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Intense Selection (intense + selection)
Selected AbstractsPrion-like Doppel gene polymorphisms and scrapie susceptibility in portuguese sheep breedsANIMAL GENETICS, Issue 3 2010P. Mesquita Summary The establishment of an association between prion protein gene (PRNP) polymorphisms and scrapie susceptibility in sheep has enabled the development of breeding programmes to increase scrapie resistance in the European Union. Intense selection for PRNP genotype may lead to correlated selection for genes linked to PRNP. We intended to investigate if any association exists between genetic variation in prion-like protein Doppel gene (PRND) and scrapie susceptibility, determined through PRNP genotyping. Sampling included 460 sheep from eight Portuguese breeds and the PRND gene coding region was analysed by multiple restriction fragment-single strand conformation polymorphism (MRF-SSCP), whereas PRNP genotyping was carried out by primer extension. A synonymous substitution (c.78G>A) was detected in codon 26 of the PRND gene, in all breeds except Churra Mondegueira. Linkage disequilibrium was found between the PRND and PRNP loci (P = 0.000). Specifically, PRND was monomorphic in the 45 animals with the more resistant ARR/ARR PRNP genotype (P = 0.003), whereas a higher frequency of PRND heterozygotes (GA) was associated with ARQ/AHQ (P = 0.029). These results constitute preliminary evidence of an association between a polymorphism in the PRND gene and scrapie susceptibility, and indicate that the possibility of undesirable consequences from widespread selection for PRNP genotype on genetic diversity and reproduction traits needs to be further investigated. [source] Adaptation, extinction and global changeEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 1 2008Graham Bell Abstract We discuss three interlinked issues: the natural pace of environmental change and adaptation, the likelihood that a population will adapt to a potentially lethal change, and adaptation to elevated CO2, the prime mover of global change. 1.,Environmental variability is governed by power laws showing that ln difference in conditions increases with ln elapsed time at a rate of 0.3,0.4. This leads to strong but fluctuating selection in many natural populations. 2.,The effect of repeated adverse change on mean fitness depends on its frequency rather than its severity. If the depression of mean fitness leads to population decline, however, severe stress may cause extinction. Evolutionary rescue from extinction requires abundant genetic variation or a high mutation supply rate, and thus a large population size. Although natural populations can sustain quite intense selection, they often fail to adapt to anthropogenic stresses such as pollution and acidification and instead become extinct. 3.,Experimental selection lines of algae show no specific adaptation to elevated CO2, but instead lose their carbon-concentrating mechanism through mutational degradation. This is likely to reduce the effectiveness of the oceanic carbon pump. Elevated CO2 is also likely to lead to changes in phytoplankton community composition, although it is not yet clear what these will be. We emphasize the importance of experimental evolution in understanding and predicting the biological response to global change. This will be one of the main tasks of evolutionary biologists in the coming decade. [source] Xylem root and shoot hydraulics is linked to life history type in chaparral seedlingsFUNCTIONAL ECOLOGY, Issue 1 2010Robert B. Pratt Summary 1.,Shrubs in fire prone chaparral communities have evolved different life history types in response to fire. A key to understanding the evolution of life history type differences is to understand how physiological traits are linked to differences in life history type. Vascular adaptations are important for delivering an efficient and stable water supply to evergreen chaparral shrub leaves. This study tested for a link between vascular physiology and life history type in chaparral shrubs. 2.,Chaparral shrub species along the south-western coast of North America survive wildfire by three different life histories. Non-sprouters are killed by fire and re-establish exclusively through germination of fire-stimulated seeds, facultative sprouters re-establish by a combination of vegetative sprouting and fire-stimulated seeds, and obligate sprouters re-establish exclusively by vegetative sprouting because their seeds do not survive fire. Non-sprouters and facultative sprouters establish seedlings in the open canopy post fire environment, whereas obligate sprouters establish seedlings in the shady understory of the mature chaparral canopy. 3.,Seedlings of nine species (Rhamnaceae) representing three each of the different life history types were grown in deep containers in a common garden under treatments of sun and shade. Hydraulic conductance was measured using a high-pressure flow meter for all organs, and a vacuum technique was used to measure conductance of fine and woody roots. We predicted that non-sprouters would exhibit greater hydraulic efficiency than the sprouting species, and that facultative sprouters would be more efficient than the shade tolerant obligate sprouters. 4.,Non-sprouters had the greatest hydraulic conductance per unit leaf and sapwood area at the whole seedling level, whereas facultative and obligate sprouters were not different. Comparing hydraulic conductance across major organs (from fine roots to leaves) showed that the hydraulic system was well coordinated. At the whole seedling level, the root system was more of a bottleneck than the shoot system. This pattern was consistent with high resistance extraxylary pathways in roots and differences in root architecture. 5.,The greater hydraulic efficiency of the non-sprouter life history type is attributed to its post-fire pioneering habit and may partially explain the relatively high speciation in the non-sprouters. Lower hydraulic efficiency is associated with a sprouting life history and greater shade tolerance. The seedling root systems represent a hydraulic bottleneck that may place roots under especially intense selection. [source] Genome-wide genetic diversity of Holstein Friesian cattle reveals new insights into Australian and global population variability, including impact of selectionANIMAL GENETICS, Issue 1 2007K. R. Zenger Summary Past breeding strategies for dairy cattle have been very effective in producing rapid genetic gain to achieve industry targets and raise profitability. Such gains have been largely facilitated by intense selection of sires combined with the use of artificial insemination. However, this practice can potentially limit the level of genetic diversity through inbreeding and selection plateaus. The rate of inbreeding in Australia is increasing, primarily as a result of semen importation from a small number of prominent bulls from the USA. The effect of this genetic influx in the Australian dairy cattle population is poorly understood both in terms of diversity and local adaptation/divergence. This study uses 845 genome-wide SNP genetic markers and 431 bulls to characterize the level of genetic diversity and genetic divergence within the Australian and international Holstein Friesian dairy population. No significant differences in genetic diversity (as measured by heterozygosity [Ho] and allelic richness [A]) were observed over the 25-year time period (1975,1999) for bulls used in Australia. The importation of foreign semen into Australia has increased the effective population size until it was in effect a sub-sample of the global population. Our data indicate that most individuals are equally closely related to one another, regardless of country of origin and year of birth. In effect, the global population can be considered as one single population unit. These results indicate that inbreeding, genetic drift and selection has had little effect at reducing genetic diversity and differentiating the Australian Holstein Friesian population at a genome-wide level. [source] Morphological and ecological responses to a conservation translocation of powan (Coregonus lavaretus) in ScotlandAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2010E. C. Etheridge Abstract 1.The establishment of refuge populations has become a common management tool for threatened fish species in recent years, yet the effects of translocation are not fully understood in a conservation context. 2.This paper examines the hypothesis that phenotypic changes have occurred during the formation of two refuge populations of the nationally rare powan (a freshwater fish species) which were established in Loch Sloy and Carron Valley Reservoir in Scotland. 3.Significant differences in head morphology, size and growth between the founder and refuge populations and between the two refuge populations were demonstrated. These changes are probably due to a combination of founder effects, intense selection and phenotypic plasticity. These changes can undermine the rationale behind the establishment of refuge populations. 4.The results call into question the usefulness of translocation as a conservation measure; however, there are times when this is the only viable management option available. The future of translocation and the validity of establishing refuge populations for powan conservation are discussed. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||