Genet age in marginal populations of two clonal Carex species in the Siberian Arctic

During a Swedish-Russian expedition to northern Siberia 1994, we sampled two marginal populations of two Carex species at two high arctic sites (C. stuns Drej. on Faddeyevsky Island and C. ensifolia V. Krecz ssp, arctisibirica Jurtz. at north-eastern Taymyr Peninsula), both north of previously documented localities in that areas for the two species. These populations were composed of a few distinct patches of ramet colonies, some of them shaped like fairy rings with dead centres. We measured the size of all colonies and collected samples for detailed morphometric analyses of rhizome growth. By using RAPD (random amplified polymorphic DNA) analysis we established that the largest colony at each site consisted of a single genet, based on 41 polymorphic bands amplified with three primers. Fouled samples from each of two additional colonies of C. stuns on Faddeyevsky Island were analysed and showed that clones of the same species at the same site were relatively dissimilar (Dice's similarity index 0.26-0.43). We then assumed that each ramet colony represented a single genet. Based on the morphometric data, we developed a deterministic growth model that simulates the clonal growth of these species and enabled estimates of the time since establishment of the genets. The estimated age of the five C. stans clones varied from 17 to 154 yr and the age of the two C. ensifolia ssp. arctisibirica clones was well over 3000 yr

Stop worrying; start growing: Risk research on GM crops is a dead parrot: it is time to start reaping the benefits of GM

Opponents of genetically modified crops continue to raise concerns about risk, despite 20 years of research disproving their claims. Science should close the book on risk research and turn to studying the economic and environmental benefits of agricultural biotechnolog

A general model for selection among modules in haplo-diploid life histories

Genetic variation resulting from changes during somatic development in modular organisms may be inherited by subsequent generations due to the late development of their germ line. As a consequence, both sexually and asexually produced offspring may be genetically variable. The presence of heritable intraclonal variation and the great life history variation among modular organisms requires that evolutionary theory does not limit selection to only that occurring among individuals resulting from meiosis and zygote formation. To allow for variation within clonal lineages, and encompass a wide variety of life histories, we construct a simple model of selection among modules in life histories that contain both haploid slid diploid phases, such as that seen among many multicellular algae. Selection among modules is a demographic process with module performance depending on its genotype at a single locus with two alleles. The model is used to simulate the spread of a beneficial allele in life histories that vary in the relative amount of sexual and asexual reproduction. The time taken for allele fixation is shown to depend on both demographic and genetic factors

Avoiding the counterfactuals: Research design in assesing the impact of agricultural research

Two things strike the eye in the literature and debate on the impact of agricultural research. Firstly, it is not unsurprisingly dominated by economists using cost-benefit analysis. Secondly and more surprisingly, much space is devoted to the discussion of counterfactuals, i.e. by an argument of the type: “If this research had not been made, yield development (or whatever indicator) would have been less than it currently is.” Counterfactuals are shunned by historians but crop up in the literature on impact assessment for a simple reason, viz. that assessment is made ex post and without careful benchmarking having been done ex ante. This paper argues that historians are right, that counterfactual arguments in principle are dubious, at least in social impact assessment and that alternative research designs, more useful for causal attribution should be aimed for. In the first section follows a review of previous CGIAR work in impact assessment and a general methodological discussion. This is followed by a review of the methodologies, first for social impact assessment followed by an examination of environmental indicators. In the concluding section we propose a selection of case studies in which it would be possible to apply the methods and indicators suggested

Luminescence control in the marine bacterium Vibrio fischeri: An analysis of the dynamics of lux regulation

A mathematical model has been developed based on the fundamental properties of the control system formed by the lux genes and their products in Vibrio fischeri. The model Clearly demonstrates how the components of this system work together to create two, stable metabolic states corresponding to the expression of the luminescent and non-luminescent phenotypes. It is demonstrated how the cell can "switch" between these steady states due to changes in parameters describing metabolic processes and the extracellular concentration of the signal molecule N-3-oxohexanoyl-L-homoserine lactone. Ln addition, it is shown how these parameters influence how sensitive the switch mechanism is to cellular LuxR and N-3-oxohexanoyl-L-homoserine lactone and complex concentration. While these properties could lead to the collective phenomenon known as quorum sensing, the model also predicts that under certain metabolic circumstances, basal expression of the lux genes could cause a cell to luminesce in the absence of extracellular signal molecule. Finally, the model developed in this study provides a basis for analysing the impact of other levels of control upon lux regulation. (C) 2000 Academic Press

Genetic variation and clonal diversity in four clonal sedges (Carex) along the Arctic coast of Eurasia

We studied the structure of genetic variation (at both ramet- and genet-level) and clonal diversity within and among populations in the four closely related arctic clonal sedges Carex bigelowii, C. ensifolia, C. lugens and C. starts by use of allozyme markers. Compared to other sedges and arctic plants, the studied taxa all had high levels of genetic variation, both within populations and taxa. These taxa contained most of the total gene diversity (H-T) within populations and a small part of the diversity among populations (G(ST) ranged 0.05-0.43). Carex bigelowii had genetic variation (H-S = 0.173, mean for populations) at a comparable level to other outbreeding arctic plants and to other widespread, rhizomatous and mainly outbreeding Carex species. In contrast, C. ensifolia (H-S = 0.335), C. lugens (H-S = 0.339) and C. stans (H-S = 0.294) had within-population variations that were higher than in most other studied Carex species and for arctic plants in general. Genetic variation was not related to any tested environmental variable, but it was lower in areas deglaciated only 10 000 years BP compared to areas deglaciated 60 000 years BP or not glaciated at all during the Weichselian. All the populations were multiclonal, except for two populations of C. starts that were monoclonal. In contrast to genetic variation, clonal diversity decreased with latitude and did not differ between areas with different times of deglaciation. In accordance with previous studies, C. bigelowii and C. lugens were found to be outbreeding, while C. ensifolia and C. stans had mixed mating systems