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Parthenogenetic Organisms (parthenogenetic + organism)
Selected AbstractsTemporal dynamics of genotypic diversity reveal strong clonal selection in the aphid Myzus persicaeJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2006C. VORBURGER Abstract Parthenogenetic organisms often harbour substantial genotypic diversity. This diversity may be the result of recurrent formations of new clones, or it may be maintained by environmental heterogeneity acting on ecological differences among clones. In aphids, both processes may be important because obligate and cyclical parthenogens can form mixed populations. Using microsatellites, I analysed the temporal dynamics of clonal diversity in such a population of the aphid Myzus persicae over a 1-year period. The frequency distribution of clonal genotypes was very skewed, with many rare and few common clones. The relative frequencies of common clones underwent strong and rapid changes indicative of intense clonal selection. Differences in their host associations suggest that these shifts may partly be caused by changes in the abundance of annual host plants. Other selective factors of potential importance are also discussed. New, sexually produced genotypes made a minor contribution to clonal diversity, consistent with the observed heterozygote excess characteristic of predominantly asexual populations in M. persicae. [source] Evidence for predominant clones in a cyclically parthenogenetic organism provided by combined demographic and genetic analysesMOLECULAR ECOLOGY, Issue 12 2000L. Haack Abstract Aphids are particularly interesting models in the study of genetic and demographic components of plant adaptation because of their breeding system which combines parthenogenesis and sexual reproduction (i.e. cyclical parthenogenesis), and the frequent emergence of host-adapted races reported in this group. In this paper, patterns of host adaptation were assessed on local populations of the aphid Sitobion avenae by following their demographic and genetic structure in a maize field for two consecutive years. The existence of putative generalist (polyphagous) or specialized (host-adapted) genotypes was also investigated by comparing the genotypic distribution of this aphid on maize and other cultivated host plants, using five microsatellite loci. Although population dynamics revealed strong variation in aphid abundance during the colonization period on maize, two genotypes identified at seven additional microsatellite loci were predominant and exhibited stable frequencies over cropping season and between years. Based on present and earlier studies, these two prevalent genotypes were shown to survive on different host plants other than maize, to colonize large geographical zones and to persist parthenogenetically for several years. All these data strongly suggest that these two genotypes are asexual generalist clones that could have been favoured by agricultural practices encountered in western Europe. Besides these two clones, a continual replacement of rare genotypes was observed on maize in both years. Hypotheses involving selection via aphid,plant interactions and natural enemies were proposed for explaining the disappearance of these genotypes on maize. [source] Isolation and characterization of microsatellite loci in the aphid species, Rhopalosiphum padiMOLECULAR ECOLOGY RESOURCES, Issue 1-2 2001Jean-Christophe Simon Abstract Due to their properties for resolving patterns of population genetic structure, microsatellites are increasingly used in studies of breeding systems. Here, eight polymorphic microsatellite loci were isolated and characterized in the aphid Rhopalosiphum padi, in which populations show a mixture of cyclically and obligatory parthenogenetic lines. These loci were then applied to distinguish between 55 parthenogenetic lines of R. padi collected across France. Interestingly, they allowed to detect several copies of the same genotypes among the sample, confirming the great sensitivity of microsatellites and their usefulness in population genetic studies of parthenogenetic organisms. [source] Temporal patterns of geographic parthenogenesis in a freshwater snailBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2007FRIDA BEN-AMI Geographic parthenogenesis describes the observation that parthenogenetic organisms tend to occupy environments different from those of their close, sexually reproducing relatives. These environments are often described as extreme or disturbed habitats. We examined whether patterns of geographical parthenogenesis persist over time, by conducting a 3-year life-history survey and comparing two very proximate habitats of the freshwater snail Melanoides tuberculata: Nahal Arugot, a desert stream naturally disturbed by flash floods, and Or Ilan, a stable freshwater pond. Both sites occur in a xeric environment and are subject to otherwise similar biotic (e.g. parasites, predators) and climatic conditions. In the stable habitat, male frequencies and snail densities were significantly higher than in the disturbed one, whereas infection levels, mean embryo counts, and water temperatures were similar at both sites. Additionally, male frequencies declined after density decreased, thereby providing evidence for geographical parthenogenesis via reproductive assurance. Infection prevalence was very low regardless of reproduction mode. Although further genetic work is required, the apparent metapopulation structure of M. tuberculata in the Judean desert may be suitable for evaluating other possible explanations of geographical parthenogenesis. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 711,718. [source] | ||||||||||