不同建群蜂数对肿腿蜂子代性比的影响

Effects of Different Foundress Densities on Sex Ratio of the Offspring of Bethylid Wasps

【目的】性比可调节是寄生蜂一种很常见的生物学现象。局部配偶竞争理论认为偏雌性比是大多数群居型寄生蜂的进化稳定策略,而当建群蜂数量增加时,这种偏雌性比才会被打破并趋于雌雄均等。肿腿蜂是天牛和吉丁虫类等林木蛀干害虫的重要天敌,其性比结构是保障生防效率的基础。为了明晰肿腿蜂的性比结构,探明改变建群蜂数量是否会促使肿腿蜂调节其性比,并同时探究局部配偶竞争模型是否适用于预测肿腿蜂类寄生蜂的性比。【方法】本研究选择管氏肿腿蜂、白蜡吉丁肿腿蜂和松墨天牛肿腿蜂为试验对象,分析了当建群蜂数分别为1~8头时其子代性比和单雌子代数的变化规律,比较了3种肿腿蜂在不同建群蜂密度下的实测性比与基于局部配偶竞争模型的预测性比的差异。【结果】3种肿腿蜂均为高度偏雌性比。子代雄性比随建群蜂数量增加有一定幅度的升高。增加建群蜂的数量使单雌平均子代数减少,单雌平均子代数与雄性比呈显著负相关。1~8头建群蜂数下,3种肿腿蜂实测性比均低于10%,与局部配偶竞争模型的性比预测值偏离较大。【结论】肿腿蜂的偏雌性比是一种进化稳定的特征,当建群蜂数量增加时,子代雄性比会呈小幅增加,但高度偏雌的性比不会因建群蜂数量的增加而被均衡化。局部配偶竞争模型不能准确地反映肿腿蜂在不同建群蜂数量下的性比变化规律。

【Objective】Sex ratio adjustability is a widespread ecological phenomenon in parasitic wasps.A female-biased sex ratio has long been asserted as the evolutionary stable strategy for some gregarious parasitic wasps on account of the theory of local mate competition(LMC).This evolutionary stable sex ratio can only be equalized as the increasing of foundresses numbers.The bethylid wasps have been widely used as biocontrol agents for several cerambycid and buprestid larvae,and their sex ratio structures are the basis of biocontrol.This study aims to clarify the sex ratios of the bethylid wasps and to prove whether the LMC model was applicable to the prediction of their sex ratios under different foundress densities.【Method】In this study,Sclerodermus guani,S.pupariae,and S.alternatusi were selected as the experimental objects.The changes of offspring sex ratio and the brood size per female of three bethylid wasps were analyzed when the foundress densities ranged from one to eight respectively.The measured sex ratio of these three parasitoids and their predicted sex ratio based on LMC model under different foundress densities were comparatively studied.【Result】The results indicated that the sex ratio of these three parasitoids were highly female-biased.Brood size per foundress significantly reduced when the numbers of foundress increased from one to eight.The sex ratio of these bethylid parasitoids exhibited slightly increase with the increasing foundress densities and negatively related to the brood size per foundress.Meanwhile,the predicted sex ratios based on the LMC model of these bethylid parasitoids deviated significantly from their measured sex ratios.【Conclusion】The extremely female-biased sex ratio is an evolutionary stable biological characteristic for the bethylid parasitoids.This female bias of the bethylid parasitoids cannot be equalized,even though it would become a slightly less biased,with increasing numbers of foundress.The LMC model cannot accurately reflect the fluctuations of bethylid sex ratio under different foundress densities.