Antolin Michael F
Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA.
Department of Entomology, University of California, Riverside, Riverside, CA, 92521, USA.
Evolution. 1992 Oct;46(5):1496-1510. doi: 10.1111/j.1558-5646.1992.tb01140.x.
To understand genetic and phenotypic constraints on the sex ratio in a parasitic wasp that attacks fly pupae, I carried out a laboratory study of sex ratio variability in five strains of Muscidifurax raptor (Hymenoptera: Pteromalidae). I manipulated the environment through combinations of temperature and day length, and the numbers of females that attack a group of hosts. The change of phenotype in each strain over the range of environmental conditions describes the norm of each reaction for that strain, and measures how a strain responds to environmental variation to create phenotypic variability. Sex ratio in parasitic wasps is a complex trait that has several components-the numbers of eggs laid by an ovipositing wasp and the fraction of eggs that are fertilized (female). Further, sex ratio may be influenced by a female's reaction to other females exploiting the same hosts (superparasitism). I found no strain-environment interactions in either sex ratio or fecundity when I varied environmental conditions. Although strains differed in sex ratio and fecundity, all strains produced a more female-biased sex ratio and had higher fecundity when temperature and day length increased. Sex ratio and fecundity were phenotypically correlated, and strains with greater fecundity also produced a more female-biased sex ratio. All strains facultatively shifted sex ratio toward a higher fraction of males with increasing female density, despite apparent differences in superparasitism among strains. Males and females survived equally during development, so that mortality differences among strains and across environments could not account for sex ratio variability. This study indicates that sex ratio variability among strains is constrained by the correlation between sex ratio and fecundity, and that strains display similar facultative shifts in sex ratio as female density increases because sex ratio shifts are insensitive to differing levels of superparasitism.
为了解一种攻击蝇蛹的寄生蜂性别比例的遗传和表型限制因素，我对猛击蝇蛹小蜂（膜翅目：金小蜂科）的五个品系进行了性别比例变异性的实验室研究。我通过温度和日长的组合以及攻击一组寄主的雌蜂数量来操纵环境。每个品系在环境条件范围内的表型变化描述了该品系的每个反应规范，并衡量了一个品系如何响应环境变化以产生表型变异性。寄生蜂的性别比例是一个复杂的性状，有几个组成部分——产卵雌蜂产下的卵数以及受精卵（雌性）的比例。此外，性别比例可能受雌蜂对其他雌蜂利用同一寄主（重寄生）的反应影响。当我改变环境条件时，我在性别比例或繁殖力方面均未发现品系与环境的相互作用。尽管品系在性别比例和繁殖力方面存在差异，但当温度和日长增加时，所有品系都产生了更偏向雌性的性别比例且繁殖力更高。性别比例和繁殖力在表型上相关，繁殖力更高的品系也产生了更偏向雌性的性别比例。尽管品系间在重寄生方面存在明显差异，但随着雌蜂密度增加，所有品系都能使性别比例向更高比例的雄性转变。雄性和雌性在发育过程中的存活率相同，因此品系间和不同环境下的死亡率差异无法解释性别比例的变异性。这项研究表明，品系间的性别比例变异性受到性别比例与繁殖力之间相关性的限制，并且随着雌蜂密度增加，品系在性别比例上表现出相似的适应性转变，因为性别比例的转变对不同水平的重寄生不敏感。
