安徽省出生人口性别比失衡的现状及对策——基于第六次全国人口普查数据

自二十世纪八十年代中国政府实行计划生育政策后,安徽省出生人口性别比就开始出现失衡现象,这是多种因素综合产生的结果。它造成了人口结构的不合理,同时还严重影响婚姻市场的配对、人口再生产以及家庭和社会的和谐。必须采取加快经济发展步伐、建立健全社会保障体系、运用社会公共政策等措施来影响人们生育观念的转变,弱化人们的性别偏好,使出生性别比失衡从根本上得到解决。     

The optimal sex ratio in cooperatively breeding populations

In some cooperatively breeding species, elder siblings remain within their home ranges to assist their parents in raising their younger siblings by providing protection or food. Previous attempts to model the popu- lation sex ratios of such species have assumed that helping is cost-free and only involves benefits to parents, resulting in offspring sex ratio biases towards the helping sex. However, parents may also incur costs in maintaining helpers. We incorporated costs and benefits of helping to predict the sex ratio of offspring in a theoretical model. Our model showed that the evolutionary stable strategy （ESS） sex ratio strongly depends on three parameters： （1） the average number of helpers per female; （2） the benefits that a helper brings to its mother＇s offspring production （MOP）; and （3） the cost-benefit ratio of helping. When one sex of elder siblings provides help, the ESS sex ratio is biased towards the helping sex if MOP costs are less than the benefits, （i.e., the cost-benefit ratio 〈1）. However, the ESS sex ratio becomes biased towards the non-helping sex if MOP costs exceed the benefits （i.e., the cost-benefit ratio 〉1）. Additionally, our model shows that the ESS sex ratio becomes biased in favor of the more helpful sex when both male and female elder siblings provide help. These results explain why sex ratios may become biased towards the helping sex, as well as the non-helping sex, in some species.     

Population density affects sex ratio variation in red deer.

Many mammal populations show significant deviations from an equal sex ratio at birth, but these effects are notoriously inconsistent. This may be because more than one mechanism affects the sex ratio and the action of these mechanisms depends on environmental conditions. Here we show that the adaptive relationship between maternal dominance and offspring sex ratio previously demonstrated in red deer (Cervus elaphus), where dominant females produced more males, disappeared at high population density. The proportion of males born each year declined with increasing population density and with winter rainfall, both of which are environmental variables associated with nutritional stress during pregnancy. These changes in the sex ratio corresponded to reductions in fecundity, suggesting that they were caused by differential fetal loss. In contrast, the earlier association with maternal dominance is presumed to have been generated pre-implantation. The effects of one source of variation superseded the other within about two generations. Comparison with other ungulate studies indicates that positive associations between maternal quality and the proportion of male offspring born have only been documented in populations below carrying capacity.     

空间结构下性比率的稳定机制研究

分别利用基于个体的斑块占据模型（ IBM）和偶对近似方法（ PA）构造了一个空间结构下的两性集合种群模型,通过计算机仿真和数值模拟,研究了空间结构对性比率的稳定性的影响。结果表明：空间结构下由于Allee 效应的强作用,两性种群只有性比率维持稳定在1∶1附近时种群才能够续存;偶对近似方法可以很好的反映出元胞自动机的研究结果,这对进一步研究空间结构下两性集合种群的时空动态提供了有效的理论工具。     

液体抛撒初期水雾运动速度的实验研究

为研究比药量、长径比和水袋的厚度等因素对爆炸作用下液体抛撒初期水雾运动速度的影响,通过采用高速摄像技术拍摄了液体抛撒初期水雾形成的过程,分析了这些因素对爆炸作用下液体抛撒初期水雾运动速度的影响.结果表明:比药量、长径比和水袋的厚度等都是影响抛撒初期水雾运动速度的重要因素.     

Sperm competition: motility and the midpiece in primates

In animals with multiple-partner mating systems, the gametes of two or more males must compete to fertilize a given set of ova. Here we show that the volume of the midpiece in individual sperm is significantly greater in primate species in which the females mate with multiple partners, and in which males have larger testes in relation to their body weight, than in those species that mate with only one partner and have relatively small testes. Our results indicate that sexual selection by sperm competition has influenced the evolution of a specific component of male-gamete morphology, the volume of the sperm midpiece.