Isolation by distance, linguistic similarity, and the genetic structure on Bougainville Island

Previous research has revealed extensive genetic variation among villages on Bougainville, in the Solomon Islands. Using previously published gene frequency data for seven loci, the role of isolation by distance in structuring genetic variation on Bougainville was reanalyzed. Newer methods of kinship estimation show that earlier estimates of the isolation by distance parameters were low. The fit of the model is highly significant (R2 = 0.409; P less than 0.001), and the parameter estimates indicate high isolation: a = 0.0538, b = 0.1978, L = -0.0057. Several methods of residual analysis were applied in order to determine factors affecting the fit of the model. Linguistic similarity has a significant effect on genetic variation once the effects of geographic distance are taken into account. Population-specific deviations from the expected model may be explained, in part, in terms of population history. Compared to other human populations, Bougainville Island shows an even greater among-group variation than has been suggested previously.     

Berberine contents and alkaloid profile of Berberis species from different altitudes

Roots, stem and leaves of eight species of Berberis collected from different altitudes in Garhwal, Himilaya, were analysed for berberine. Lowland species and types were found to have considerably higher berberine contents in all plant parts than sub-alpine and alpine species. In all, 12 or more alkaloids were separable in these species. Based on the similarity coefficient of leaf alkaloids, B. nepalensis was found to be identical to B. asiatica and B. vulgaris was identical to B. lycium. It is suggested that the concentration of berberine is probably a result of adaptive response to altitudinal gradient in addition to it being a genetic character of different species of Berberis.     

Global patterns of plant diversity

Summary Using 94 data sets from across the globe, we explored patterns of mean community species richness, landscape species richness, mean similarity among communities and mosaic diversity. Climate affected community species richness primarily through productivity while other climatic factors were secondary. Climatic equability affected species richness only in temperate regions where richness was greatest at high levels of temperature variability and low levels of precipitation variability. Landscape species richness correlated positively with community species richness. A global gradient in mean similarity existed but was uncorrelated with community species richness. Mean similarity was least and mosaic diversity was greatest between 25 and 30° latitude. The most diverse landscapes (low mean similarity) correlated with warm temperatures, high elevations, large areas and large seasonal temperature fluctuations. The most complex landscapes (high mosaic diversity) correlated with large areas, high productivity and warm winters. We compared diversity measures among continents and found only one significant difference: Australian landscapes have greater mosaic diversity than African landscapes. Based on our analyses we propose two hypotheses: (1) for plants, biotic interactions are more important in structuring landscapes in warmer climates and (2) longer isolated landscapes have more clearly differentiated ecological subunits.     

The notion of homology in current comparative biology

Current notions on homology, and its recognition, causation, and explanation are reviewed in this report. The focus is primarily on concepts because the formulation of precise definitions of homology has contributed little to our understanding of the issue. Different aspects or concepts of homology have been contrasted, currently the most important ones being the distinction between systematic and biological concepts. The systematic concept of homology focuses on common ancestry and on taxa; the biological concept tries to explain patterns of conservatism in evolution by shared developmental constraints. Similarity or correspondence is generally accepted as a primary criterion in the delimitation of homologues, albeit that this criterion is not without practical and theoretical problems. Apart from similarity, the biological concept of homology also stresses developmental individuality of putative homologous structures. Structural and positional aspects of homology can be separated, with positional homology acquiring an independent status. Similarity, topographic relationships, and ontogenetic development cannot be tests of homology. Within the cladistic paradigm, the most decisive test of homology is that of congruence; proponents of the biological-homology concept have been less concerned with test implications. Adopting a hierarchical view of nature suggests that characters have to be homologized at their appropriate level of organization. A taxic or systematic approach to homology has precedence over a transformational or biological approach. Nevertheless, pattern analysis and process explanations are not independent of each other.     

Similarity and local co-existence of species in regional biotas

The notion of community-wide character displacement hypothesizes that locally co-existing sets of competing species should be less similar than expected when compared to random expectations from a broader regional species pool. Here I use a mechanistic approach to the niche concept to show how this expectation is dependent on the types of traits involved. I investigate how two different niche components, those that relate to species' requirements (or responses to environmental factors) versus those that relate to species' impacts (or effects on environmental factors), affect predictions about the similarity of locally co-existing species. In contrast with more conventional approaches that focus on species impacts, I focus on species responses to conclude that locally co-existing species should be more similar in such traits than expected on the basis of random assortment from a larger equilibrium regional biota. In addition, I explore the evolutionary implications of exceptions that might favour the co-existence of species with dissimilar traits (especially those that determine species' impacts on the environment) and conclude that these implications differ when species compete for shared resources, interact via shared predators, or interact via both mechanisms. The analysis developed in this paper shows that the co-existence of species that are more similar than expected by chance is not incompatible with the notion of strongly interacting species in saturated local communities near equilibrium.     

Association between relationship measures based on AFLP markers, pedigree data and morphological traits in barley

 Thirty one barley lines were used to investigate the agreement between three relationship measures: genetic similarities based on 681 AFLP-markers, coefficients of co-ancestry based on pedigree data, and generalised distance based on 25 morpological characters (morphological distance). Bootstrap analysis was used to estimate the accuracy of the correlation estimates. AFLP-based genetic similarities showed a poor-to-moderate correlation with the coefficients of co-ancestry within the core set of 25 European two-row spring barleys. Morphological distance was not significantly correlated with either genetic similarity or the coefficient of co-ancestry. The precision of all correlation-coefficient estimates, however, was low. The inclusion of two European winter barleys, two North American two-row spring barleys, and two North American six-row spring barleys in the AFLP-analysis resulted in a much stronger correlation between genetic similarity and the coefficient of co-ancestry. This suggests good opportunities for the use of AFLP-markers to assess genetic diversity by distinguishing between the major ecotypes of barley. Additionally, each of the eight primer combinations used in the AFLP-analysis was able to identify all 31 lines uniquely, showing the usefulness of AFLPs for cultivar identification. Because of the inaccuracy of the investigated relationship measures, resulting in low values of the correlation-coefficient estimates, prediction of the breeding behaviour of parent combinations may be improved by the use of a combination of relationship measures, thus decreasing the effect of their individual independent errors. Received: 24 February 1997 / Accepted: 23 June 1997     

Distribution of sequences related to the Bg transposable element of maize in Zea and related genera

Thirty-four accessions from Zea and 10 accessions from related genera were assayed for the presence of Bg, a transposable element originally found in maize (Zea mays ssp. mays). Bg-like sequences, identified as hybridizing bands on Southern blots, were visualized in all Zea accessions and were present in approximately equal numbers in teosinte and maize. With the exception of Tripsacum dactyloides, all accessions from related genera failed to hybridize with the Bg probes, even at reduced stringency. A comparison of the restriction patterns of related inbred lines revealed numerous common hybridizing fragments. An index of molecular similarity (MS) was used to determine the degree of similarity between pairs of inbred lines. Computed MS values endorse an inbred relationship and are in good agreement with published results of cluster analysis on these inbred lines.     

群落食物网间的相似性测度

群落是指一定地段或生境里各种生物种群构成的结构单元。群落内各物种不是孤立存在的,它们之间存在着极为复杂的营养联系。一种植物常有多种害虫取食,一种害虫可取食多种植物,同时又被多种天敌捕食或寄