The influence of host and non-host crops on the rhizobial population of the root rhizosphere

Non-Peer ReviewedField pea (Pisum sativum), a new crop to the Dark Brown and Black Chernozemic Soil Zones of Saskatchewan, forms a symbiosis with Rhizobium leguminosarum biovar viceae. This rhizobium is not native to the region, yet numbers in excess of 10^4 g-1 soil have been observed several years after a single inoculated field pea crop was grown. Modified immunoblot and ELISA techniques utilizing strain-specific polyclonal antibodies were used to monitor the environmental effect of host and non-host crop on rhizobial populations. The proportion of soil rhizobia able to nodulate pea differed between a competitive and poorly competitive isolate. Numbers of rhizobia declined over time in non-rhizosphere soil and increased in the presence of host plant. Both isolates maintained or increased soil populations from the initial level in the presence of certain non-host plants. The proportion of rhizobia available to nodulate a pea root increased more for the poorly competitive isolate in the presence of host and non-host root systems but did not reach the level of the highly competitive isolate

Optimization of hatchery culture of the sea scallop, Placopecten Magellanicus (Gmelin,1791) : dietary lipid quality and fatty acid requirements

Different species of live algal cultures varying broadly in essential fatty acid content - eicosapentaenoic acid (EPA; 20:5n-3), docosahexaenoic acid (DHA; 22:6n-3), and arachidonic acid (ARA; 20:4n-6) - were used in exploratory experiments to evaluate the impact of dietary lipid quality on broodstock conditioning and larval culture of the sea scallop (Placopecten magellanicus). Egg biochemical composition was relatively stable when diets were fed to animals in a partially conditioned state, but varied more for wild eggs compared to lab-conditioned animals. When diet treatments were initiated earlier in a second experiment, differences among the fatty acid composition of gonad samples were more apparent. -- In larval feeding trials, fatty acids in neutral lipids, and to lesser extent phospholipids, of larvae reflected the composition of the algae they were fed. C₂₀ and C₂₂ PUFA were preferentially accumulated, particularly DHA which plays a specific structural role in Pectinids. Growth results suggest increasing dietary ARA, or possibly 22:5n-6. -- Last, variability in lipid quality was examined in aging batch cultures of a strain of Pavlova sp. (CCMP459). Lipid, mainly TAG, as a proportion of dry weight, more than doubled over the experimental period. As cultures aged, the (n-3)/(n-6) series fatty acid ratio was reduced. By controlling algal harvest strategies or culture conditions, the biochemical composition of algae may be optimized to best meet the nutritional needs of a particular bivalve species or developmental stage

Comparative Brain Morphology of the Greenland and Pacific Sleeper Sharks and its Functional Implications

In cartilaginous fishes, variability in the size of the brain and its major regions is often associated with primary habitat and/or specific behavior patterns, which may allow for predictions on the relative importance of different sensory modalities. The Greenland (Somniosus microcephalus) and Pacific sleeper (S. pacificus) sharks are the only non-lamnid shark species found in the Arctic and are among the longest living vertebrates ever described. Despite a presumed visual impairment caused by the regular presence of parasitic ocular lesions, coupled with the fact that locomotory muscle power is often depressed at cold temperatures, these sharks remain capable of capturing active prey, including pinnipeds. Using magnetic resonance imaging (MRI), brain organization of S. microcephalus and S. pacificus was assessed in the context of up to 117 other cartilaginous fish species, using phylogenetic comparative techniques. Notably, the region of the brain responsible for motor control (cerebellum) is small and lacking foliation, a characteristic not yet described for any other large-bodied (\u3e3 m) shark. Further, the development of the optic tectum is relatively reduced, while olfactory brain regions are among the largest of any shark species described to date, suggestive of an olfactory-mediated rather than a visually-mediated lifestyle

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

We explore the behavior of a wormlike micellar solution under both steady and large amplitude oscillatory shear (LAOS) in a cone–plate geometry through simultaneous bulk rheometry and localized velocimetric measurements. First, particle image velocimetry is used to show that the shear-banded profiles observed in steady shear are in qualitative agreement with previous results for flow in the cone–plate geometry. Then under LAOS, we observe the onset of shear-banded flow in the fluid as it is progressively deformed into the non-linear regime—this onset closely coincides with the appearance of higher harmonics in the periodic stress signal measured by the rheometer. These harmonics are quantified using the higher-order elastic and viscous Chebyshev coefficients e [subscript n] and v [subscript n] , which are shown to grow as the banding behavior becomes more pronounced. The high resolution of the velocimetric imaging system enables spatiotemporal variations in the structure of the banded flow to be observed in great detail. Specifically, we observe that at large strain amplitudes (γ [subscript 0] ≥ 1), the fluid exhibits a three-banded velocity profile with a high shear rate band located in-between two lower shear rate bands adjacent to each wall. This band persists over the full cycle of the oscillation, resulting in no phase lag being observed between the appearance of the band and the driving strain amplitude. In addition to the kinematic measurements of shear banding, the methods used to prevent wall slip and edge irregularities are discussed in detail, and these methods are shown to have a measurable effect on the stability boundaries of the shear-banded flow.Spain. Ministerio de Educación y Ciencia (MEC) (Project FIS2010-21924-C02-02

Sensory Input Pathways and Mechanisms in Swallowing: A Review

Over the past 20 years, research on the physiology of swallowing has confirmed that the oropharyngeal swallowing process can be modulated, both volitionally and in response to different sensory stimuli. In this review we identify what is known regarding the sensory pathways and mechanisms that are now thought to influence swallowing motor control and evoke its response. By synthesizing the current state of research evidence and knowledge, we identify continuing gaps in our knowledge of these mechanisms and pose questions for future research

Survival of rhizobia in Saskatchewan soils as influenced by freeze/thaw cycling

Non-Peer ReviewedRhizobium leguminosarum biovar viceae are not native to Saskatchewan, but numbers of rhizobia in excess of l0^4 g-1 soil have been observed in fields previously grown to inoculated field pea (Pisum sativum L.). Modified immunoblot and ELISA techniques utilizing strain-specific polyclonal antibodies were used to monitor the survival of rhizobial populations under freeze/thaw conditions in field and controlled environment studies. Total rhizobial populations tended to decrease with each freeze/thaw cycle, but there were not always significant differences between pre- and post-freeze rhizobial populations. Total rhizobial numbers tended to be affected more by a fallow period then by the freeze/thaw cycle itself. The effect of soil moisture content at freezing on total populations varied with strain. The proportion of the total rhizobial population able to nodulate field pea was not affected by the freeze/thaw cycle, but a decrease during the fallow period was observed