Ferdy Jean-Baptiste, Després Laurence, Godelle Bernard
CC 63, Laboratoire Génome, populations, interactions, Université Montpellier II, F-34095, Montpellier, Cedex 05, France.
J Theor Biol. 2002 Jul 21;217(2):219-34. doi: 10.1006/jtbi.2002.3018.
Plant/seed-eater pollinators mutualisms involve a plant pollinated by an insect whose larvae develop by eating a fraction of host-plant seeds. The outcome of the interaction therefore depends on the number of ovules fertilized by adult visits and the number of seeds destroyed by larvae. Among the very few cases of such mutualisms reported so far is the globeflower-globeflower flies mutualism, which is unique in that it involves several congeneric fly species (Chiastocheta genus) coexisting within a single host-plant species, Trollius europaeus. These species exhibit contrasted oviposition behaviors resulting in a more or less beneficial outcome for the plant. We designed an adaptive dynamics model to investigate how morphological traits of globeflower could affect the evolution of oviposition in its pollinating flies. Three fly traits (flower age at oviposition, clutch size and the level of avoidance of already parasitized flowers) and one plant trait (closed or open corolla) were examined. Whatever the shape of the flower, evolutionary branching occurs between early and late ovipositing flies, driven by strong competition among larvae within a fruit. Once this branching occurred, the closed shape of the corolla is likely to offer a better protection to eggs of early but not of late ovipositing flies. The difference in egg survival results in higher competition among early larvae and thus selects for decreased clutch size in early flies. This can be seen as a first step in the evolution of a mutualistic behavior. The prediction of our model fits field observations of fly behavior, giving theoretical support to the hypothesis of fly sympatric speciation within its host plant. Moreover, flower closed globe shape can be positively selected in globeflowers as it results in a reduction of parasitism strength. This last evolution therefore leads to a stable mutualism between globeflowers and globeflower flies.
以植物/种子为食的传粉者共生关系涉及一种由昆虫传粉的植物，该昆虫的幼虫通过食用一部分寄主植物种子来发育。因此，这种相互作用的结果取决于成年昆虫访花受精的胚珠数量以及幼虫破坏的种子数量。到目前为止，报道的这种共生关系的案例非常少，其中之一是金莲花-金莲花蝇共生关系，其独特之处在于它涉及几种同属的蝇类物种（Chiastocheta属）在单一寄主植物欧洲金莲花（Trollius europaeus）中共存。这些物种表现出不同的产卵行为，从而对植物产生或多或少有益的结果。我们设计了一个适应性动态模型来研究金莲花的形态特征如何影响其传粉蝇产卵行为的进化。研究了三种蝇类特征（产卵时的花龄、一窝卵的数量以及对已被寄生花朵的回避程度）和一种植物特征（花冠闭合或开放）。无论花的形状如何，由于果实内幼虫之间的激烈竞争，在早产卵蝇和晚产卵蝇之间都会发生进化分支。一旦这种分支发生，花冠的闭合形状可能会为早产卵蝇的卵提供更好的保护，而对晚产卵蝇的卵则不然。卵存活率的差异导致早龄幼虫之间的竞争加剧，从而选择降低早产卵蝇一窝卵的数量。这可以被视为互利行为进化的第一步。我们模型的预测与蝇类行为的实地观察结果相符，为蝇类在其寄主植物内同域物种形成的假设提供了理论支持。此外，金莲花中花冠闭合的球形形状可以被正向选择，因为它会降低寄生强度。因此，这最后的进化导致了金莲花和金莲花蝇之间稳定的共生关系。
