Mark Dowton

Mitochondrial gene rearrangements as phylogenetic characters in the invertebrates: the examination of genome 'morphology'

Mitochondrial gene rearrangements are the latest tool in the arsenal of phylogeneticists for investigating historical relationships. They are complex molecular characters that may provide more reliable evidence of ancestry than comparative molecular data. Here we review the phylogenetic utility of mitochondrial gene rearrangements, and find that despite isolated incidences of convergence, derived gene order appears highly congruent with phylogenies produced from other sources of data. We calculate that the chance of two mitochondrial genomes sharing the same derived genome organisation is only 1/2664, but caution that this ignores the possibility that the (as yet uncharacterised) gene rearrangement mechanism may greatly increase the chance of convergence. Broader taxonomic surveys of mitochondrial genome organisation will lead to a more realistic indication of the historical incidence of convergence in genome organisation.

INCREASED GENETIC DIVERSITY IN MITOCHONDRIAL GENES IS CORRELATED WITH THE EVOLUTION OF PARASITISM IN THE HYMENOPTERA

A higher AT content and rate of mtDNA sequence divergence was found in parasitic wasps (Apocrita) compared with nonparasitic wasps (Symphyta). The compositional bias was reflected in extreme codon bias for a cytochrome oxidase I protein coding gene fragment as well as in the types of amino acid substitutions that have occurred during the evolution of this gene fragment. In some instances, compositional bias influenced the definition of a conservative amino acid change. The increased rate of mtDNA sequence evolution probably arose during the early Jurassic, coincident with the first appearance of parasitic wasps in the fossil record. Our results suggest a causal link between the rate of sequence divergence and the parasitic lifestyle.

Mitochondrial genome organization and phylogeny of two vespid wasps

We sequenced the entire mitochondrial genome of Abispa ephippium (Hymenoptera: Vespoidea: Vespidae: Eumeninae) and most of the mitochondrial genome of Polistes humilis synoecus (Hymenoptera: Vespoidea: Vespidae: Polistinae). The arrangement of genes differed between the two genomes and also differed slightly from that inferred to be ancestral for the Hymenoptera. The genome organization for both vespids is different from that of all other mitochondrial genomes previously reported. A number of tRNA gene rearrangements were identified that represent potential synapomorphies for a subset of the Vespidae. Analysis of all available hymenopteran mitochondrial genome sequences recovered an uncontroversial phylogeny, one consistent with analyses of other types of data.

EVIDENCE FOR AT-TRANSVERSION BIAS IN WASP (HYMENOPTERA : SYMPHYTA) MITOCHONDRIAL GENES AND ITS IMPLICATIONS FOR THE ORIGIN OF PARASITISM

Abstract. We inferred the incidence of nucleotide conversions in the COI and 16S rRNA mitochondrial genes of members of the Symphyta and basal Apocrita (Hymenoptera). Character-state reconstructions in both genes suggested that conversions between A and T (AT transversions) occurred much more frequently than any other type of change, although we cannot wholly discount an underlying transition bias. Parsimony analysis of COI nucleotide characters did not recover phylogeny; e.g., neither the Tenthredinoidea nor Apocrita were recovered as monophyletic. However, analysis of COI amino acid characters did recover these relationships, as well as others based on fossil and morphological evidence. Analysis of 16S rRNA characters also recovered these relationships providing conversions between A and T were down-weighted. Analysis of the combined data sets gave relatively strong support for various relationships, suggesting that both data sets supported similar topographies. These data sets, both separately and combined, suggested that the phytophagous Siricidae were more closely related to the predominantly parasitic Apocrita than were the ectoparasitic Orussoidea. This suggests that the wasp parasitic lifestyle did not have a single origin, unless the Siricidae have more recently reverted to phytophagy. Alternatively, parasitism evolved twice independently, once in the Orussoidea and again in the Apocrita. The latter scenario is supported by the observation that the evolution of parasitism was accompanied by a tendency for the larvae to develop inside plant tissues. Adaptations that accompanied the movement of wasps into a confined, wood-boring habitat may have preadapted them to becoming ectoparasitic.n

Somatostatin-14 and somatostatin-28 levels are light-driven and vary during development in the chicken retina

The relative levels of somatostatin-14 and somatostatin-28 were determined during both perinatal development and variations in lighting conditions in the chicken retina. During perinatal development of the retina, somatostatin-14 predominated in recently hatched chickens, whereas somatostatin-28 predominated in the retinas of older chickens. In mature chickens, the levels of both somatostatin-14 and somatostatin-28 increased during the light and decreased during the dark. Our results suggest that these two forms of somatostatin are released proportionally and in parallel.

Purification of glutamine synthetase by adenosine-affinity chromatography

Abstract The ability to purify insect flight muscle glutamine synthetase using various adenosine ligands was assessed. The enzyme bound most strongly to the ADP analogue (5′-ADP-agarose), followed by the NADPH analogue (2′,5′-ADP-Sepharose 4B), and least strongly to the cyclic AMP analogue (3′,5′-ADP-agarose). In all cases, binding was strongest in the presence of Mn2+ when compared to Mg2+. These results suggest that the binding of glutamine synthetase to adenosine-affinity media is related to the participation of Mn·ADP in the γ-glutamyl transferase reaction that is catalysed by glutamine synthetase.