Hardy Ian C W, Ode Paul J, Strand Michael R
Department of Population Biology, University of Leiden, P.O. Box 9516, 2300 RA, Leiden, The Netherlands.
Department of Entomology, University of Wisconsin-Madison, 53706, Madison, WI, USA.
Oecologia. 1993 Mar;93(3):343-348. doi: 10.1007/BF00317876.
Copidosoma sp. is a polyembryonic encyrtid wasp which parasitizes isolated hosts. Most broods of this wasp are unisexual, but some contain both sexes and the secondary sex ratio of these is usually highly female biased. The overall population secondary sex ratio is female biased. Walter and Clarke (1992) argue that because the majority of individuals must mate outside the natal patch, the bias in the population secondary sex ratio contradicts predictions made by Hamilton's (1967) theory of local mate competition (LMC). We suggest that the primary sex ratio is unbiased and that Walter and Clarke's results do not cast doubt on LMC. Instead these results imply that ovipositing females make a combined clutch size and sex ratio decision influencing whether individuals developing from a particular brood will outbreed or largely inbreed; for each case the predictions of LMC theory are not violated. If this interpretation is correct, what is of interest is the basis on which this decision is made rather than the population secondary sex ratio. We show that host encounter rate influences the proportions of mixed and single sex broods laid by Copidosoma floridanum, a related polyembryonic parasitoid. Among single-sex broods the primary sex ratio is female biased, but our results are in agreement with LMC theory since offspring developing from these broods will probably mate with siblings from adjacent hosts. We consider the egg load of females to be of major influence on oviposition behaviour, and that the mating structure of parasitoid offspring, potentially differential costs of male and female broods and the natural distributions of hosts both at oviposition and eclosion, require further study.
多胚跳小蜂是一种多胚的恩蚜小蜂，寄生于单个宿主。这种黄蜂的大多数蜂群是单性的，但有些包含两性，且这些蜂群的次生性别比通常高度偏向雌性。总体种群的次生性别比偏向雌性。沃尔特和克拉克（1992年）认为，由于大多数个体必须在出生地以外进行交配，种群次生性别比的偏差与汉密尔顿（1967年）的局部配偶竞争（LMC）理论的预测相矛盾。我们认为初生性别比是无偏差的，沃尔特和克拉克的结果并不质疑LMC理论。相反，这些结果意味着产卵的雌蜂会做出关于总产卵量和性别比的综合决定，这会影响从特定蜂群发育而来的个体是进行远系繁殖还是主要进行近交繁殖；在每种情况下，LMC理论的预测都没有被违反。如果这种解释是正确的，那么有趣的是做出这个决定的依据，而不是种群的次生性别比。我们表明，宿主遭遇率会影响佛罗里达多胚寄生蜂（一种相关的多胚寄生蜂）所产混合性别和单性别蜂群的比例。在单性别蜂群中，初生性别比偏向雌性，但我们的结果与LMC理论一致，因为从这些蜂群发育而来的后代可能会与相邻宿主的兄弟姐妹交配。我们认为雌蜂的卵负载对产卵行为有重大影响，而且寄生蜂后代的交配结构、雄蜂和雌蜂蜂群潜在的不同成本以及产卵时和羽化时宿主的自然分布都需要进一步研究。
