University of Guelph

About: University of Guelph is a education organization based out in Guelph, Ontario, Canada. It is known for research contribution in the topics: Population & Poison control. The organization has 26542 authors who have published 50553 publications receiving 1715255 citations. The organization is also known as: U of G & Guelph University.

Whiting events: Biogenic origin due to the photosynthetic activity of cyanobacterial picoplankton

Abstract: An annual whiting event occurs each year in late May to early June in Fayetteville Green Lake, New York. The initiation of this event correlates with exponential growth of the Synechococcus population within the lake. Synechococcus is the dominant (by approximately 4 orders of magnitude) autotrophic organism owing to the oligotrophic condition of the lake. The delta 13C values of the dissolved inorganic C range seasonally from -9.5% in winter to -6.2% in summer due to photosynthetic activity. Calcite precipitates principally in the microenvironment surrounding Synechococcus because of a photosynthetically driven alkalization process and the availability of the cells as nucleation sites. This calcite has a heavier delta 13C value (>4%) than does the dissolved inorganic C of the lake water owing to the cells' preferential uptake of 12C. A conceptual model suggests that photosynthetic activity and cell surface chemistry, together with the substantial surface area that arises from the great abundance of micron-sized cells, allow Synechococcus to dominate the annual whiting events in Fayetteville Green Lake.

The mismeasure of coping by checklist.

Abstract: Hundreds of studies have now used standardized checklists to assess respondents' self reports of coping with naturally occurring stress. This article presents a critical review of the conceptual and methodological issues involved in the use of these checklists. As they are currently employed, conventional checklists render an incomplete and distorted portrait of coping. Specifically, these checklists are grounded in too narrow a conception of coping; the application and interpretation of checklists in the typical study are not faithful to a transactional model of stress and coping; statistical controls cannot eliminate the effects of key person and situation variables on coping; and no consistent interpretation can be assigned to coping scale scores. Researchers are encouraged to consider a broader range of methods for assessing coping, including semistructured interviews, customized checklists tailored to their specific hypotheses and objectives, daily diaries, and traditional trait measures.

Reproductive isolation between autotetraploids and their diploid progenitors in fireweed, Chamerion angustifolium (Onagraceae)

Abstract: Summary Polyploidy is viewed as an important mechanism of sympatric speciation, but few studies have documented the reproductive barriers between polyploids and their diploid progenitors or explored the significance of assortative mating for polyploid establishment. Here we synthesize new and existing data on five prezygotic (geographic isolation, flowering asynchrony, pollinator fidelity, self-pollination, gametic selection) and two postzygotic (selection against triploid hybrids, inbreeding depression) reproductive barriers between diploid and autotetraploid individuals of the perennial plant Chamerion angustifolium. We also present estimates of realized rates of between-ploidy mating and examine the impact of assortative mating on polyploid dynamics using computer simulation. Reproductive isolation (measured from 0 to 1) was enforced by each barrier, including: geographic separation (RI = 0.41), flowering asynchrony (0.13), pollinator fidelity (0.85), self-pollination (0.44), gametic selection (0.44) and postzygotic isolation (0.87). Total reproductive isolation was 0.997, with the largest relative contributions by geography (41%) and pollinator fidelity (44%). Prezygotic barriers accounted for 97.6% isolation overall; however, tetraploids were more assortatively mating (98%) than diploids (79%). Realized reproductive isolation between ploidy levels in sympatric populations was 87% and tetraploids produced significantly fewer triploids than did diploids. Simulations indicated that the observed prezygotic isolation will reduce the strength of minority disadvantage acting on tetraploids and increase the importance of differences in viability and fertility between cytotypes in regulating polyploidy establishment.

The mechanisms of desiccation tolerance in developing seeds

Abstract: Desiccation tolerance is one of the most fundamental properties of seeds. It is acquired late in seed development and is considered necessary for the completion of the plant's life cycle, as an adaptive strategy to enable seed survival during storage or environmental stress, and to ensure better dissemination of the species. The role of water status in desiccated tissues and problems related to testing tolerance in seeds are reviewed. The molecular mechanisms of desiccation tolerance has received extensive consideration only during this past decade. There is a general consensus that desiccation tolerance involves the protection of cellular membranes from the deleterious effect of water removal and the resultant necessity to maintain the bilayer structure in the absence of an aqueous environment. Therefore, some aspects of desiccation-induced membrane injury are described. Several strategies for coping with cellular desiccation have been identified the presence of high amounts of non-reducing sugars, the efficiency of free radical-scavenging systems and the expression of desiccation- and/or ABA-regulated genes. These molecular mechanisms allowing cellular protection are reviewed together with their respective role in dessication tolerance. It is concluded that desiccation tolerance is not likely to be ascribed to a single mechanism but rather to a multifactorial property in which each component is equally critical.