Ecology and biogeography of plant communities associated with the post Plio-Pleistocene relict Rhododendron ponticum subsp. baeticum in southern Spain

Aims Rhododendron ponticum L. is reputed to be a post Plio‐Pleistocene relict plant species with a disjunct distribution that comprises the Iberian Peninsula to the west and the Euxinian region plus some restricted Mediterranean areas to the east. We analysed the ecological range (of subsp. baeticum) in the western area (Aljibe Mountains, north of the Strait of Gibraltar) to understand the factors determining the present area limitation. Location Sierra del Aljibe, north of the Strait of Gibraltar (Iberian Peninsula). Methods We selected 20 riparian sites where R. ponticum is common, and compiled data on the ecological diversity of associated woody species and ferns. We established a 500‐m main transect in each site, along the stream or river course, in which we placed five 20‐m‐long plots at regular intervals. We recorded physiographic habitat features, woody plants and fern abundance, and the number of R. ponticum individuals. Results Rhododendron ponticum in southern Spain is restricted to riparian forests in acidic soils (pH 4.0–6.4), and is mainly found on the banks of inclined and enclosed streams. In our inventory we recorded 59 woody taxa and 12 ferns, with R. ponticum being the dominant species of the understorey (mean abundance 78.6%). The communities are characterized by a high incidence of the humid warm temperate element, both in number of species (18.8 ± 3.7 per site) and abundance; meanwhile, the presence of the modern Mediterranean element (mean number of species 3.4 ± 3.8 per site) appears to be favoured by disturbance. These ecological–historical groups of taxa also show distinct patterns of typological habit, frequency of endemism, infrageneric diversity and geographical range. Populations of R. ponticum are characterized by a very variable density of seedlings in many sites, and the virtual lack of juveniles. Main conclusions Riparian forests of the Aljibe Mountains constitute a refuge for R. ponticum where the species persists, but populations appear to be in decline. The narrow ecological range of R. ponticum in the area strongly contrasts with its wide amplitude in the eastern natural area, mainly the Euxinian region, where R. ponticum probably finds better conditions due to the environmental heterogeneity of the region, and the lack of a hot dry season.     

Instrumental test to estimate a model of forecast yield: a non-parametric application to the pollen index in South Italy

A statistical test is described to verify the characteristics of the biological information contained in the dynamics of the flowering process. The test focuses on interactions between the pollen index and climatic variables to investigate if the biological indicator can synthesise the information of the pre-flowering phases. The multiple-regression model is built upon two pre-flowering climate macro-indicators extracted by Principal Component Analysis (PCA) and the optimised pollen index is obtained by non-parametric estimation. The empirical analysis is applied to 15 stations located in southern Italy in regions that have a longstanding tradition of olive production. Using the variance explained, we find that an optimised pollen index is fairly well predicted by the pre-flowering climatic data. We conclude that the optimised pollen index makes more parsimonious the modelling for predicting olive production.     

Genetic diversity within and among 11 juvenile populations of green alder (Alnus crispa) in Canada

Germinated seeds from 11 populations of green alder [ Alnus crispa (Ait.) Pursh] sampled in four Canadian provinces were analysed for electrophoretically demonstrable diversity of 10 enzymes encoded by 15 structural loci. Of these, nine were polymorphic, and on average, 52% of the loci per population were polymorphic. Assuming a diploid model of expression, average level of expected heterozygosity was 0.11 with nearly all populations in Hardy-Weinberg equilibrium for the set of polymorphic loci analysed. No significant inbreeding and associated subpopulation structuring were noted. Rates of gene flow appeared high within and among populations. Although little divergence was observed among populations, genetic and geographical distances between populations were related. Discriminant and cluster analyses revealed a pattern of genetic variation associated with geography. Populations from northern Quebec were poorly differentiated, whereas western populations from Alberta exhibited a larger degree of genetic differentiation. Introgresive hybridization with the sympatric species Alnus sinuata (Regel) Rydberg and partial isolation in the West are suggested as an explanation for this larger differentiation. The occurrence and significance of rare alleles is discussed in relation to the importance of geographical distance in the process of population differentiation in this species.     

Gene assignment by means of somatic cell hybrids: a new method for the analysis of data

Summary A statistical approach to the interpretation of data from gene assignment with somatic cell hybrids is presented. The observed data are analysed under a variety of hypotheses. The fit to the hypotheses is compared by means of the likelihood obtained under a given hypothesis. Two of these hypotheses are related to fundamental questions: is a gene responsible for the enzyme observation and if so, is that gene located on a specific chromosome or could it change its position and be sometimes on chromosome j and, in another hybrid line, on chromosome k? The other hypotheses concern the assignment of the gene to just one of the chromosomes.To improve the traditional data analysis approach we considered additional information: the uncertainties and possible errors of laboratory methods in all our calculations and the length of the donor chromosomes in connection with one specific hypothesis.This method allows us to account for the reliability of the investigation methods and the nature of the hybrid lines involved. Data can be evaluated at different error probabilities within a realistic range in order to compare and discuss results.     

Cluster analysis as a method for evaluation of genetic similarity in specific host — parasite interaction (Lactuca sativa — Bremia lactucae)

Summary In gene-for-gene systems, specificity of hostparasite interactions is most often estimated qualitatively using the symbols +, –, (i.e. susceptibility and/or resistance). In large sets (interaction patterns) it becomes impossible to analyze numerous data by mere comparison. This is overcome by application of cluster analysis. In our experiments the methods in question were used to estimate the data obtained in a study on interactions between more than 220 Lactuca sativa cultivars and 12 Bremia lactucae physiological races (isolates) of Czechoslovak origin. The matrix of similarity coefficients was analyzed by hierarchical clustering. Similarity and/or dissimilarity of host R-genotypes was graphically expressed using the method of two principal components. The results obtained are related to genetic constitution of race specific resistance of the host and the possibility of predicting effective resistance sources.     

Position of the Peptide Linkage in Glutamyl-Taurine from Calf Brain Synaptic Vesicles

To elucidate the position of the peptide bond in glutamyl-taurine this dipeptide was extracted from calf brain synaptic vesicles and subjected to paper electrophoresis. It was analyzed further in an automatic amino acid analyzer prior and subsequent to acid hydrolysis. Both alpha- and gamma-forms were found to be present in approximately equal amounts.     

Estimation of uncertainties in X-ray refinement results by use of perturbed structures

The uncertainties in the refined parameters for a 1.5-A X-ray structure of carbon-monoxy (FeII) myoglobin are estimated by combining energy minimization with least-squares refinement against the X-ray data. The energy minimizations, done without reference to the X-ray data, provide perturbed structures which are used to restart conventional X-ray refinement. The resulting refined structures have the same, or better, R-factor and stereochemical parameters as the original X-ray structure, but deviate from it by 0.13 A rms for the backbone atoms and 0.31 A rms for the sidechain atoms. Atoms interacting with a disordered sidechain, Arg 45 CD3, are observed to have larger positional uncertainties. The uncertainty in the B-factors, within the isotropic harmonic motion approximation, is estimated to be 15%. The resulting X-ray structures are more consistent with the energy parameters used in simulations.     

Phylogenetic systematics of the nymphaeales

A cladistic analysis was applied to reveal the phylogenetic relationships among the Nymphaeales. Seventeen out of twenty three characters in gross morphology, anatomy and palynology were analyzed, for their evolutionary polarities. From the results of the present analysis, the phylogenetic status of each genus and their relationships were clarified: 1)Nelumbo is a distinct taxon and is presumed to have originated from an ancestral stock of the Nymphaeales; 2)Ceratophyllum has a close phylogenetic relationship withCabomba; and 3) in the Nymphaeaceaesensu stricto, Nuphar and the remaining genral constitute a monophyletic group. A conclusion obtained from the present analysis was that the following three families should be recognized in the Nymphaeales; Nelumbonaceae Nymphaeaceae, and Ceratophyllaceae. The generaBrasenia andCabomba are traditionally classified in the Nymphaeaceae or in the independent family Cabombaceae. However, they should be included in the family Ceratophyllaceae.