Hans-Rolf Gregorius

Is autochthony an operational concept

In spite of the high approval and the reference in many forest law and forestry service regulations, the idea of autochthony still seems to lack the definiteness and operationality that at least enables unambiguous specification of its ecological and evolutionary significance. This makes the assessment of autochthony questionable. Explication of the expectations connected with the idea reveals that, when applied to populations, it primarily addresses their adaptedness to the environmental conditions of a special site in combination with the adaptability that can be preserved at this site. Necessary prerequisites for realizing high degrees of adaptedness and adaptability are provided by regular environmental conditions together with balanced gene inflow from genetically heterogeneous and differentiated neighboring conspecific populations. Since successful adaptational processes reduce adaptational stress levels, adaptedness increases the capacity to support the genetic loads that are required for preserving adaptability to temporary as well as to lasting changes. Herewith, adaptability to temporary and lasting changes depends primarily on resident and immigrant genetic information, respectively. The latter requires metapopulation structures with balanced gene flow systems. Because of the complexity of this situation, a comprehensive assessment of autochthony is impossible. However, much of this complexity can be avoided by concentrating on the historical, geographical and genealogical characteristics of populations as separate units of adaptation. It is argued and illustrated by an example, that such an approach to the assessment of autochthony can be realized with the help of phylogeographic methods by testing the hypothesis of positive correspondence between phylogenetic relatedness and spatial distance.

Measuring Association Between Two Traits

A measure of association is introduced that is based on a conceptual rather than a model approach in order to ensure its broad applicability. The basis of the concept involves two variables or traits α and β of members of a population. The association of the β-state with the α-state is measured by the degree to which members of given α-state share their β-state. This formulation yields an index of association, which is applicable to all categories of traits, including discontinuous and continuous traits as well as combinations of these. Complete association of one trait with the other is equivalent to the existence of a functional relationship of the second to the first trait. Therefore, the degree of association can be understood as the closeness of the relations between two variables to a non-specified functional relationship. This feature in connection with the asymmetry of the index attests its suitability for cause-effect analyses. In fact, the conceptual approach to the measurement of association yields a conclusive method of detection and description of functional relationships between variables together with a method for quantification of the strictness of these relationships. The legitimacy of the correlation coefficient and of disequilibrium indices as measures of association is briefly addressed.

Genetische Grundlagen der Ökosystemstabilität

ZusammenfassungUm die wünschenswerte Allgemeinheit der Darstellung gewährleisten zu können, wird eine auf systemtheoretischen Auffassungen beruhende Erläuterung der wichtigsten Zusammenhänge gewählt. Auf dieser Grundlage stellt sich Ökosystemstabilität als Angepaßtheit und Anpassungsfähigkeit eines offenen dynamischen Systems an seine Umweltbedingungen dar. Als Ziel jedes Anpassungsprozesses kann die Erhaltung der Identität des Ökosystems gelten, die sich in den durch die charakteristischen externen Bedingungen geprägten Kennzeichen seines Stoff-, Energie- und Informationshaushaltes zeigt. Dem Informationshaushalt obliegt die Aufgabe der Steuerung von Stoff- und Energieflüssen (-Umwandlungen). Da die Information ihre materielle Basis in der Erbsubstanz DNS hat und die Organisation dieser Information durch die genetischen Systeme der Populationen als Einheiten der Anpassung und Evolution geregelt ist, sind hier die genetischen Grundlagen der Ökosystemstabilität angesiedelt. Nach ihrer Einordnung in interspezifische Mechanismen werden die elementaren intraspezifischen Anpassungsmechanismen von Populationen unter Berücksichtigung ihrer physiologischen und (mikro-)evolutionären Komponenten skizziert. Abschließend werden einige der wichtigsten populationsgenetischen Methoden und Parameter zur Analyse von Anpassungsprozessen und -potentialen zusammengestellt und kurz erläutert.Die vorliegende Ausarbeitung hat zum Ziel, die Position der Genetik im Rahmen ökosystemarer Stabilitätsbedingungen zu verdeutlichen. Hierdurch soll einem vielfach vorgetragenen Wunsch nachgekommen werden. Um die fachübergreifende Verständigung zu erleichtern, wird die ohnehin im Grunde systemtheoretische Auffassung, welche den ökologischen Vorstellungen der Stabilität zugrundeliegt, die Erläuterungen beherrschen. Auch wenn eine weitgehend durch die Forschung an Waldökosystemen inspirierte Auffassung immer wieder durchscheinen sollte, ist doch die Darstellung allgemeinerer Zusammenhänge beabsichtigt. So wird das für die Evolution biologischer Systeme zentrale und in der forstlichen Literatur zwar geläufige, aber selten explizit so benannte Konzept der Anpassung benutzt werden, um mit Bezug auf die Prinzipien der Stabilisierung eine konsistente Beziehung zwischen der Ebene des Ökosystems und der genetisch relevanten Ebene der Population herzustellen. Der gewählte systemtheoretische Zugang mag noch wenig vertraut sein, er ist jedoch von der Sache her zwingend und greift aktuelle, nicht zuletzt durch die Waldschadensforschung angestoßene Entwicklungen auf (siehe z. B. das IMA-Querschnittseminar “Wirkungskomplex Stickstoff und Wald” des Umweltbundesamtes 1995).SummaryThe most important relationships are explained based on a systems theory approach to make sure that the general validity of the representation is maintained. In this context ecosystem stability can be understood in terms of a adaptedness and adaptability of an open dynamical system to its environmental conditions. The objective of every adaptational process is the maintenance of ecosystem identity, manifest in the typical features of its material, energy and information balance as affected by characteristic external conditions. The information balance controls material and energy flows (and conversions). Since the genetic code DNA is the material basis underlying information and since its organization is regulated by the genetic systems of populations as units of adaptation and evolution, this is the context in which the genetic elements of ecosystem stability are to be considered. After classification according to inter-specific mechanisms the fundamental intra-specific adaptational mechanisms of populations are outlined, with consideration of physiological and (micro-) evolutionary components. Finally some of the most important population genetic methods and parameters for the analysis of adaptational processes and potentials are compiled and discussed.

Reinforcement of genetic coherence: a single-locus model.

Genetic coherence and genetic separation are the outcome of evolutionary mechanisms which maintain genetic variation within populations through recombination on the one hand, and which divide this variation via speciation between reproductively (recombinatorically) more or less isolated populations on the other. While mechanisms of speciation have received considerable attention in biology, their counterpart, mechanisms of genetic coherence, are addressed only implicitly, if at all. Usually, genetic coherence is intuitively associated with the forces maintaining genetic polymorphisms and thus potential for flexible adaptational reaction of populations. However, so far no models seem to exist which explain the evolution of genetic coherence as the natural counterpart of genetic separation or speciation. In this paper a single-locus model is analyzed, in which a mutant allele is introduced into a resident stable diallelic polymorphism, and where this allele is equivalent to one of the resident alleles in all respects with the exception of mating relations. The conditions for replacement of the resident allele by its selectively equivalent mutant are obtained with reference to the associated mating relations. It turned out that for heterozygote advantage the mutant replaces the selectively equivalent resident allele if it increases the mating preferences for carriers of other alleles. The evolution of lower such preferences requires heterozygote inferiority, which confirms the Wallace effect of speciation (by reinforcement). It is argued that this observation suggests that non-selective constituents of the mating system form the section of the genetic system that is responsible for moderating the genetic load implied by adapting selection while simultaneously securing the adaptational potential embodied in the resident allelic variation. Mating systems thus serve the preservation of adaptability.

Sustainable treatment of resources: The genetic basis

Any treatment of a resource is considered sustainable, if it diminishes neither this resource nor any other irreversibly. A conceptually consistent and practicable presentation of the principles of sustainable treatment of resources is given using a system-oriented approach. In this approach the resource appears as a system that is characterized by the capacity to deal to a certain degree with exogenous impacts without losing its identity and integrity. Realization of this capacity rests on the existence of mechanisms of self-regulated regeneration with their characteristic feedback relations. For a treatment of a resource to be sustainable, it is thus necessary to guard the intactness of the resource’s own mechanisms of self-regeneration as well as those of all affected systems. Many anthropogenic forms of resource treatment violate even this basic prerequisite of sustainability by disconnecting essential feedback loops. Populations are the most elementary biological resources capable of indefinite self-regeneration, and certain specified mechanisms of the genetic system realize this capacity. Special emphasis is put on the two-fold function of the environment as modifying these mechanisms and providing the conditions for their operation. On this basis it is argued that any treatment of a population can be sustainable only if it obeys the following three prerequisites: (i) intactness (operability) of the mechanisms of the genetic system, (ii)realization of the mechanisms’ external conditions for operation (operational conditions), and (iii)availability of genetic variation for alteration of these mechanisms. Indication of these prerequisites is argued to be most effective when the system analytical approach is applied. In essence, this approach consists in modeling the potentially affected mechanisms and their operational conditions, such that they fulfill prerequisites (i), (ii) and (iii). Incompatibility between the model predictions and observations then leads to rejection of the hypothesis of sustainable treatment. The advantage of this approach to indication over an approach involving mere comparative interpretation of genetic processes and indices of genetic variation is demonstrated.

Reinforcement of genetic coherence in a two-locus model

BackgroundIn order to maintain populations as units of reproduction and thus enable anagenetic evolution, genetic factors must exist which prevent continuing reproductive separation or enhance reproductive contact. This evolutionary principle is called genetic coherence and it marks the often ignored counterpart of cladistic evolution. Possibilities of the evolution of genetic coherence are studied with the help of a two-locus model with two alleles at each locus. The locus at which viability selection takes place is also the one that controls the fusion of gametes. The second locus acts on the first by modifying the control of the fusion probabilities. It thus acts as a mating modifier whereas the first locus plays the role of the object of selection and mating. Genetic coherence is enhanced by modifications which confer higher probabilities of fusion to heterotypic gametic combinations (resulting in heterozygous zygotes) at the object locus.ResultsIt is shown that mutants at the mating modifier locus, which increase heterotypic fusions but do not lower the homotpyic fusions relative to the resident allele at the object locus, generally replace the resident allele. Since heterozygote advantage at the object locus is a necessary condition for this result to hold true, reinforcement of genetic coherence can be claimed for this case. If the homotypic fusions are lowered, complex situations may arise which may favor or disfavor the mutant depending on initial frequencies and recombination rates. To allow for a generalized analysis including alternative models of genetic coherence as well as the estimation of its degrees in real populations, an operational concept for the measurement of this degree is developed. The resulting index is applied to the interpretation of data from crossing experiments in Alnus species designed to detect incompatibility relations.