Reuter M, Keller L
Institute of Ecology, University of Lausanne, 1015 Lausanne, Switzerland.
Am Nat. 2001 Aug;158(2):166-77. doi: 10.1086/321311.
The best known of the conflicts occurring in eusocial Hymenoptera is queen-worker conflict over sex ratio. So far, sex ratio theory has mostly focused on optimal investment in the production of male versus female sexuals, neglecting the investment in workers. Increased investment in workers decreases immediate sexual productivity but increases expected future colony productivity. Thus, an important issue is to determine the queen's and workers' optimal investment in each of the three castes (workers, female sexuals, and male sexuals), taking into account a possible trade-off between production of female sexuals and workers (both castes developing from diploid female eggs). Here, we construct a simple and general kin selection model that allows us to calculate the evolutionarily stable investments in the three castes, while varying the identity of the party controlling resource allocation (relative investment in workers, female sexuals, and male sexuals). Our model shows that queens and workers favor the investment in workers that maximizes lifetime colony productivity of sexual males and females, whatever the colony kin structure. However, worker production is predicted to be at this optimum only if one of the two parties has complete control over resource allocation, a situation that is evolutionarily unstable because it strongly selects the other party to manipulate sex allocation in its favor. Queens are selected to force workers to raise all the males by limiting the number of eggs they lay, whereas workers should respond to egg limitation by raising a greater proportion of the female eggs into sexual females rather than workers as a means to attain a more female-biased sex allocation. This tug-of-war between queens and workers leads to a stable equilibrium where sex allocation is between the queen and worker optima and the investment in workers is below both parties' optimum. Our model further shows that, under most conditions, female larvae are in strong conflict with queens and workers over their developmental fate because they value their own reproduction more than that of siblings. With the help of our model, we also investigate how variation in queen number and number of matings per queen affect the level of conflict between queens, workers, and larvae and ultimately the allocation of resource in the three castes. Finally, we make predictions that allow us to test which party is in control of sex allocation and caste determination.
在群居性膜翅目昆虫中，最为人所知的冲突是蜂王与工蜂在性别比例上的冲突。到目前为止，性别比例理论大多集中在雄性与雌性有性个体生产中的最优投资上，而忽略了对工蜂的投资。增加对工蜂的投资会降低当下的有性生殖生产力，但会提高预期的未来蜂群生产力。因此，一个重要的问题是，考虑到雌性有性个体和工蜂（这两个品级均由二倍体雌卵发育而来）生产之间可能存在的权衡，确定蜂王和工蜂在三个品级（工蜂、雌性有性个体和雄性有性个体）中的最优投资。在此，我们构建了一个简单通用的亲缘选择模型，该模型使我们能够计算在三个品级上的进化稳定投资，同时改变控制资源分配的一方的身份（对工蜂、雌性有性个体和雄性有性个体的相对投资）。我们的模型表明，无论蜂群的亲缘结构如何，蜂王和工蜂都倾向于对工蜂进行投资，以使有性的雄性和雌性的蜂群终身生产力最大化。然而，只有当双方中的一方完全控制资源分配时，工蜂的生产才预计处于这一最优状态，而这种情况在进化上是不稳定的，因为它会强烈地选择另一方操纵性别分配以利于自己。蜂王会通过限制工蜂产卵数量来迫使工蜂抚养所有的雄蜂，而工蜂则应通过将更大比例的雌卵培育为有性雌蜂而非工蜂来应对卵的限制，以此作为实现更偏向雌性的性别分配的一种手段。蜂王与工蜂之间的这种拉锯战导致了一种稳定的平衡，即性别分配处于蜂王和工蜂的最优值之间，且对工蜂的投资低于双方的最优值。我们的模型进一步表明，在大多数情况下，雌性幼虫在其发育命运上与蜂王和工蜂存在强烈冲突，因为它们更看重自身的繁殖而非同胞的繁殖。借助我们的模型，我们还研究了蜂王数量和每只蜂王交配次数如何影响蜂王、工蜂和幼虫之间的冲突程度，以及最终三个品级的资源分配。最后，我们做出了一些预测，这些预测使我们能够检验哪一方控制着性别分配和品级决定。
