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  • Author: H.-R. Gregorius x
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Abstract

Studies on plant communities of various annual species suggest that there are particular biotic interactions among individuals from different species which could be the basis for long-term species coexistence. In the course of a large survey on species-genetic diversity relationships in several forest tree communities, it was found that statistically significant differences exist among isozyme genotype frequencies of conspecific tree groups, which differ only by species identity of their neighbours. Based on a specific measure, the association of the neighbouring species with the genotypes of the target species or that of the genotypes with the neighbouring species was quantified. Since only AAT and HEK of the five analysed enzyme systems differed in their genotype frequencies among several tree groups of the same target species, a potential involvement of their enzymatic function in the observed differences was discussed. The results of this study demonstrate a fine-scale genetic differentiation within single tree species of forest communities, which may be the result of biotic interactions between the genetic structure of a species and the species composition of its community. This observation also suggests the importance of intraspecific genetic variation for interspecific adaptation.

Abstract

The conclusions drawn from studies of genetic differentiation among populations largely determine our understanding of ecological and population genetic processes. These conclusions basically depend on the applied type of genetic marker and the method of measuring and estimating genetic differentation. However, concerns have been raised about the conceptual appropriateness of common methods of measuring genetic differentiation. The present paper contributes to the clarification of the problems involved by recalling the conceptual characteristics of FST (= GST), by specifying basic tests of the major causal factors of genetic differentiation with the help of permutation analysis, by comparing FST and Hedrick’s new normalization F’ST with the basic index δ of differentiation for data on allozymes and microsatellites obtained from 6 oak stands. All three descriptors display small values, among which δ is largest and closely followed by F’ST, while FST is distinctly smaller than both across all loci. Degrees of covariation of δ with FST and F’ST differ distinctly between allozymes and microsatellites as a probable consequence of confounding aspects of differentiation with aspects of fixation in the FST descriptors. Permutation analysis reveals that the boundary conditions provided by the number of populations and their (sample) sizes as well as the overall genetic variation across population samples determine the order of magnitude of differentiation. This mathematical artefact undermines the widely held opinion that small degrees of differentiation at many loci are the result of extensive gene flow or recent joint history. Differentation patterns vary considerably among allozyme loci (indicating the action of homogenizing and diversifying selection). In contrast, microsatellite loci consistently display significant differentiation as can be explained by mechanisms of non-recurrent mutation. These observations apply to all three descriptors for the relatively high within population polymorphism observed in the studied stands. At least for low within population polymorphism close to fixation, however, it is shown theoretically that the predictions may diverge distinctly among the three descriptors.

Abstract

The biological units that are the object of management, preservation and improvement for the development of sustainable productive systems in natural areas, need to be differentiated and analyzed. Attending to this need, a new morphological distance is presented in this work. This distance is based on qualitative criteria and is applied to numerical taxonomy studies. The characteristics of this trait allow its comparison with the genetic distance of GREGORIUS (1974). Both parameters are essential tools in basic studies of native species populations. The morphological distance is applied to reveal genetically differentiated units in a swarm of hybrids between closely related species, and this result is compared with the results obtained from the application of traditional methods of numerical taxonomy.

Abstract

Relationships between species diversity and genetic diversity, the two most important elements of biodiversity, have recently attracted considerable interest in the field of community genetics. The present study contributes to this issue by addressing three questions that seem to have been ignored so far, namely whether the use of (a) different diversity measures, of (b) different components of diversity, and of (c) different genetic traits may lead to different assessements of speciesgenetic diversity relationships. For this purpose, data on species composition and genetic traits were collected from the natural regeneration of nine forest communities, which consist of three pure and six mixed tree stands located in the Thuringian forest area. The genetic traits comprised one DNA (AFLP) and five isozyme traits all of which were determined in all species. In contrast to other studies, the species diversity was determined for two components, SD (species diversity) and NeS (effective number of genetically distinct species), and the genetic diversity was determined for three components, TSGD (the transspecific genetic diversity taken over all species of a community), ISGD and NGS (each describing a special average of intraspecific genetic diversity). Each component was quantified by measures of diversity representing four orders of the Renyi/Hillfamily. The orders correspond to the degree to which prevalence of types is considered in the diversity measure (at the lowest order, known as richness, prevalence is disregarded, with increasing order, the diversity measure reports prevalent types only). In our data, the diversity measured for each genetic trait separately showed a great range of variation across traits and components of diversity even in the same stand. The choice of the diversity component thus turned out to have a substantial effect on the assessment of the level of genetic diversity within stands. This prompted more detailed studies of the relationships between species and genetic diversity. Relationships were quantified with the help of the coefficient of co-variation, and the statistical significance of the co-variations was verified through permutation tests. The co-variations between SD and TSGD were found to be generally positive and in most cases significant, but the co-variation declined with increasing orders of diversity for most of the genetic traits. In contrast, the co-variation between SD and ISGD was not consistent for the four orders of diversity. In particular, the co-variations for the highest order were found to be negative for all traits. The results of our explorative study thus demonstrate that the assessment of levels of genetic diversity within stands as well as species-genetic interrelations critically depend on the choice of the diversity component, of the order of diversity, and of the genetic trait. These observations lend support to different and even opposing hypotheses on the processes potentially generating species-genetic relationships. Therefore, strategies in the conservation of biodiversity, for example, are suggested to be related more specifically to the components and orders of diversity to be safegarded and to consider the functions of genetic traits in relation to adaptationally relevant environmental factors.