智利小植绥螨雄性对后代性别决定的影响

Many predatory mites in Phytoseiidae family are important natural enemies of small arthropod pests. They have a special mode of reproduction called pseudoarrhenotoky: both female and male offspring came from fertilized eggs, but the paternal genome in male offspring turned into heterochromatins and were eliminated. Therefore, males became haploid. Traditionally, sex allocation of Phytoseiidae were considered as precisely controlled by females, and eliminations of paternal genomes started soon after oviposition. However, some recent studies showed that offspring sex ratio matches reproductive strategies of the male parent instead of the female one, and heterochromatins were observed in spermatid development. Although data are quite limited, these results suggested the possibilities that males have significant impact on offspring sex allocation. In this study, we investigate the male influence on sex allocation in Phytoseiulus persimilis. Biology of this species has been best studied in Phytoseidae. We propose to observe heterochromatinization and paternal genome elimination in cells of multiple stages in spermatid and zygote development, using transmission electron microscope and fluorescence microscope, to achieve a systemic description of this process. The impact of prey density and age of males on spermatid quantity and form, and on offspring quantity and sex ratio will also be estimated. Results of this study will reveal critical periods of offspring sex allocation during male germline cells development, and evaluate male influence in offspring sex allocation. These results are important requirements for further explaining mechanisms of reproduction regulation in Phytoseiidae.

植绥螨科捕食螨是重要的小型有害生物天敌类群，其营特殊的假产雄孤雌生殖模式。即雌雄后代均从受精卵发育而来，但雄性后代因父系基因异染色质化后消失而发育成类单倍体。过去，植绥螨的后代性别决定被认为由雌螨精确调控，雄性后代父系基因的消失发生在卵产出后。近年来，一些研究发现植绥螨的后代性比可能符合雄性遗传策略而违背雌性遗传策略；且其父系染色体异质化发生时间很可能始于精子时期。由此推测雄性对后代性别决定可能存在影响，但尚缺乏针对这一问题的系统性研究。本项目选择植绥螨科中生物学研究较透彻的智利小植绥螨作为研究对象，一方面通过透射电镜与荧光显微镜观察精子及受精卵发育各阶段父系基因异染色质化与丢失程度，系统描述其发生过程；另一方面通过生物学实验定量分析雄螨对精子形态数量及后代性别的影响。通过本项目可明确雄性生殖系细胞发育过程中对后代性别决定起到关键作用的时期及其调控能力等，是深入解析生殖调控机理的必要前提。

植绥螨科捕食螨是重要的小型有害生物天敌类群，营特殊的假产雄孤雌生殖模式。即雌雄后代均从受精卵发育而来，但雄性后代因父系基因异染色质化后消失而发育成类单倍体。关注智利小植绥螨的雄性在后代性别调控中可能存在的影响较少。本项目选择植绥螨科中商品化历史最久、生物学研究较透彻的智利小植绥螨作为研究对象，描述了其雄性生殖系统结构、精包的产出及精子的形态和传递。生物学实验显示，智利小植绥螨雄螨在后代性比的调控中没有显著作用。不同年龄、营养状况的雄螨与雌螨交配后，后代性比没有显著变化。除非交配时间极短（15分钟），否则交配时长对后代的性比也没有显著影响。由此推测智利小植绥螨后代性比仍然主要由雌性调控。要进一步研究雄性后代中父系基因消失的过程，首先需要明确性别决定发生的时间及相关的调控机理。因此本项目对后续研究内容进行了调整，重点筛选了可能与生殖调控相关的基因，从中选择在昆虫性别调控中起到重要作用的transformer-2（tra-2）基因，通过RNA干扰法，明确了该基因在智利小植绥螨胚胎发育中起到重要作用，当这一基因被干扰后，卵的孵化率显著降低。其表达与调控的关键时期为雌成螨交配后第五天。以上工作为进一步分析tra-2关联基因、寻找性别决定调控基因打下了基础。