JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The preference of sheep for two temperate grassland species, ryegrass and white clover, was tested by releasing flocks (of three ewes) onto swards (0-25 ha) that contained adjacent monocultures of grass and clover, and observing their intake behaviour over 6 days. The test paddocks contained either 20, 50, or 80% clover by ground area to distinguish partial preference from indifference. 2. To test whether recent diet affected preference, separate groups of dry (nonpregnant, non-lactating) ewes grazed prior to testing on one of three diet 'backgrounds': an all-grass sward, an all-clover sward, or a 50:50 grass/clover sward by area. To consider the effects of physiological state on preference, a further group of lactating ewes, also from a 50:50 grass/clover 'background', were tested. 3. In all cases, the mean diet obtained was a mixture of grass and clover, even though greater intake rates would have been obtained eating pure clover. There was a consistent temporal pattern to preference, with ewes showing the greatest preference for clover in the morning. The results suggest that previous diet 'background' can have lasting effects on preference. Ewes that had been recently grazing monocultures initially showed an increased preference for the opposite species to the one they had been grazing. Over 6 days these animals gradually reverted to a preference for their 'background' diet. 4. Despite major differences in the energy requirement and intake behaviour of dry vs. lactating ewes, no significant effects of physiological state on preference were detected. Sheep grazing from swards of 20% clover spent a smaller proportion of time grazing clover and had a smaller proportion of clover in their diet than those grazing from 50% or 80% clover swards though, in all cases, behaviour was consistent with a preference for a high proportion of clover: sheep were not grazing at random. 5. Overall, the results demonstrate that sheep sustain a mixed diet even in situations where a monospecific diet is readily possible. Several alternative hypotheses to explain this (partial preference, novelty, rarity, 'sampling') are discussed. We suggest the results provide evidence of partial and changing preference by sheep. Our results urge caution in infering long-term grazing behaviour from short-term tests of preference and suggest why knowledge of diet preference even in common herbivores remains equivocal. Journal of Animal Ecology (1994) 63, 465-478 Diet preference of sheepanimal grazing unselectively could take its entire daily intake of dry matter from a few square m...

Purpose:To estimate the importance of respiratory and cardiac effects on signal variability found in functional magnetic resonance imaging data recorded from the brainstem. Materials and Methods:A modified version of the retrospective image correction (RETROICOR) method (Glover et al, [2000] Magn Reson Med 44:162-167) was implemented on resting brainstem echo-planar imaging (EPI) data in 12 subjects. Fourier series were fitted to image data based on cardiac and respiratory recordings (pulseoximetry and respiratory turbine), including multiplicative terms that accounted for interactions between cardiac and respiratory signals. F-tests were performed on residuals produced by regression analysis. Additionally, we evaluated whether modified RETROICOR improved detection of brainstem activation (in 11 subjects) during a finger opposition task. Results:The optimal model, containing three cardiac (C) and four respiratory (R) harmonics, and one multiplicative (X) term, "3C4R1X," significantly reduced signal variability without overfitting to noise. The application of modified RETROICOR to activation data increased group Z-statistics and reduced putative false-positive activation. Conclusion:In addition to cardiac and respiratory effects, their interaction was also a significant source of physiological noise. The modified RETROICOR model improved detection of brainstem activation and would be usefully applied to any study examining this brain region.

A previously described model of grass growth was used to analyse the effect of the severity of defoliation and the duration of the subsequent regrowth on the overall balance between photosynthesis, gross tissue production and leaf death and so on the amount that could be harvested/consumed per hectare under intermittent defoliation. Maximum yield per hectare was shown to be achieved whenever the fluctuations in LAI during regrowth and defoliation led lo the same low average LAI that was previously shown to give maximum yield (amount harvested/consumed per hectare) under continuous grazing. Thus, it is suggested that production under both continuous and intermittent defoliation may best be characterized, and diverse managements may be rationalized, on the basis of the average sward state, the average achieved. The analysis leads us to reconsider some widely held concepts of the growth and utilization of grass applied in both agronomic and ecological theory, and the provision of practical guidelines for management.

The unlimited proliferation of cancer cells requires a mechanism to prevent telomere shortening. Alternative Lengthening of Telomeres (ALT) is an homologous recombination-mediated mechanism of telomere elongation used in tumors, including osteosarcomas, soft tissue sarcoma subtypes, and glial brain tumors. Mutations in the ATRX/DAXX chromatin remodeling complex have been reported in tumors and cell lines that use the ALT mechanism, suggesting that ATRX may be an ALT repressor. We show here that knockout or knockdown of ATRX in mortal cells or immortal telomerase-positive cells is insufficient to activate ALT. Notably, however, in SV40-transformed mortal fibroblasts ATRX loss results in either a significant increase in the proportion of cell lines activating ALT (instead of telomerase) or in a significant decrease in the time prior to ALT activation. These data indicate that loss of ATRX function cooperates with one or more as-yet unidentified genetic or epigenetic alterations to activate ALT. Moreover, transient ATRX expression in ALT-positive/ATRX-negative cells represses ALT activity. These data provide the first direct, functional evidence that ATRX represses ALT.

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Substantial amounts of bone marrow edema at the pubic symphysis can occur in asymptomatic elite junior soccer players, but it is only weakly related to the development of osteitis pubis. Progressing training loads more slowly in athletes presenting with low current training loads may be a useful strategy for the prevention of osteitis pubis in junior soccer players.

S U M M A R YSeveral previous studies have shown that the proportion of clover in sheep diets was greater than the proportion of clover in the mixed species swards being grazed. Various hypotheses have been put forward to explain this observation. One widely held hypothesis is that sheep prefer (actively select) clover to grass. This hypothesis was tested by offering 12 sheep, six that had been recently grazing perennial ryegrass and six that had recently been grazing white clover, the choice between foraging on grass or clover provided as turves. It was found that, rather than prefer clover, the sheep preferred the opposite species to the one they had previously grazed. From these observations, alternative hypotheses are proposed to explain the disparity in composition of the diet relative to the swards observed in previous studies, and the evidence for a constant preference for clover and its basis in grazing behaviour is reconsidered.