A study of pre- and postganglionic fibres in the intestinal nerve (Remak's nerve) of the chicken

Summary The mean peak CV's of two electrophysiologically defined groups of fibres in the intestinal nerve of the chicken have been determined.One group of fibres is constituted by the processes of enteric cholinergic neurones which project along the side branches of the intestinal nerve and synapse within the nerve trunk. These preganglionic fibres have a mean peak CV (at 40 °C) of 0.31 m·s^–1.The other group is made up of fibres of postganglionic neurones which project orally along the nerve trunk. The results suggest that some postganglionic neurones project only as far as the next ganglion whilst others project beyond the next two ganglia for distances greater than 5 mm. The postganglionic fibres have a mean peak CV (at 40 °C) of 0.71 m·s^–1.These figures demonstrate that both pre- and postganglionic fibres are unmyelinated. The temperature coefficient (Q₁₀) for the CV of unmyelinated fibres in the intestinal nerve was 1.57.Abbreviations CAP compound action potential - CV conduction velocity - Q ₁₀ temperature coefficient     

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.      

The use of simultaneous sampling bottle and vertical net collections to describe the dynamics of a zooplankton population

Simultaneous collections of zooplankton were made at four stations in the Plover Clove Reservoir using Friedinger sampling bottles and vertical Nakai plankton net hauls. Comparison of the results obtained revealed certain obvious numerical and spatial anomalies, and it is suggested that these result from inherent characteristics of the two types of apparatus together with behavioural responses and physical attributes of the individual zooplankton species. Statistical correlation between these two methods was generally good in terms of the seasonal patterns of distribution of the population, but in terms of depth distribution and the relative abundance of the individual species of the population few significant correlations resulted. It is therefore suggested that unless merely seasonal trends are required, it is advisable to use more than one sampling apparatus to obtain valid data concerning the overall dynamics of such a zooplankton population.Department of Botany, University of Hong Kong