Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.      

Proton transport through membranes induced by weak acids: A study of two substituted benzimidazoles

Summary We report here a kinetic study of the mechanism by which the weak acid TTFB (4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole) transports protons across phospholipid bilayer membranes. A previous kinetic study of the homologous dichloro compound, DTFB, revealed that the rate limiting step for proton translocation was the back diffusion of the neutral, HA, form of the weak acid; we conclude here that this is also the rate limiting step for proton translocation with TTFB. At high concentrations of either DTFB or TTFB the charged permeant species is an HA ₂ ^– complex. The kinetic analysis and independent measurements reveal that the permeability of the membrane to HA and adsorption coefficients of A^– and HA are an order of magnitude higher for TTFB than for DTFB. When either DTFB or TTFB was present in a solution where the pH was less than the pK of the weak acid, an unusual relaxation in the current was noted on application of a voltage step. The amplitude of the relaxation decreased as the voltage was increased. This relaxation is possibly due to a reorientation of the benzimidazole molecules at the membrane-solution interface. We also report experiments performed with DTFB on mitochondria. It was possible to reconcile these results with the bilayer data and, therefore, with the chemiosmotic hypothesis by postulating that the dielectric constant of the mitochondrial membrane is greater than that of a bilayer formed with decane as a solvent. To demonstrate the effect of dielectric constant on permeability, we replaced decane by 1-chlorodecane. This increased the capacitance of the artificial bilayer by a factor of two and the permeability of the bilayer to the A^– form of DTFB by two orders of magnitude.