Malé P-J G, Leroy C, Humblot P, Dejean A, Quilichini A, Orivel J
Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
IRD, AMAP (botAnique et bioinforMatique de l'Architecture des Plantes), Montpellier Cedex, France.
J Evol Biol. 2016 Dec;29(12):2519-2529. doi: 10.1111/jeb.12980. Epub 2016 Oct 4.
Comparative studies of the population genetics of closely associated species are necessary to properly understand the evolution of these relationships because gene flow between populations affects the partners' evolutionary potential at the local scale. As a consequence (at least for antagonistic interactions), asymmetries in the strength of the genetic structures of the partner populations can result in one partner having a co-evolutionary advantage. Here, we assess the population genetic structure of partners engaged in a species-specific and obligatory mutualism: the Neotropical ant-plant, Hirtella physophora, and its ant associate, Allomerus decemarticulatus. Although the ant cannot complete its life cycle elsewhere than on H. physophora and the plant cannot live for long without the protection provided by A. decemarticulatus, these species also have antagonistic interactions: the ants have been shown to benefit from castrating their host plant and the plant is able to retaliate against too virulent ant colonies. We found similar short dispersal distances for both partners, resulting in the local transmission of the association and, thus, inbred populations in which too virulent castrating ants face the risk of local extinction due to the absence of H. physophora offspring. On the other hand, we show that the plant populations probably experienced greater gene flow than did the ant populations, thus enhancing the evolutionary potential of the plants. We conclude that such levels of spatial structure in the partners' populations can increase the stability of the mutualistic relationship. Indeed, the local transmission of the association enables partial alignments of the partners' interests, and population connectivity allows the plant retaliation mechanisms to be locally adapted to the castration behaviour of their symbionts.
对密切相关物种的群体遗传学进行比较研究，对于正确理解这些关系的演变是必要的，因为种群间的基因流动会在局部尺度上影响伙伴的进化潜力。因此（至少对于拮抗相互作用而言），伙伴种群遗传结构强度的不对称可能导致一方伙伴具有共同进化优势。在此，我们评估了参与物种特异性且 obligatory 互利共生关系的伙伴的群体遗传结构：新热带地区的蚁栖植物 Hirtella physophora 及其蚁类伙伴 Allomerus decemarticulatus。尽管这种蚂蚁无法在 H. physophora 以外的地方完成其生命周期，且该植物没有 A. decemarticulatus 提供的保护也无法长期存活，但这些物种也存在拮抗相互作用：已表明蚂蚁通过阉割其宿主植物而获益，且该植物能够对毒性过强的蚁群进行反击。我们发现这两个伙伴的扩散距离都很短，导致这种共生关系在当地得以延续，进而形成近亲繁殖的种群，在这种种群中，毒性过强的阉割蚁因缺乏 H. physophora 后代而面临当地灭绝的风险。另一方面，我们表明植物种群可能比蚂蚁种群经历了更大的基因流动，从而增强了植物的进化潜力。我们得出结论，伙伴种群中这种空间结构水平能够增加互利共生关系的稳定性。事实上，这种共生关系在当地的延续使得伙伴的利益部分趋于一致，且种群连通性使植物的反击机制能够在当地适应其共生体的阉割行为。
