有性生物的性别比例对于一个物种（种群）存活与发展具有决定性作用，因此性别比例的研究对种群生物学、进化生物学、以及生物育种等应用学科都具有至关重要的科学意义或启示。著名进化生物学家Hamilton以及Trivers 和Willard的理论认为：由于雄性在不同环境条件下对后代的贡献不同，尤其是当存在近亲交配和局域交配竞争等环境选择压力下，雄性的对后代的贡献率将因此而下降。物种将主动调节其性比，以提高其总的适合度。然而，项目申请人以著名的性比研究模式系统榕小蜂实验结果发现：榕小蜂并不能主动、量化地调节其性比，其性比在外界环境选择压力下，性比可能是通过遗传基因表达on-off机制实现调节。本项目将继续以榕小蜂为模式系统，在前期的工作基础上，进一步探讨什么环境选择压力、以及该压力通过什么具体机制导致榕小蜂的性比调节出现on-off的现象。

Sex ratio plays a critical role in both species survival and population maintainence for all of the sextual organisms. Therefore, the sex ratio regulating mechanisms will has a important implication in both theoretical and application biology,such as population biology, evolutionary biology, and reproduction biology. The well-known theory launched by distinguished evolutionary biologist Hamilton, Trivers and Willard, showed that the male might contribute to the gene frequency of offspring differently under varying environmental conditions. Namely, the gene frequency contribution of the male will decline under the increased pressure of environment selection, especially under the pressure of inbreeding and local mate competition. In such situation, the species will actively adjust their sex ratio to maximize their total fitness. However, our results based on the well documented fig-fig wasps system showed that, wasps cannot adjust the sex ratio of their offspring actively and quantitatively. We therfore hypothesized that the adjustment of fig wasps offspring's sex ratio might be triggered to active or not through the gene expression, a mechanism similar to the on-off of power switch. In this project, we will explore the biological machanism on-off adjustment of fig wasps and the related selection pressure.