Chlorurus. Four major clades of Scarus were recovered, with three distributed in the Indo-Pacific and one containing Caribbean/Atlantic taxa. Molecular rates suggest a Miocene origin of the parrotfishes (22 mya) and a recent divergence of species within Scarus and Chlorurus, within the past 5 million years. Developmentally important genes made a significant contribution to phylogenetic structure, and rates of genetic evolution were high in bmp4, similar to other coding nuclear genes, but low in otx1 and the dlx2 exons. Synonymous and non-synonymous substitution patterns in developmental regulatory genes support the hypothesis of stabilizing selection during the history of these genes, with several phylogenetic regions of accelerated non-synonymous change detected in the phylogeny.     

Evolution of mouthbrooding and life-history correlates in the fighting fish genus Betta

The origin of and evolutionary transitions among the extraordinary diverse forms of parental care in teleost fish remain largely unknown. The "safe harbor" hypothesis predicts that the evolution from a "guarding" to a "brooding" form of care in teleost fish is associated with shifts in reproductive and life-history features such as reduced fecundity, and increased egg volume with higher parental investment. Robust phylogenetic hypotheses may help to identify evolutionary changes in key traits associated with differences in the form of parental care. Here, we used reconstruction of ancestral character states to study the evolution of the two forms of parental care, bubble nesting and mouthbrooding in the fighting fish genus Betta. We also applied a comparative analysis using the phylogenetic generalized least-squares method to test the "safe harbor" hypothesis by evaluating differences between the two forms of parental care in standard length, life-history traits, and three habitat variables. Evolutionary hypotheses were derived from the first molecular phylogeny (nuclear and mitochondrial DNA sequence data; 4448 bp) of this speciose group. Ancestral character state reconstructions of the evolution of the form of parental care in the genus Betta, using the methods of unweighted parsimony and maximum likelihood, are uncertain and further indicate a high rate of evolutionary transitions. Applying different weights for the suspected directionality of changes, based on the consistent phenotypic and behavioral differences found between bubble nesters and mouthbrooders, recurrent origin of mouthbrooding in the genus Betta is favored using parsimony. Our comparative analyses further demonstrate that bubble nesters and mouthbrooders do not have a consistent set of life-history correlates. The form of parental care in Betta is correlated only with offspring size, with mouthbrooders having significantly bigger offspring than bubble nesters, but is not correlated with egg volume, clutch size, and broodcare duration, nor with any of the three habitat variables tested. Our results thus challenge the general predictions of the "safe harbor" hypothesis for the evolution of alternative brood care forms in the fighting fish genus Betta.     

Molecular phylogenetics and ecological diversification of the transisthmian fish genus Centropomus (Perciformes: Centropomidae).

Phylogenetic relationships among the 12 recognized fish species in the New World genus Centropomus (Pisces, Centropomidae) were analyzed using allozyme electrophoresis and 618 bp of the mitochondrial DNA 16S ribosomal RNA (rRNA) gene. Molecular phylogenetic trees were generally consistent with previously published partial hypotheses based on morphological evidence. However, previously undefined sister group relationships between major species groups were resolved using molecular data, and phylogenetic hypotheses for Centropomus based on 16S rRNA sequences were better supported than were allozyme-based hypotheses. The high level of congruence among the trees inferred from the nuclear and mitochondrial characters provided a firm phylogenetic basis for analysis of ecological diversification and molecular evolution in the genus. Compared to basal Centropomus species, members of the most nested species group were significantly larger in body size and occupied a marine niche only peripherally utilized by their congeners. We also observed substitution rate heterogeneity among 16S rRNA lineages; in contrast to expectations based on "metabolic rate" and "generation interval" models, relative substitution rates were faster than expected for the group of large-bodied snooks. Using the Pliocene rise of the Central American isthmian marine barrier to calibrate rates of 16S ribosomal gene evolution in Centropomus, we found that the rates for the genus were similar to those reported for higher vertebrates. Analysis of the three sets of transisthmian geminate taxa in Centropomus indicated that two of the pairs were probably formed during the Pliocene rise of the isthmus while the third pair diverged several million years earlier.     

Phylogenetic perspectives in the evolution of parental care in ray-finned fishes

Among major vertebrate groups, ray-finned fishes (Actinopterygii) collectively display a nearly unrivaled diversity of parental care activities. This fact, coupled with a growing body of phylogenetic data for Actinopterygii, makes these fishes a logical model system for analyzing the evolutionary histories of alternative parental care modes and associated reproductive behaviors. From an extensive literature review, we constructed a supertree for ray-finned fishes and used its phylogenetic topology to investigate the evolution of several key reproductive states including type of parental care (maternal, paternal, or biparental), internal versus external fertilization, internal versus external gestation, nest construction behavior, and presence versus absence of sexual dichromatism (as an indicator of sexual selection). Using a comparative phylogenetic approach, we critically evaluate several hypotheses regarding evolutionary pathways toward parental care. Results from maximum parsimony reconstructions indicate that all forms of parental care, including paternal, biparental, and maternal (both external and internal to the female reproductive tract) have arisen repeatedly and independently during ray-finned fish evolution. The most common evolutionary transitions were from external fertilization directly to paternal care and from external fertilization to maternal care via the intermediate step of internal fertilization. We also used maximum likelihood phylogenetic methods to test for statistical correlations and contingencies in the evolution of pairs of reproductive traits. Sexual dichromatism and nest construction proved to be positively correlated with the evolution of male parental care in species with external fertilization. Sexual dichromatism was also positively correlated with female-internal fertilization and gestation. No clear indication emerged that female-only care or biparental care were evolutionary outgrowths of male-only care, or that biparental care has been a common evolutionary stepping stone between paternal and maternal care. Results are discussed in the context of prior thought about the evolution of alternative parental care modes in vertebrates.     

Molecular phylogeny and systematics of the pseudoxyrhophiine snake genus Liopholidophis (Reptilia, Colubridae): evolution of its exceptional sexual dimorphism and descriptions of new taxa

The pseudoxyrhophiine snake genus Liopholidophis Mocquard, 1904 is endemic to Madagascar and consists of two distinct species groups. We performed molecular phylogenetic analyses using nucleotide sequences of c . 2200 bp from two mitochondrial genes (16S rRNA, cyt b ) and one nuclear gene (c-mos) to test the monophyly of the genus Liopholidophis and to investigate the relationships of the known species and an unidentified Liopholidophis population. Our phylogeny strongly supports the polyphyly of the genus Liopholidophis , confirms the monophyly of both species groups, and reveals that the unidentified population belongs to a new species. We therefore transfer the species of the former L. stumpffi group ( L. epistibes , L. infrasignatus , L. lateralis , L. martae , and L. stumpffi ) to a new genus Bibilava gen. n. and describe Liopholidophis dimorphus sp. n. from the rainforests of Montagne d'Ambre National Park in northern Madagascar. Finally, we compare our phylogeny with previous hypotheses and discuss the evolution of the extreme sexual dimorphism in tail length of Liopholidophis s. str.     

Evolutionary transitions in parental care in cichlid fish

Cichlid fishes (Cichlidae) are well suited for testing theories of the evolution of vertebrate parental care. These freshwater teleost fish provide parental care for their offspring, display many different forms of care and have interspecific variation in which sex stays with the young. Here, we assemble the first family-wide composite phylogeny based on morphological and molecular studies, and trace two sets of character evolution: form of care (substrate guarding and mouthbrooding), and sex of care-giver (biparental, female-only, and male-only). Mouthbrooding has evolved from ancestral substrate guarding with 10 to 14 transitions and 0 to 3 reversals. The data support hypothesized transitions in the sex of care-giver, with uniparental female care having arisen from biparental care 21 to 30 times with 0 to 10 reversals. There is also evidence that male-only care evolved once from biparental care. These transitions in parental care characters are the most numerous reported for any family of vertebrates and, to our knowledge, provide the first quantitative support for models of parental care evolution in fish.     

Molecular phylogeny and evolutionary habitat transition of the flower bugs (Heteroptera: Anthocoridae)

We performed a molecular phylogenetic study of the Anthocoridae, the flower bugs, based on maximum likelihood, maximum parsimony, and Bayesian analyses of ～ 3000 base pairs (bp) of DNA sequence from the mitochondrial 16S rRNA and nuclear 18S rRNA and 28S rRNA genes for 44 taxa. Our phylogenetic analyses indicates that (i) the tribe Cardiastethini (Dufouriellini) could be a paraphyletic group, as the genera Amphiareus and Dysepicritus are not included in the tribe; (ii) the main subgroups, Oriini and Anthocorini, are monophyletic within Anthocoridae; (iii) three tribes of Blaptostethini, Xylocorini, and Scolopini are separated from the main anthocorid clade which is composed of Anthocorini, Cardiastethini, and Oriini, suggesting that Anthocoridae could not be monophyletic. We compared our molecular phylogeny to previous hypotheses of evolutionary relationships within Cimicoidea based on different anthocorid classification systems using alternative hypothesis tests (Kishino-Hasegawa and Shimodaira-Hasegawa tests). BayesTraits were used to examine the ancestral character states inferring historical habitat patterns of the Anthocoridae. Reconstruction of the ancestral habitat patterns of the Anthocoridae suggests that dead plants may have served as an important habitat for the common ancestor of anthocorids. The biological events such as diversification of angiosperms and anthocorid prey might have provided anthocorids with more habitat options, such as living plants; thereafter, Anthocorini and Amphiareus appeared to have evolved increasingly specialized habitat relationships.     

A molecular phylogeny for digger wasps in the tribe Ammophilini (Hymenoptera,Apoidea, Sphecidae)

The evolution of parental care strategies in aculeate (stinging) wasps and bees has been much studied from a functional perspective, but relatively little phylogenetic information is available to place this in a rigorous historical context, especially at the species level. We used mitochondrial cytochrome oxidase I and two nuclear genes, the elongation factor‐1α and LW rhodopsin, to investigate the phylogeny of Sphecidae digger wasps. We focus particularly on the tribe Ammophilini, a clade of nonsocial apoid wasps that exhibit unusually diverse parental care strategies. We analysed a 2232 bp dataset for 40 ammophilines plus nine other taxa from within the remaining Sphecidae. Our Bayesian phylogeny provides strong support for the monophyly of Ammophilini and for the monophyly of all six individual ammophiline genera, except that the position of P. affinis within the genus Podalonia is only weakly supported. The monophyly of some, but not all, previously designated species groups within the genus Ammophila is supported. We discuss the implications of our results for the evolution of morphological traits used previously in ammophiline systematics.     

A novel primer set for multilocus phylogenetic inference in East African cichlid fishes

The cichlid fishes in the East African Great Lakes are a prime model system for the study of adaptive radiation. Therefore, the availability of an elaborate phylogenetic framework is an important prerequisite. Previous phylogenetic hypotheses on East African cichlids are mainly based on mitochondrial and/or fragment‐based markers, and, to date, no taxon‐rich phylogeny exists that is based on multilocus DNA sequence data. Here, we present the design of an extensive new primer set (24 nuclear makers) for East African cichlids that will be used for multilocus phylogenetic analyses in the future. The primers are designed to work for both Sanger sequencing and next‐generation sequencing with the 454 technology. As a proof of principle, we validate these primers in a phylogenetically representative set of 16 cichlid species from Lake Tanganyika and main river systems in the area and provide a basic evaluation of the markers with respect to marker length and diversity indices.     

Evolutionary transitions in parental care and live bearing in vertebrates

We provide the first review of phylogenetic transitions in parental care and live bearing for a wide variety of vertebrates. This includes new analyses of both numbers of transitions and transition probabilities. These reveal numerous transitions by shorebirds and anurans toward uniparental care by either sex. Whereas most or all of the shorebird transitions were from biparental care, nearly all of the anuran transitions have been from no care, reflecting the prevalence of each form of care in basal lineages in each group. Teleost (bony) fishes are similar to anurans in displaying numerous transitions toward uniparental contributions by each sex. Whereas cichlid fishes have often evolved from biparental care to female care, other teleosts have usually switched from no care to male care. Taxa that have evolved exclusive male care without courtship-role reversal are characterized by male territoriality and low costs of care per brood. Males may therefore benefit from care through female preference of parental ability in these species. Primates show a high frequency of transitions from female care to biparental care, reflecting the prevalence of female care in basal lineages. In the numerous taxa that display live bearing by females, including teleosts, elasmobranchs, squamate reptiles and invertebrates, we find that live bearing has always evolved from a lack of care. Although the transition counts and probabilities will undoubtedly be refined as phylogenetic information and methodologies improve, the overall biases in these taxa should help to place adaptive hypotheses for the evolution of care into a stronger setting for understanding directions of change.     

The evolution of parental care in insects: A test of current hypotheses

Which sex should care for offspring is a fundamental question in evolution. Invertebrates, and insects in particular, show some of the most diverse kinds of parental care of all animals, but to date there has been no broad comparative study of the evolution of parental care in this group. Here, we test existing hypotheses of insect parental care evolution using a literature‐compiled phylogeny of over 2000 species. To address substantial uncertainty in the insect phylogeny, we use a brute force approach based on multiple random resolutions of uncertain nodes. The main transitions were between no care (the probable ancestral state) and female care. Male care evolved exclusively from no care, supporting models where mating opportunity costs for caring males are reduced—for example, by caring for multiple broods—but rejecting the “enhanced fecundity” hypothesis that male care is favored because it allows females to avoid care costs. Biparental care largely arose by males joining caring females, and was more labile in Holometabola than in Hemimetabola. Insect care evolution most closely resembled amphibian care in general trajectory. Integrating these findings with the wealth of life history and ecological data in insects will allow testing of a rich vein of existing hypotheses.     

Phylogeny of the cricket subfamily Eneopterinae (Orthoptera, Grylloidea, Eneopteridae) based on four molecular loci and morphology

The phylogenetic relationships of 39 species of Eneopterinae crickets are reconstructed using four molecular markers (16S rRNA, 12S rRNA, cytochrome b, 18S rRNA) and a large morphological data set. Phylogenetic analysis via direct optimisation of DNA sequence data using parsimony as optimality criterion is done for six combinations of weighting parameter sets in a sensitivity analysis. The results are discussed in a twofold purpose: first, in term of significance of the molecular markers for phylogeny reconstruction in Ensifera, as our study represents the first molecular phylogeny performed for this insect suborder at this level of diversity; second, in term of corroboration of a previous phylogeny of Eneopterinae, built on morphological data alone. The four molecular markers all convey phylogenetic signal, although variously distributed on the tree. The monophyly of the subfamily, that of three over five tribes, and of 10 over 13 genera, are recovered. Finally, previous hypotheses on the evolution of acoustic devices and signals in the Eneopterinae clade are briefly tested, and supported, by our new data set.     

Phylogeny and biogeography of the freshwater crab genus Johora (Crustacea: Brachyura: Potamidae) from the Malay Peninsula, and the origins of its insular fauna

The phylogeny and biogeography of the Malayan freshwater crab genus Johora was studied using two mitochondrial genes, 16S rRNA (560 bp) and cytochrome oxidase subunit I (COI) (616 bp), and one nuclear gene, histone 3 (H3) (328 bp). Johora is shown to be monophyletic and composed of three clades that correspond with the topography of the Malay Peninsula. The three clades were estimated to be of similar age ( c . 11 million years ago (mya)). The Malayan island of Pulau Tioman (with five species) was determined to have been colonised independently by two separate clades (at c . 11 and 5 mya, respectively), one of which evolved semiterrestrial habits, possibly in response to competition by the second. A partitioned Bremer support (PBS) analysis reveals that most of the support for the phylogenetic tree comes from the COI gene fragment and that the nuclear protein-encoding genes H3 is useful for reconstructing the relationships of Johora .     

Monophyly and interrelationships of Snook and Barramundi (Centropomidae sensu Greenwood) and five new markers for fish phylogenetics

Centropomidae as defined by Greenwood (1976) is composed of three genera: Centropomus, Lates, and Psammoperca. But composition and monophyly of this family have been challenged in subsequent morphological studies. In some classifications, Ambassis, Siniperca and Glaucosoma were added to the Centropomidae. In other studies, Lates+Psammoperca were excluded, restricting the family to Centropomus. Recent analyses of DNA sequences did not solve the controversy, mainly due to limited taxonomic or character sampling. The present study is based on DNA sequence data from thirteen genes (one mitochondrial and twelve nuclear markers) for 57 taxa, representative of all relevant species. Five of the nuclear markers are new for fish phylogenetic studies. The monophyly of Centropomidae sensu Greenwood was supported by both maximum likelihood and Bayesian analyses of a concatenated data set (12,888 bp aligned). No support was found for previous morphological hypotheses suggesting that ambassids are closely allied to the Centropomidae. Putative affinities between centropomids and Glaucosoma, Niphon, or Siniperca were strongly rejected by topology tests. In agreement with previous molecular hypotheses, our results place Centropomidae within a group of fishes that includes carangoids (e.g., jacks, remoras, dolphinfish, roosterfish, and cobia), flatfishes, barracudas, archerfishes, billfishes, moonfish, and threadfins. The phylogeny for the extant Centropomidae is ((Lates, Psammoperca), Centropomus).     

Phylogenetic analysis of the insect order Odonata using 28S and 16S rDNA sequences: a comparison between data sets with different evolutionary rates

Molecular phylogenetic analyses were conducted for the insect order Odonata with a focus on testing the effectiveness of a slowly evolving gene to resolve deep branching and also to examine: (i) the monophyly of damselflies (the suborder Zygoptera); and (ii) the phylogenetic position of the relict dragonfly Epiophlebia superstes. Two independent molecular sources were used to reconstruct phylogeny: the 16S rRNA gene on the mitochondrial genome and the 28S rRNA gene on the nuclear genome. A comparison of the sequences showed that the obtained 28S rDNA sequences have evolved at a much slower rate than the 16S rDNA, and that the former is better than the latter for resolving deep branching in the Odonata. Both molecular sources indicated that the Zygoptera are paraphyletic, and when a reasonable weighting for among‐site rate variation was enforced for the 16S rDNA data set, E. superstes was placed between the two remaining major suborders, namely, Zygoptera and Anisoptera (dragonflies). Character reconstruction analysis suggests that multiple hits at the rapidly evolving sites in the 16S rDNA degenerated the phylogenetic signals of the data set.     

Re-examination and phylogeny of the genus Chondrostoma based on mitochondrial and nuclear data and the definition of 5 new genera

Previous molecular phylogenetic studies of the genus Chondrostoma (Cyprinidae: Leuciscinae) were unable to resolve the relationship among its major species groups. In this paper we present a phylogeny for this genus, based on five mitochondrial genes and the nuclear gene beta-actin, comprising a total of 4068 bp. Bayesian inference using all gene fragments yielded a fully resolved phylogeny, compatible with topologies obtained from individual fragments using maximum parsimony and minimum evolution. Mapping of morphological characters critical to the rasping feeding mode of most Chondrostoma species indicates that they evolved several times, and questions the use of these characters in the traditional definition of the genus. Our findings led us to the definition of the following new genera: Achondrostoma, Iberochondrostoma, Pseudochondrostoma, Protochondrostoma and Parachondrostoma. Our data contradict the hypothesis of a rapid radiation during Lago Mare phase, suggested by previous studies.     

Phylogenetic analysis of the South American electric fishes (order Gymnotiformes) and the evolution of their electrogenic system: a synthesis based on morphology, electrophysiology, and mitochondrial sequence data

The order Gymnotiformes (South American electric fishes) is a fascinating assemblage of freshwater fishes that share the unusual ability to produce and sense electric fields used for electrolocation and social communication. In the last few decades, the electrogenic and electrosensory systems (EES) of these fish have served as an excellent model to study motor and sensory physiology in vertebrates. In an attempt to the evolution of characters associated with the EES in the group, we applied maximum-parsimony (MP), minimum-evolution (ME), and maximum-likelihood (ML) methods to analyze 302 aligned bases of the mitochondrial 12S rRNA and 416 bases of the mitochondrial 16S rRNA of 19 gymnotiform genera representing all six recognized families. Six catfish genera (order Siluriformes) were also sequenced and used as outgroups. The phylogenetic hypothesis resultant from molecular data analysis differs in some respects from previous hypotheses based on morphological studies. Our results were most informative within the family level, as we were unable to elucidate the relationships among deeper branches in this order with sufficient confidence by using molecular data alone. The phylogenetic information of both mitochondrial DNA segments appears to be affected by functional constraints, and the resultant topologies were sensitive to different weighting schemes and the algorithm used. Nonetheless, we found unanimous support for the following phylogenetic relationships: (1) the family Sternopygidae is an unnatural group, and Sternopygus is the sole representative of a unique lineage within the order; (2) the family Hypopomidae is not monophyletic; and (3) the order Gymnotiformes is composed of at least six natural clades: Sternopygus, family Apteronotidae, a new clade consisting of the remaining sternopygids, families Hypopomidae + Rhamphicthyidae, family Electrophoridae, and family Gymnotidae. By combining molecular, morphological, and physiological information, we propose a new hypothesis for the phylogeny of this group and suggest a new family Eigenmanniidae n. (order Gymnotiformes).      

Basal actinopterygian relationships: a mitogenomic perspective on the phylogeny of the "ancient fish"

The basal actinopterygians comprise four major lineages (polypteriforms, acipenseriforms, lepisosteids, and Amia) and have been collectively called "ancient fish." We investigated the phylogeny of this group of fishes in relation to teleosts using mitochondrial genomic (mitogenomic) data, and compared this to the various alternative phylogenetic hypotheses that have been proposed previously. In addition to the previously determined complete mitochondrial DNA (mtDNA) sequences from 14 teleosts and two outgroups, we used newly determined mitogenomic sequences of 12 purposefully chosen species representing all the ancient fish lineages plus related teleosts. This data set comprised concatenated nucleotide sequences from 12 protein-coding genes (excluding the ND6 gene and third codon positions) and 22 transfer RNA (tRNA) genes (stem regions only) and these data were subjected to maximum parsimony, maximum likelihood, and Bayesian analyses. The resultant trees from the three methods were well resolved and largely congruent, with most internal branches being supported by high statistical values. Mitogenomic data strongly supported not only the monophyly of the teleosts (osteoglossomorphs and above), but also a sister-group relationship between the teleosts and a clade comprising the acipenseriforms, lepisosteids, and Amia, with the polypteriforms occupying the most basal position in the actinopterygian phylogeny. Although the tree topology differed from any of the previously proposed hypotheses based on morphology, it exhibited congruence with a recently proposed novel hypothesis based on nuclear markers.     

中国沙塘鳢属鱼类线粒体12S rRNA基因序列分析

沙塘鳢属鱼类为东亚特有的小型淡水经济鱼类,中国产沙塘鳢属鱼类分类问题长期存在争议。本文测定了中国产沙塘鳢属鱼类全部种类的线粒体12S rRNA基因部分序列,结合GenBank中下载的2种日本沙塘鳢属鱼类和塘鳢科鱼类同源序列,探讨中国产4种沙塘鳢属鱼类的物种有效性,分析沙塘鳢属鱼类的系统发育关系。作者所使用的同源序列长度为690bp,其中变异位点258个,简约信息位点201个,包括插入/缺失位点34个,转换/颠换平均值为3.0,表明12S rRNA基因是研究沙塘鳢属鱼类系统发育关系的合适分子标记。基于p-distance模型的6种沙塘鳢属鱼类种内遗传距离为0.000—0.024,种间遗传距离为0.058—0.064,支持暗色沙塘鳢和中华沙塘鳢为不同种,中国产沙塘鳢属鱼类包括中华沙塘鳢、河川沙塘鳢、海丰沙塘鳢、鸭绿江沙塘鳢4个种的观点;至于中国还有没有新的沙塘鳢属鱼类,尚有待进一步研究。系统发育分析表明海丰海塘鳢是河川沙塘鳢的姐妹群,暗色沙塘鳢与O.hikimius的亲缘关系最为密切,而同属其余类群之间的系统发育关系则由于自展数据支持率较低而尚不明确。中国产沙塘鳢和日本产沙塘鳢并未单独分群,推测沙塘鳢属鱼类的共同原始祖先可能广泛分布于中国、朝鲜和日本等东亚地区,约在4.9—6.5百万年前的上新世开始分化,系统发育过程比较适合离散假说。     

Phylogenetic relationships of north American field crickets inferred from mitochondrial DNA data

A well-supported molecular phylogeny for North American Gryllus species based on a combined data set of mitochondrial (mt) DNA is presented. A total of 26 individuals representing 13 populations of 11 species of the genus Gryllus and 4 individuals of two outgroup species, Teleogryllus oceanicus and Acheta domestica, were sampled in this study. The complete cytochrome b gene (1036 bp) and a 500-bp fragment of the 16S rRNA gene were sequenced for each individual. Since results from separate analyses of the cytochrome b and 16S data sets, as well as a previously published mtDNA restriction-site data set, were not conflicting, all data were combined for phylogenetic analyses. The clade of European Gryllus was clearly separated from the North American clade. The amount of sequence divergence between these clades was significantly greater than within the clades, suggesting a basal drift-vicariant event in the genus. This is the first phylogenetic analysis of North American Gryllus that includes western species. Four well-supported groups were identified but their relationships showed no clear east-west structure. Our phylogeny supports the recent reassignment of G. integer Scudder 1901 from Texas to G. texensis Cade and Otte 2000. The evolution of cricket song and life cycle is discussed using the new phylogenetic framework.