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201.
A fundamental question concerning group-living species is what factors influence the evolution of sociality. Although several studies link adult social bonds to fitness, social patterns and relationships are often formed early in life and are also likely to have fitness consequences, particularly in species with lengthy developmental periods, extensive social learning, and early social bond-formation. In a longitudinal study of bottlenose dolphins (Tursiops sp.), calf social network structure, specifically the metric eigenvector centrality, predicted juvenile survival in males. Additionally, male calves that died post-weaning had stronger ties to juvenile males than surviving male calves, suggesting that juvenile males impose fitness costs on their younger counterparts. Our study indicates that selection is acting on social traits early in life and highlights the need to examine the costs and benefits of social bonds during formative life history stages.  相似文献   
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The possible conformations for the ABH and Lewis blood group oligosaccharides have been studied by an energy-minimisation procedure using empirical potential functions. It has been found that the conformation of the core structure is not altered significantly by the addition of l-fucose, galactose or N-acetyl galactosamine residues at the non-reducing end. Correlation of the preferred conformations with their known binding properties suggests that the differences between type 1 and type 2 structures become significant only when a large enough fragment of the determinant is considered. It is suggested that non-specific reagents may have small binding sites while the reagents that are specific for type 1 or type 2 structures may have larger binding sites. A two-pocket model has been proposed for antibodies and lectins which can distinguish the A1 and A2 antigens.  相似文献   
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ABSTRACT

The southern part of the Tamar valley area in SW England is highly mineralised and mines in the region were the world's principal producers of tin, copper and arsenic during the mid nineteenth century. The Devon Great Consols Mine, covering 67.6 ha (167 acres) is situated in this area. Residues from the mining activity resulted in unvegetated spoil tips and local soils highly contaminated with As (range 120–52600 μg/g As). Sequential chemical extraction procedures were conducted on eight surface samples (0–15 cm) taken from a 2.0 km long transect from within the mine site to agricultural grassland. The proportion of water extractable As in agricultural top soils was lower (0.05–0.3%) than the values obtained for mine wastes (0.02–1.2%). Arsenic was found to be concentrated in the Fe-organic and residual fractions, which accounted for up 93 % of the total As in mine spoil and nearby soils.  相似文献   
205.
Ammonium ion induces phenovariation in Gymnocolea inflata (Huds.) Dum. (Lophoziaceae) similar in nature to that induced in representatives of four other families of leafy liverworts by antagonists of hydroxyproline-protein metabolism. That is, in the presence of ammonium ion, ventral leaves developed and the lateral leaf morphology and the branching pattern of the plants changed. These changes, which reflect altered patterns of morphogenesis, were correlated with statistically significant (P ≥ 0.01) differences in peptidyl-hydroxyproline between normal and NH4+-induced phenovariant plants. The results support the hypothesis that cell wall-associated hydroxyproline-protein plays a morphoregulatory role and that any of a number of factors, genetic, epigenetic or environmental, that could alter the synthesis/distribution of this moiety could cause changes in form.  相似文献   
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We examined the combined effects of light and pCO2 on growth, CO2-fixation and N2-fixation rates by strains of the unicellular marine N2-fixing cyanobacterium Crocosphaera watsonii with small (WH0401) and large (WH0402) cells that were isolated from the western tropical Atlantic Ocean. In low-pCO2-acclimated cultures (190 ppm) of WH0401, growth, CO2-fixation and N2-fixation rates were significantly lower than those in cultures acclimated to higher (present-day ~385 ppm, or future ~750 ppm) pCO2 treatments. Growth rates were not significantly different, however, in low-pCO2-acclimated cultures of WH0402 in comparison with higher pCO2 treatments. Unlike previous reports for C. watsonii (strain WH8501), N2-fixation rates did not increase further in cultures of WH0401 or WH0402 when acclimated to 750 ppm relative to those maintained at present-day pCO2. Both light and pCO2 had a significant negative effect on gross : net N2-fixation rates in WH0402 and trends were similar in WH0401, implying that retention of fixed N was enhanced under elevated light and pCO2. These data, along with previously reported results, suggest that C. watsonii may have wide-ranging, strain-specific responses to changing light and pCO2, emphasizing the need for examining the effects of global change on a range of isolates within this biogeochemically important genus. In general, however, our data suggest that cellular N retention and CO2-fixation rates of C. watsonii may be positively affected by elevated light and pCO2 within the next 100 years, potentially increasing trophic transfer efficiency of C and N and thereby facilitating uptake of atmospheric carbon by the marine biota.  相似文献   
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Prostaglandin F (PGF) when administered to ovariectomized ewes by intra-carotid infusion did not alter either the pattern of tonic LH secretion or the LH surge evoked by estradiol, indicating that, in the sheep, the luteolytic action of PGF does not involve alteration of LH secretion by the pituitary gland.  相似文献   
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