title: Asymmetric interaction and indeterminate fitness correlation between cooperative partners in the fig-fig wasp mutualism.
abstract: 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.
authors.affiliation: State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Science, Kunming, Yunnan 650223, Republic of China. ruiwukiz@hotmail.com
authors.forename: Rui-Wu
authors.initials: RW
authors.lastname: Wang
authors.forename: Bao-Fa
authors.initials: BF
authors.lastname: Sun
authors.forename: Qi
authors.initials: Q
authors.lastname: Zheng
authors.forename: Lei
authors.initials: L
authors.lastname: Shi
authors.forename: Lixing
authors.initials: L
authors.lastname: Zhu
mesh_terms: D000818:Animals; D003163:Competitive Behavior; D030681:Ficus / Q000502:physiology*; D035264:Flowers; D005638:Fruit; D054817:Pollination; D011157:Population Dynamics; D013559:Symbiosis / Q000502:physiology*; D014863:Wasps / Q000502:physiology*