Loeb M L G, Zink A G
Center for Population Biology, Section of Evolution and Ecology, University of California at Davis, CA 95616, USA.
J Evol Biol. 2006 May;19(3):889-99. doi: 10.1111/j.1420-9101.2005.01044.x.
Individuals within complex social groups often experience reduced reproduction owing to coercive or suppressive actions of other group members. However, the nature of social and ecological environments that favour individual acceptance of such costs of sociality is not well understood. Taxa with short periods of direct social interaction, such as some communal egg layers, are interesting models for study of the cost of social interaction because opportunities to control reproduction of others are limited to brief periods of reproduction. To understand the conditions under which communal egg layers are in fitness conflict and thus likely to influence each other's reproduction, we develop an optimality model involving a brood guarding 'host' and a nonguarding disperser, or 'egg dumper'. The model shows that when, where intermediate-sized broods have highest survival, lifetime inclusive fitnesses of hosts and dumpers are often optimized with different numbers of dumped eggs. We hypothesize that resolution of this conflict may involve attempts by one party to manipulate the other's reproduction. To test model predictions we used a lace bug (Heteroptera: Tingidae) that shows both hosts and egg dumpers as well as increased offspring survival in response to communal egg laying. We found that egg-dumping lace bugs oviposit a number of eggs that very closely matches predicted fitness optimum for hosts rather than predicted optimum of dumpers. This result suggests that dumpers pay a social cost for communal egg laying, a cost that may occur through host suppression of dumper reproduction. Although dumper allocation of eggs is thus sub-optimal for dumpers, previous models show that the decision to egg dump is nevertheless evolutionarily stable, possibly because hosts permit just enough dumper oviposition to encourage commitment to the behaviour.
在复杂的社会群体中，个体的繁殖往往会因其他群体成员的强制或抑制行为而减少。然而，有利于个体接受这种社会性代价的社会和生态环境的本质尚未得到很好的理解。具有短暂直接社会互动的生物类群，如一些共同产卵者，是研究社会互动代价的有趣模型，因为控制其他个体繁殖的机会仅限于短暂的繁殖期。为了理解共同产卵者在适合度冲突中并因此可能相互影响繁殖的条件，我们开发了一个最优模型，该模型涉及一个守护巢穴的“宿主”和一个不守护巢穴的扩散者，即“弃卵者”。该模型表明，当中间大小的巢穴具有最高存活率时，宿主和弃卵者的终生广义适合度通常会通过不同数量的弃卵而达到最优。我们假设这种冲突的解决可能涉及一方试图操纵另一方的繁殖。为了检验模型预测，我们使用了一种网蝽（半翅目：网蝽科），它既表现出宿主和弃卵者，也表现出共同产卵会增加后代存活率。我们发现，弃卵的网蝽产卵数量与预测的宿主适合度最优值非常接近，而不是预测的弃卵者最优值。这一结果表明，弃卵者为共同产卵付出了社会代价，这种代价可能是通过宿主抑制弃卵者繁殖而产生的。因此，尽管弃卵者的卵分配对其自身而言并非最优，但先前的模型表明，弃卵的决定在进化上仍然是稳定的，这可能是因为宿主允许弃卵者进行足够的产卵，以鼓励其坚持这种行为。
