Intrasexual competition and sexual selection in cooperative mammals

In most animals, the sex that invests least in its offspring competes more intensely for access to the opposite sex and shows greater development of secondary sexual characters than the sex that invests most. However, in some mammals where females are the primary care-givers, females compete more frequently or intensely with each other than males. A possible explanation is that, in these species, the resources necessary for successful female reproduction are heavily concentrated and intrasexual competition for breeding opportunities is more intense among females than among males. Intrasexual competition between females is likely to be particularly intense in cooperative breeders where a single female monopolizes reproduction in each group. Here, we use data from a twelve-year study of wild meerkats (Suricata suricatta), where females show high levels of reproductive skew, to show that females gain greater benefits from acquiring dominant status than males and traits that increase competitive ability exert a stronger influence on their breeding success. Females that acquire dominant status also develop a suite of morphological, physiological and behavioural characteristics that help them to control other group members. Our results show that sex differences in parental investment are not the only mechanism capable of generating sex differences in reproductive competition and emphasize the extent to which competition for breeding opportunities between females can affect the evolution of sex differences and the operation of sexual selection.     

Exocytotic fusion is activated by Rab3a peptides.

Studies of intracellular traffic in yeast and mammalian systems have implicated members of the Rab family of small GTP-binding proteins as regulators of membrane fusion. We have used the patch clamp technique to measure exocytotic fusion events directly and investigate the role of GTP-binding proteins in regulating exocytosis in mast cells. Intracellular perfusion of mast cells with GTP-gamma S is sufficient to trigger complete exocytotic degranulation in the absence of other intracellular messengers. Here we show that GTP is a potent inhibitor of GTP-gamma S-induced degranulation, indicating that sustained activation of a GTP-binding protein is sufficient for membrane fusion. We have found that synthetic oligopeptides, corresponding to part of the effector domain of Rab3a, stimulate complete exocytotic degranulation, similar to that induced by GTP-gamma S. The response is selective for Rab3a sequence and is strictly dependent on Mg2+ and ATP. This suggests that sustained activation of a Rab3 protein causes exocytotic fusion. The peptide response can be accelerated by GDP-beta S, suggesting that Rab3a peptides compete with endogenous Rab3 proteins for a binding site on a target effector protein, which causes fusion on activation.     

石棉对N，N－二甲基苯胺的吸附和氧化作用

研究了青石棉、温石棉、直闪石和铁石棉与不同浓度Ｎ，Ｎ－二甲基苯胺（ＤＭＡ）在１１０℃的吸附氧化反应，测定了产物的紫外可见光谱、红外光谱、元素分析和热分析数据．结果表明，四种石棉均能使ＤＭＡ氧化为甲基紫．质子可以提高石棉的氧化能力．此外，反应过程还生成一种紫外可见光最大吸收为３４０ｎｍ的物质，其结构有待进一步鉴定．     

Holocene lake deposits of Bosten Lake, southern Xinjiang, China

A 9.25-m-long sediment core from Bosten Lake,Xinjiang, provides detailed information about changes in the water budget and biological acticity over the last 8400 cal-endar years. The chronology is constructed from six AMS radiocarbon dates on the terrestrial plant remains. Based onanalyses of TOC, CO3, detrital compounds and biogenic SiO2,lake level fluctuations and periods of remarkably-negative water budget appeared at 8.4-8.2 cal ka, 7.38-7.25 cal ka,5.7-5.5 cal ka, 3.7-3.4 cal ka and 3.3-2.9 cal ka, respec-tively. As they are in-phase with low lake levels at Sumxl Co and Bangong Co in western Tibet Plateau and with paleo-lakes in Inner Mongolia, a climate-induced change to some-what drier and warmer conditions is inferred. A further drop in lake level after 1320 AD of about 200 yr duration may heattributed to a negative water balance prior to the main phase of the Little Ice Age. Deep and stable lake phases of 1500 yr and 1800 yr duration at 7.2-5.7 cal ka and 5.5-3.7cal ka coincide with maximum moisture during the Holocene Megathermai in China. The long term trend towards aridity since about 4.3 cal ka can dearly be recognised. The reduced water budget of Bosten Lake from 640-1200 AD may be attributed to local effects.     

A voltage-gated ion channel model inferred from the crystal structure of alamethicin at 1.5-A resolution

The crystal structure of alamethicin in nonaqueous solvent has been determined, and refined at 1.5-A resolution. The molecular conformation of the three crystallographically independent molecules is largely alpha-helical with a bend in the helix axis at an internal proline residue. The helix structure is highly amphipathic as most of the solvent-accessible polar atoms lie on a narrow strip of surface parallel to the helix axis. Molecular models for the voltage-gated ion channel, with n-fold symmetry and based on the molecular conformations observed in the crystal, are characterized by strong surface complementarity, a hydrophilic interior and a hydrophobic exterior. The channel structures are stabilized by a hydrated annulus of hydrogen-bonded glutamine residues which produce the greatest restriction in the channel diameter.     

Polygenic susceptibility to breast cancer and implications for prevention

The knowledge of human genetic variation that will come from the human genome sequence makes feasible a polygenic approach to disease prevention, in which it will be possible to identify individuals as susceptible by their genotype profile and to prevent disease by targeting interventions to those at risk. There is doubt, however, regarding the magnitude of these genetic effects and thus the potential to apply them to either individuals or populations. We have therefore examined the potential for prediction of risk based on common genetic variation using data from a population-based series of individuals with breast cancer. The data are compatible with a log-normal distribution of genetic risk in the population that is sufficiently wide to provide useful discrimination of high- and low-risk groups. Assuming all of the susceptibility genes could be identified, the half of the population at highest risk would account for 88% of all affected individuals. By contrast, if currently identified risk factors for breast cancer were used to stratify the population, the half of the population at highest risk would account for only 62% of all cases. These results suggest that the construction and use of genetic-risk profiles may provide significant improvements in the efficacy of population-based programs of intervention for cancers and other diseases.