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.      

Phase response versus positive and negative division delay in animal cells

The time of median cell division in V79 Chinese hamster cells following high serum pulses was determined for two synchronous cell generations following mitotic selection. Differences in cell cycle time for each pair of pulse and control cultures were computed and plotted as a function of time of serum pulse. This phase response curve for hamster cells with an 8.5 h cell cycle shows a characteristic biphasic pattern. Beginning 0.5 h after mitotic selection, pulses with serum produce delays in the midpoint of the subsequent mitotic waves. Delay is maximum at 1.5 h. Delays give way abruptly to advances at 2.5 h and the amount of advance then decreases as pulses are given between 3 and 5 h into the cycle. At 5 h decreasing advances become delays, with increasing delays due to serum pulses occurring between 5 and 6 h. Delays again give way abruptly to advances at 6 h and again the amount of advance decreases through the late portion of the cycle. Pulses very late in the cycle appear to generate phase delays. This biphasic response to serum is interpreted as an expression of an underlying time-keeping oscillator whose period is nominally of 4 h duration.