RESUMO
A molecular phylogeny is presented for the subfamily Littorininae (including representatives of all subgeneric taxa and all members of a group of southern-temperate species formerly classified as 'Nodilittorina'), based on sequence data from two nuclear (18S rRNA, 28S rRNA) and two mitochondrial (12S rRNA, CO1) genes. The phylogeny shows considerable disagreement with earlier hypotheses derived from morphological data. In particular, 'Nodilittorina' is polyphyletic and is here divided into four genera (Echinolittorina, Austrolittorina, Afrolittorina new genus, and the monotypic Nodilittorina s.s.). The phylogenetic relationships of 'Littorina' striata have been controversial and it is here transferred to the genus Tectarius, a surprising relationship for which there is little morphological support. The relationships of the enigmatic Mainwaringia remain poorly resolved, but it is not a basal member of the subfamily. The two living species of Mainwaringia are remarkable for a greatly elevated rate of evolution in all four genes examined; it is suggested that this may be connected with their protandrous hermaphroditism, which is unique in the family. The molecular phylogeny provides a new framework for the adaptive radiation of the Littorininae, showing more frequent shifts between habitats and climatic regimes than previously suspected, and striking parallelism of morphological characters. The fossil record of littorinids is poor, but ages of clades are estimated using a calibration based on a Lower Eocene age of the genus Littoraria. Using these estimates, the antitropical distribution of Littorina and Afrolittorina is an ancient pattern of possibly Cretaceous age. The five members of Austrolittorina show a Gondwanan distribution in Australia, New Zealand, and South America. Based on the morphological uniformity within this clade, relatively recent (Plio-Pleistocene) trans-Pacific dispersal events seemed a likely explanation, as proposed for numerous other congeneric marine taxa. However, molecular estimation of ages of divergence suggest an initial vicariance between Australian and South American lineages at 40-73Ma, contemporary with the later stages of fragmentation of the Gondwanan supercontinent, followed by more recent (but still mid-Cenozoic) dispersal events across the Tasman Sea and the Pacific Ocean. Afrolittorina is another Cretaceous clade, now restricted to southern Africa and southern Australia, but divergence between these lineages (29-55Ma) post-dates Gondwanan fragmentation. Within both Austrolittorina and Afrolittorina all sister-species divergences are estimated to fall in the range 10-47Ma, so that there is no evidence for speciation events in the Plio-Pleistocene.
Assuntos
Filogenia , Caramujos/classificação , Adaptação Biológica , África Austral , Animais , Austrália , Sequência de Bases , Primers do DNA/genética , Complexo IV da Cadeia de Transporte de Elétrons/genética , Evolução Molecular , Genes de RNAr/genética , Geografia , Dados de Sequência Molecular , Fenótipo , Caramujos/genética , América do SulRESUMO
Here we show that multiple DNA sequences, similar to the mitochondrial cytochrome oxidase I (COI) gene, occur within single individuals in at least 10 species of the snapping shrimp genus Alpheus. Cloning of amplified products revealed the presence of copies that differed in length and (more frequently) in base substitutions. Although multiple copies were amplified in individual shrimp from total genomic DNA (gDNA), only one sequence was amplified from cDNA. These results are best explained by the presence of nonfunctional duplications of a portion of the mtDNA, probably located in the nuclear genome, since transfer into the nuclear gene would render the COI gene nonfunctional due to differences in the nuclear and mitochondrial genetic codes. Analysis of codon variation suggests that there have been 21 independent transfer events in the 10 species examined. Within a single animal, differences between the sequences of these pseudogenes ranged from 0.2% to 20.6%, and those between the real mtDNA and pseudogene sequences ranged from 0.2% to 18.8% (uncorrected). The large number of integration events and the large range of divergences between pseudogenes and mtDNA sequences suggest that genetic material has been repeatedly transferred from the mtDNA to the nuclear genome of snapping shrimp. Unrecognized pseudogenes in phylogenetic or population studies may result in spurious results, although previous estimates of rates of molecular evolution based on Alpheus sister taxa separated by the Isthmus of Panama appear to remain valid. Especially worrisome for researchers are those pseudogenes that are not obviously recognizable as such. An effective solution may be to amplify transcribed copies of protein-coding mitochondrial genes from cDNA rather than using genomic DNA.
Assuntos
Decápodes/genética , Mitocôndrias/genética , Pseudogenes/genética , Animais , Núcleo Celular/genética , DNA/química , DNA/genética , DNA Mitocondrial/química , DNA Mitocondrial/genética , Decápodes/classificação , Complexo IV da Cadeia de Transporte de Elétrons/genética , Dosagem de Genes , Dados de Sequência Molecular , Mutação , Filogenia , Análise de Sequência de DNARESUMO
The effects of adding chloramphenicol before inoculation and during exponential growth of Streptomyces venezuelae (3022a) in fermentors were studied. The responses of the organism during synthesis of chloramphenicol (in a glycerol-serine-lactate medium) were compared with those in media supporting less (glycerol-nutrient broth-yeast extract) or no synthesis (glucosemineral salts). In systems where little or no synthesis of the chloramphenicol occurred, addition of the antibiotic induced micromorphological and ultrastructural abnormalities similar to those reported for sensitive bacteria. There was also an increase in the frequency of mesosomes and electron-light areas. It was suggested that the former may be associated with activity of chloramphenicol hydrolase and the latter with storage and/or excretion of the breakdown product; N-acetyl p-nitro-phenylserinol. When chloramphenicol synthesis occurred, addition of the antibiotic had less effect on the micromorphology or ultrastructure of S. venezuelae as permeability barriers to external chloramphenicol had been established. Electron-light areas were frequent, possibly being associated with storage and excretion of precursors of chloramphenicol.
Assuntos
Cloranfenicol/farmacologia , Streptomyces/efeitos dos fármacos , Membrana Celular/ultraestrutura , Parede Celular/ultraestrutura , Cloranfenicol/biossíntese , Meios de Cultura , Streptomyces/crescimento & desenvolvimento , Streptomyces/ultraestruturaRESUMO
Streptomyces venezuelae (3022a) was grown in flask cultures and fermentors, using three media having differential effects on chloramphenicol production. Micromorphology, ultrastructure and chloramphenicol concentrations were studied during the growth cycle in each medium. Chloramphenicol production was greatest in the glycerol-serine-lactate (GSL) medium, less in the glycerol-nutrient broth-yeast extract (GNY) medium and very low in glucose-mineral salts (GA) medium. In GSL and GA, much growth was in the form of microcolonies, especially in flask cultures, while short hyphal fragments predominated in GNY. The major ultrastructural features were the high frequency of mesosomes in fragmenting hyphae in GNY, and electron-transparent zones which appeared during chloramphenicol synthesis in GSL. None of the structural abnormalities induced by chloramphenicol in sensitive organisms were observed in S. venezuelae despite high levels of the antibiotic in GSL medium.