Pedersen Jes S, Krieger Michael J B, Vogel Valérie, Giraud Tatiana, Keller Laurent
Department of Ecology and Evolution, University of Lausanne, Biophore, CH-1015 Lausanne, Switzerland.
Evolution. 2006 Apr;60(4):782-91.
Kinship among group members has long been recognized as a main factor promoting the evolution of sociality and reproductive altruism, yet some ants have an extraordinary social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This type of social organization is not only a key attribute responsible for the ecological dominance of these ants, but also an evolutionary paradox because relatedness between nestmates is effectively zero. Recently, it has been proposed that, in the Argentine ant, unicoloniality is a derived trait that evolved after its introduction into new habitats. Here we test this basic assumption by conducting a detailed genetic analysis of four native and six introduced populations with five to 15 microsatellite loci and one mitochondrial gene. In contrast to the assumption that native populations consist of family-based colonies with related individuals who are aggressive toward members of other colonies, we found that native populations also form supercolonies, and are effectively unicolonial. Moreover, just as in introduced populations, the relatedness between nestmates is not distinguishable from zero in these native range supercolonies. Genetic differentiation between native supercolonies was very high for both nuclear and mitochondrial markers, indicating extremely limited gene flow between supercolonies. The only important difference between the native and introduced populations was that supercolonies were several orders of magnitude smaller in the native range (25-500 m). This size difference has important consequences for our understanding of the evolution and stability of unicolonial structures because the relatively small size of supercolonies in the native range implies that competition can occur between supercolonies, which can act as a break on the spread of selfish mutants by eliminating supercolonies harboring them.
群体成员之间的亲缘关系长期以来一直被认为是促进社会性和生殖利他主义进化的主要因素，然而一些蚂蚁具有一种非凡的社会组织，称为单巢性，即个体在物理上分离的巢穴之间自由混合。这种社会组织类型不仅是这些蚂蚁在生态上占据优势的关键属性，也是一个进化悖论，因为同巢伙伴之间的亲缘关系实际上为零。最近，有人提出，在阿根廷蚂蚁中，单巢性是一种衍生特征，是在其被引入新栖息地后进化而来的。在这里，我们通过对四个本地种群和六个引入种群进行详细的遗传分析来检验这一基本假设，使用了5到15个微卫星位点和一个线粒体基因。与本地种群由基于家族的群体组成，群体内个体具有亲缘关系且对其他群体成员具有攻击性这一假设相反，我们发现本地种群也形成超级群体，并且实际上是单巢性的。此外，就像在引入种群中一样，在这些本地范围内的超级群体中，同巢伙伴之间的亲缘关系与零没有区别。对于核标记和线粒体标记，本地超级群体之间的遗传分化都非常高，这表明超级群体之间的基因流动极其有限。本地种群和引入种群之间唯一重要的区别是，本地范围内的超级群体规模要小几个数量级（25 - 500米）。这种规模差异对于我们理解单巢结构的进化和稳定性具有重要意义，因为本地范围内超级群体相对较小的规模意味着超级群体之间可能会发生竞争，这可以通过消除携带自私突变体的超级群体来抑制自私突变体的传播。
