Sexual conflict reduces offspring fitness in zebra finches

Parental care is often costly; hence, in sexually reproducing species where both male and female parents rear their offspring (biparental care), sexual conflict over parental investment can arise. Such conflict occurs because each care-giver would benefit from withholding parental investment for use with another partner, leading to a reduction in the amount of care given by one parent at the expense of the other. Here we report experiments to explore the prediction from theory that parents rearing offspring alone may provide greater parental investment than when rearing offspring together with a partner. We found that when the number of offspring per parent, and hence the potential workload, were kept constant, offspring received a greater per capita parental investment from single females than from both parents working together, and that males reared by single mothers were more sexually attractive as adults than their biparentally reared siblings. This difference between single- and two-parent families is due to a reduction in care provided by females when they care together with a male, rather than laziness by males or differences in the begging behaviour of chicks, supporting the claim that sexual conflict in biparental care can reduce the quality of offspring raised.     

Highly fecund mothers sacrifice offspring survival to maximize fitness

Why do highly fecund organisms apparently sacrifice offspring size for increased numbers when offspring survival generally increases with size? The theoretical tools for understanding this evolutionary trade-off between number and size of offspring have developed over the past 25 years; however, the absence of data on the relation between offspring size and fitness in highly fecund species, which would control for potentially confounding variables, has caused such models to remain largely hypothetical. Here we manipulate egg size, controlling for maternal trait interactions, and determine the causal consequences of offspring size in a wild population of Atlantic salmon. The joint effect of egg size on egg number and offspring survival resulted in stabilizing phenotypic selection for an optimal size. The optimal egg size differed only marginally from the mean value observed in the population, suggesting that it had evolved mainly in response to selection on maternal rather than offspring fitness. We conclude that maximization of maternal fitness by sacrificing offspring survival may well be a general phenomenon among highly fecund organisms.     

Females increase offspring heterozygosity and fitness through extra-pair matings

Females in a variety of species commonly mate with multiple males, and there is evidence that they benefit by producing offspring of higher genetic quality; however, the nature of these genetic benefits is debated. Enhanced offspring survival or quality can result from intrinsic effects of paternal genes---'good genes'--or from interactions between the maternal and paternal genomes--'compatible genes'. Evidence for the latter process is accumulating: matings between relatives lead to decreased reproductive success, and the individual level of inbreeding--measured as average heterozygosity--is a strong fitness predictor. Females should thus benefit from mating with genetically dissimilar males. In many birds, social monogamy restricts mate choice, but females may circumvent this by pursuing extra-pair copulations. Here we show that female blue tits, Parus caeruleus, increase the heterozygosity of their progeny through extra-pair matings. Females thereby produce offspring of higher reproductive value, because less inbred individuals have increased survival chances, a more elaborate male secondary sexual trait (crown colour) and higher reproductive success. The cost of inbreeding may therefore be an important factor driving the evolution of female extra-pair mating.     

Female bluethroats enhance offspring immunocompetence through extra-pair copulations

Female birds frequently copulate with extra-pair males, but the adaptive value of this behaviour is poorly understood. Some studies have suggested that 'good genes' may be involved, where females seek to have their eggs fertilized by high-quality males without receiving any material benefits from them. Nevertheless, it remains to be shown that a genetic benefit is passed on to offspring. Here we report that nestling bluethroats, Luscinia svecica, sired by extra-pair males had a higher T-cell-mediated immune response than their maternal half-siblings raised in the same nest. The difference could not be attributed to nestling body mass, sex or hatching order, but may be an effect of paternal genotype. Extra-pair young were also more immunocompetent than their paternal half-sibs raised in the genetic father's own nest, which indicates an additional effect of maternal genotype. Our results are consistent with the idea that females engage in extra-pair copulations to obtain compatible viability genes, rather than 'good genes' per se.     

精氨酸对奶牛产雌率的影响

采用三种浓度（4．5％、5．5％和6．5％）的精氨酸对108头奶牛进行产母犊率试验．结果显示,试验组比对照组提高8．9％．13．34％,以5．5％精氨酸浓度最为明显,两者差异显著（P〈0．05）,而试验组之间差异不显著．在情期受胎率方面,试验组与对照组比较,试验组低于对照组,两者差异显著（P〈0．05）．     

对广州番禺职业技术学院学生体质健康测试结果的研究和分析

采用文献资料法、访谈调查法、数理统计等方法从各项目的测试成绩、变化趋势以及综合评价等方面．对广州番禺职业技术学院实施《国家学生体质健康标准》3年来的体质数据进行了深入分析，其目的是依其规律和趋势提出一些具有建设性的建议和对策，为高职院校体育教学改革实践提供理论上的支持，为提高大学生体质健康水平提供参考依据。     

Inclusive fitness in evolution

Arising from M. A. Nowak, C. E. Tarnita & E. O. Wilson 466, 1057-1062 (2010); Nowak et al. reply. For over fifty years, the evolution of social behaviour has been guided by the concept of inclusive fitness as a measure of evolutionary success. Nowak et al. argue that inclusive fitness should be abandoned. In so doing, however, they misrepresent the role that inclusive fitness has played in the theory of social evolution by which understanding social behaviour in a variety of disciplines has developed and flourished. By discarding inclusive fitness on the basis of its limitations, they create a conceptual tension which, we argue, is unnecessary, and potentially dangerous for evolutionary biology.     

女性文学流程与女性形象悖论

20世纪中国女性文学几经风雨 ,却愈来愈陷入了疲乏无力的状态中。在对女性文学流程的考察中 ,就女性文学这一衰微特征作了整体性评价 ,并由此提出了女性文学要走出这一误区 ,关键在于调整视界的建设性建议     

论关汉卿旦本剧中的女性认同意识

关剧中有许多身世悲惨、饱受社会压迫和折磨的女性形象,这表面上看是表现妇女的生活遭遇,实则隐喻了知识分子在当时的不公平待遇和政治遭遇;女性强烈的反抗意识代表了士阶层对黑暗、不公平现实的不满;女性依靠外力才能摆脱原有生存境遇的结局则与士阶层所遭受的禁锢、无出路契合。贯穿其中的对女性的认同意识是关汉卿大量创作旦本剧的原因和动力所在。     

改进适应值函数的遗传算法

比较、分析了几种基于适应值的选择策略求解极小值问题时的标准适应值函数,提出了一种随着进化代数的增加逐步增大适应值相互影响的标准适应值函数,并对它们的收敛速度和收敛精度进行了性能分析.以几个典型的函数优化问题为例进行仿真计算,取得了比较满意的结果.     

健美操专项课教学模式

在体育课教学中根据不同的教学规律,派生出不同的体育教学模式,各种模式都有其不同的功能和特性。以近年来健美操教学效果为依据,结合多年健美操教学经验,论述了高校健美操专项课的教学模式。     

女性意识在女性散文中的演进

20世纪女性散文具有现代性别意识与白话创作两个基本特征,体现了鲜明的文学现代性内涵.它真切地记载了女性意识在清末民初和五四时期觉醒、30-40年代走向成熟、50-70年代受到遮蔽及新时期以后不断深化几个重要的发展阶段,进而使女性散文成为百年中国女性由传统向现代生命历程的精神写照.     

《玉钏缘》的女性追求

明清之际的作品大多表现出对名节的追求,这与当时的社会背景密切相关.此时兴起的女性弹词作品与时代风尚紧密相连,女性心理、女子追求在作品中有充分表现.第一部由女性创作的弹词小说《玉钏缘》就是这方面的典范.     

Future fitness and helping in social queues

Helpers in primitively eusocial and cooperatively breeding animal societies forfeit their own reproduction to rear the offspring of a queen or breeding pair, but may eventually attain breeding status themselves. Kin selection provides a widely accepted theoretical framework for understanding these societies, but differences in genetic relatedness do not explain a universal societal feature: the huge variation between individuals in helping effort. An alternative explanation for this variation lies in a fundamental trade-off faced by helpers: by working harder, they increase the indirect component of their fitness, but simultaneously decrease their own future survival and fecundity. Here, we show that individuals work less hard when they stand to lose more future fitness through working. We experimentally manipulated two components of future fitness in social queues of hover wasps (Stenogastrinae): a helper's chance of inheriting an egg-laying position, and the workforce available to rear her offspring should she inherit. After each manipulation, helpers increased or decreased their effort as appropriate to the change in expected future fitness that they experienced. Although helping provides significant indirect fitness benefits for hover wasps, our study shows that variation in the costs associated with helping is the major determinant of helping effort.     

Transposable mating type genes in Saccharomyces cerevisiae.

A functional copy of the alpha mating type gene of Saccharomyces cerevisiae has been cloned by transformation in yeast. Using the Southern Blotting procedure it has been shown that three distinct genetic loci implicated in mating type interconversion (HML, HMR and MAT) contain sequences homologous to the clone fragment. The restriction fragment associated with each locus exhibits a characteristic size which can be correlated with the mating type allele present at that locus. The characteristic size difference between the a and alpha genetic elements made it possible to demonstrate that the homothallic interconversion of mating types in this yeast occurs by DNA rearrangement as proposed in the 'cassette hypothesis'.