State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Science, Kunming, Yunnan 650223, Republic of China.
J R Soc Interface. 2011 Oct 7;8(63):1487-96. doi: 10.1098/rsif.2011.0063. Epub 2011 Apr 13.
Empirical observations have shown that cooperative partners can compete for common resources, but what factors determine whether partners cooperate or compete remain unclear. Using the reciprocal fig-fig wasp mutualism, we show that nonlinear amplification of interference competition between fig wasps-which limits the fig wasps' ability to use a common resource (i.e. female flowers)-keeps the common resource unsaturated, making cooperation locally stable. When interference competition was manually prevented, the fitness correlation between figs and fig wasps went from positive to negative. This indicates that genetic relatedness or reciprocal exchange between cooperative players, which could create spatial heterogeneity or self-restraint, was not sufficient to maintain stable cooperation. Moreover, our analysis of field-collected data shows that the fitness correlation between cooperative partners varies stochastically, and that the mainly positive fitness correlation observed during the warm season shifts to a negative correlation during the cold season owing to an increase in the initial oviposition efficiency of each fig wasp. This implies that the discriminative sanction of less-cooperative wasps (i.e. by decreasing the egg deposition efficiency per fig wasp) but reward to cooperative wasps by fig, a control of the initial value, will facilitate a stable mutualism. Our finding that asymmetric interaction leading to an indeterminate fitness interaction between symbiont (i.e. cooperative actors) and host (i.e. recipient) has the potential to explain why conflict has been empirically observed in both well-documented intraspecific and interspecific cooperation systems.
实证观察表明，合作的伙伴可以争夺共同的资源，但决定伙伴是合作还是竞争的因素尚不清楚。利用互惠的榕小蜂-榕果共生关系，我们表明榕小蜂之间的干扰竞争呈非线性放大，这限制了榕小蜂利用共同资源（即雌性花）的能力，使共同资源不饱和，从而使合作在局部保持稳定。当干扰竞争被人为阻止时，榕果和榕小蜂之间的适合度相关性从正相关变为负相关。这表明，合作参与者之间的遗传关联性或互惠交换，可能会产生空间异质性或自我约束，但不足以维持稳定的合作。此外，我们对实地收集的数据进行分析，发现合作伙伴之间的适合度相关性是随机变化的，在温暖季节观察到的主要正相关关系在寒冷季节因每个榕小蜂的初始产卵效率增加而转变为负相关。这意味着，对不太合作的小蜂进行歧视性制裁（即通过减少每只榕小蜂在榕果上的产卵效率），但榕果对合作小蜂的奖励，通过控制初始值，将有助于稳定的共生关系。我们的发现表明，不对称的相互作用导致共生体（即合作的行为者）和宿主（即接受者）之间不确定的适合度相互作用，这有可能解释为什么在有充分记录的种内和种间合作系统中都观察到了冲突。
