Evolution of gastropod mitochondrial genome arrangements

<p>Abstract</p> <p>Background</p> <p>Gastropod mitochondrial genomes exhibit an unusually great variety of gene orders compared to other metazoan mitochondrial genome such as e.g those of vertebrates. Hence, gastropod mitochondrial genomes constitute a good model system to study patterns, rates, and mechanisms of mitochondrial genome rearrangement. However, this kind of evolutionary comparative analysis requires a robust phylogenetic framework of the group under study, which has been elusive so far for gastropods in spite of the efforts carried out during the last two decades. Here, we report the complete nucleotide sequence of five mitochondrial genomes of gastropods (<it>Pyramidella dolabrata</it>, <it>Ascobulla fragilis</it>, <it>Siphonaria pectinata</it>, <it>Onchidella celtica</it>, and <it>Myosotella myosotis</it>), and we analyze them together with another ten complete mitochondrial genomes of gastropods currently available in molecular databases in order to reconstruct the phylogenetic relationships among the main lineages of gastropods.</p> <p>Results</p> <p>Comparative analyses with other mollusk mitochondrial genomes allowed us to describe molecular features and general trends in the evolution of mitochondrial genome organization in gastropods. Phylogenetic reconstruction with commonly used methods of phylogenetic inference (ME, MP, ML, BI) arrived at a single topology, which was used to reconstruct the evolution of mitochondrial gene rearrangements in the group.</p> <p>Conclusion</p> <p>Four main lineages were identified within gastropods: Caenogastropoda, Vetigastropoda, Patellogastropoda, and Heterobranchia. Caenogastropoda and Vetigastropoda are sister taxa, as well as, Patellogastropoda and Heterobranchia. This result rejects the validity of the derived clade Apogastropoda (Caenogastropoda + Heterobranchia). The position of Patellogastropoda remains unclear likely due to long-branch attraction biases. Within Heterobranchia, the most heterogeneous group of gastropods, neither Euthyneura (because of the inclusion of <it>P. dolabrata</it>) nor Pulmonata (polyphyletic) nor Opisthobranchia (because of the inclusion <it>S. pectinata</it>) were recovered as monophyletic groups. The gene order of the Vetigastropoda might represent the ancestral mitochondrial gene order for Gastropoda and we propose that at least three major rearrangements have taken place in the evolution of gastropods: one in the ancestor of Caenogastropoda, another in the ancestor of Patellogastropoda, and one more in the ancestor of Heterobranchia.</p

The chromosomal constitution of spermatozoa from eight normal, healthy brazilian men

Apresenta-se a análise citogenética de cromossomos de espermatozóides de oito homens brasileiros normais, utilizando-se a técnica de fertilização heteróloga homemhamster. Os resultados obtidos são semelhantes aos descritos em outros laboratórios que dominam esta técnica. Obteve-se freqüência de 5.4% (variação de 1.0-13.5%) de aberrações cromossômicas, sendo 1.4% de aberrações estruturais (variação de 0.0-3.3%), freqüência de hiper-haploidia de 2.0% (variação entre 0.0-5.1%) e freqüência de hipo-haploidia de 5.6% (variação de 0.0-11.3%). A diferença entre as proporções de espermatozóides X (54.1%) e Y (45.9%) foi significativa, ao nível de 5%.We describe the chromosomal analyses of sperm from eight normal brazilian men using the human sperm-hamster egg fusion technique. The frequency of total chromosomal aberrations was 5.4% (range, 1.0-13.5%), of structural aberrations 1.4% (range, 0.0-3.3%), of hyperhaploidy 2.0% (range, 0.0-5.1%) and of hipohaploidy 5.6% (range,0.0-11.3%). The proportion of X-bearing (54.1%) and Y-bearing (45.9%) spermatozoa differed significantly at 5% level. The results obtained in this work are similar to those reported in the literature

Gradients of genetic diversity and differentiation across the distribution range of a Mediterranean coral: Patterns, processes and conservation implications

Aim: How historical and contemporary eco-evolutionary processes shape the patterns of genetic diversity and þÿdifferentiation across species distribution range remain Focusing on the orange stony coral, Astroides calycularis, we (a) characterized the pattern of neutral genetic diversity across the distribution range; (b) gave insights into the underlying processes; and (c) discussed conservation implications with emphasis on a national park located on a hotspot of genetic diversity. Location: South Mediterranean Sea and Zembra National Park. Methods: We combined new data from 12 microsatellites in 13 populations located in the Centre and in the Western Periphery of the distribution range with a published dataset including 16 populations from the Western and Eastern Peripheries. We analysed the relationship among parameters of genetic diversity (He, Ar(g)) and structure (population-specific FST) and two measures of geographic peripherality. We compared two estimators of pairwise genetic structure (GST, DEST) across the distribution range. The evolutionary and demographic history of the populations following the Last Glacial Maximum was reconstructed using approximate Bayesian computations and maximum-likelihood analyses. We inferred the contemporary connectivity among populations from Zembra National Park and with the neighbouring area of Cap Bon. Results: We demonstrate a decrease in genetic diversity and an increase in genetic differentiation from the Centre to the Eastern and Western Peripheries of the distribution range. Populations from Zembra show the highest genetic diversity reported in the species. We identified a spillover effect towards Cap Bon. Main conclusions: The patterns of genetic diversity and þÿdifferentiation are most likely explained by the postglacial range expansion hypothesis rather than the þÿ central peripheral hypothesis. Enforcement of conservatio

The synaptic process in Locusta migratoria spermatocytes by synaptonemal complex anal

We describe the synaptic process during meiotic prophase in spermatocytes from Locusta migratoria, using synaptonemal complex (SC) spreads analyzed by light (LM) and electron (EM) microscopy. At leptotene, a stage of short duration, unpaired axial elements begin to be assembled. Synapsis starts at zygotene, beginning usually at the terminal regions of the bivalents, either at the proximal, centromeric end or at the distal, non-centromeric end; interstitial initiation of synapsis was only occasionally observed in the longer chromosomes. Pairing is asynchronous, and shorter chromosomes are the first to complete synapsis. At pachytene all bivalents are fully synapsed. Diplotene is characterized by the progressive fragmentation of SCs; fragmentation is asynchronous, and affects mainly the longer chromosomes, while the shorter ones maintain their morphology up to late diplotene

Gastropod mitogenomics: no support for a pulmonate clade

Comunicación presentada en la 72nd Annual American Malacological Society y en la 39th Annual Western Malcological Society, celebrada en Seattle del 29 de julio al 3 de agosto de 2006.In an effort to improve our knowledge of the phylogeny of gastropods, we have sequenced anew the complete mitochondrial genomes of five species of gastropods including one representative of Opisthobranchia (Ascobulla fragilis), one of Heterostropha (Pyramidella dolabrata), and three representatives of Pulmonata (Siphonaria pectinata, Onchidella celtica, and Myosotella myosotis). The new sequences have been aligned with all available complete mitochondrial genomes of gastropods from GenBank and subjected to different phylogenetic analyses. We discuss the phylogeny of gastropods, with special emphasis on the lack of support for the monophyly of Pulmonata and the evolution of mitochondrial gene order arrangement.Peer reviewe

Molecular Phylogeny of Euthyneura (Mollasca: Gastropoda)

A new phylogenetic hypothesis for Euthyneura is proposed based on the analysis of primary sequence data (mitochondrial cox1, trnV, rrnL, trnL(cun), trnA, trnP, nad6, and nad5 genes) and the phylogenetic utility of two rare genomic changes (the relative position of the mitochondrial trnP gene, and an insertion/deletion event in a conserved region of the mitochondrial Cox1 protein) is addressed., Both sources of phylogenetic information clearly rejected the monophyly of pulmonates, a group of gastropods well supported so far by morphological evidence. The marine basommatophoran pulmonate Siphonaria was placed within opisthobranchs and shared with them the insertion of a Glycine in the Cox 1 protein. The marine systellommatophoran pulmonate Onchidella was recovered at the base of the opisthobranch + Siphonaria clade. Opisthobranchs, Siphonaria, and Onchidella shared the relative position of the mitochondrial trnP gene between the mitochondrial trnA and nad6 genes. The land snails and slugs (stylommatophoran pulmonates) were recovered as an early split in the phylogeny of advanced gastropods. The monophyly of the Euthyneura (Opisthobranchia + Pulmonata) was rejected by the inclusion of the heterostrophan Pyramidella.C.G. was sponsored by a predoctoral fellowship of the Ministerio de Ciencia y Tecnología. This work received financial support from projects of the Ministerio de Ciencia y Tecnología to J.T. (REN2000-0890/GLO), to J.L.C. (REN2001-1956-C17-02/GLO), and to R.Z. (REN2001-1514/GLO).Peer Reviewe

The complete mitochondrial genome of the nudibranch Roboastra europaea (Mollusca: Gastropoda) supports the monophyly of opisthobranchs

The complete nucleotide sequence (14,472 bp) of the mitochondrial genome of the nudibranch Roboastra europaea (Gastropoda: Opisthobranchia) was determined. This highly compact mitochondrial genome is nearly identical in gene organization to that found in opisthobranchs and pulmonates (Euthyneura) but not to that in prosobranchs (a paraphyletic group including the most basal lineages of gastropods). The newly determined mitochondrial genome differs only in the relative position of the trnC gene when compared with the mitochondrial genome of Pupa strigosa, the only opisthobranch mitochondrial genome sequenced so far. Pupa and Roboastra represent the most basal and derived lineages of opisthobranchs, respectively, and their mitochondrial genomes are more similar in sequence when compared with those of pulmonates. All phylogenetic analyses (maximum parsimony, minimum evolution, maximum likelihood, and Bayesian) based on the deduced amino acid sequences of all mitochondrial protein-coding genes supported the monophyly of opisthobranchs. These results are in agreement with the classical view that recognizes Opisthobranchia as a natural group and contradict recent phylogenetic studies of the group based on shorter sequence data sets. The monophyly of opisthobranchs was further confirmed when a fragment of 2,500 nucleotides including the mitochondrial cox, rrnL, nad6, and nad5 genes was analyzed in several species representing five different orders of opisthobranchs with all common methods of phylogenetic inference. Within opisthobranchs, the polyphyly of cephalaspideans and the monophyly of nudibranchs were recovered. The evolution of mitochondrial tRNA rearrangements was analyzed using the cox1+rrnL+nad6+nad5 gene phylogeny. The relative position of the trnP gene between the trnA and nad6 genes was found to be a synapomorphy of opisthobranchs that supports their monophyly.C.G. was sponsored by a predoctoral fellowship of the Ministerio de Ciencia y Tecnología. This work received financial support from projects of the Ministerio de Ciencia y Tecnología to J.T. (REN2000-0890/GLO) and to R.Z. (REN2001-1514/GLO).Peer Reviewe

Hypothesized mitochondrial gene rearrangements during Gastropoda evolution based on observed gene orders and the recovered BI phylogenetic hypothesis

Inversion (indicated by the arrow) and transpositions of protein coding, tRNAs and rRNA genes are depicted among the different taxa (except between -and - Heterobranchia due to the high number of changes). Genes encoded by the minor strand are underlined. Genes located in apomorphic arrangements are colored.<p><b>Copyright information:</b></p><p>Taken from "Evolution of gastropod mitochondrial genome arrangements"</p><p>http://www.biomedcentral.com/1471-2148/8/61</p><p>BMC Evolutionary Biology 2008;8():61-61.</p><p>Published online 26 Feb 2008</p><p>PMCID:PMC2291457.</p><p></p