Grangier Julien, Dejean Alain, Malé Pierre-Jean G, Orivel Jérôme
Laboratoire Evolution et Diversité Biologique, UMR-CNRS 5174, Université Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse cedex 9, France.
Naturwissenschaften. 2008 Oct;95(10):909-16. doi: 10.1007/s00114-008-0398-4. Epub 2008 May 22.
Although associations between myrmecophytes and their plant ants are recognized as a particularly effective form of protective mutualism, their functioning remains incompletely understood. This field study examined the ant-plant Hirtella physophora and its obligate ant associate Allomerus decemarticulatus. We formulated two hypotheses on the highly specific nature of this association: (1) Ant presence should be correlated with a marked reduction in the amount of herbivory on the plant foliage; (2) ant activity should be consistent with the "optimal defense" theory predicting that the most vulnerable and valuable parts of the plant are the best defended. We validated the first hypothesis by demonstrating that for ant-excluded plants, expanding leaves, but also newly matured ones in the long term, suffered significantly more herbivore damage than ant-inhabited plants. We showed that A. decemarticulatus workers represent both constitutive and inducible defenses for their host, by patrolling its foliage and rapidly recruiting nestmates to foliar wounds. On examining how these activities change according to the leaves' developmental stage, we found that the number of patrolling ants dramatically decreased as the leaves matured, while leaf wounds induced ant recruitment regardless of the leaf's age. The resulting level of these indirect defenses was roughly proportional to leaf vulnerability and value during its development, thus validating our second hypothesis predicting optimal protection. This led us to discuss the factors influencing ant activity on the plant's surface. Our study emphasizes the importance of studying both the constitutive and inducible components of indirect defense when evaluating its efficacy and optimality.
尽管蚁栖植物与其共生植物蚂蚁之间的关联被认为是一种特别有效的保护性互利共生形式,但其作用机制仍未被完全理解。这项实地研究考察了蚁栖植物多脉希氏樟(Hirtella physophora)及其专性共生蚂蚁十节全异蚁(Allomerus decemarticulatus)。我们针对这种关联的高度特异性提出了两个假设:(1)蚂蚁的存在应与植物叶片上食草动物的数量显著减少相关;(2)蚂蚁的活动应与“最优防御”理论一致,该理论预测植物最脆弱且最有价值的部分受到的防御最好。我们通过证明对于没有蚂蚁的植物,正在展开的叶片以及长期来看新成熟的叶片,比有蚂蚁栖息的植物遭受的食草动物损害要大得多,从而验证了第一个假设。我们表明,十节全异蚁工蚁通过在其叶片上巡逻并迅速召集巢友到叶片伤口处,为其宿主提供了组成型防御和诱导型防御。在研究这些活动如何根据叶片的发育阶段而变化时,我们发现随着叶片成熟,巡逻蚂蚁的数量急剧减少,而叶片伤口无论叶片年龄如何都会诱导蚂蚁聚集。这些间接防御的最终水平在叶片发育过程中大致与叶片的脆弱性和价值成正比,从而验证了我们预测最优保护的第二个假设。这使我们讨论了影响蚂蚁在植物表面活动的因素。我们的研究强调了在评估间接防御的功效和最优性时,研究其组成型和诱导型成分的重要性。