Holzer Barbara, Keller Laurent, Chapuisat Michel
Department of Ecology and Evolution, University of Lausanne, Biophore, UNIL-Sorge, 1015 Lausanne, Switzerland.
BMC Evol Biol. 2009 Mar 31;9:69. doi: 10.1186/1471-2148-9-69.
Animal societies are diverse, ranging from small family-based groups to extraordinarily large social networks in which many unrelated individuals interact. At the extreme of this continuum, some ant species form unicolonial populations in which workers and queens can move among multiple interconnected nests without eliciting aggression. Although unicoloniality has been mostly studied in invasive ants, it also occurs in some native non-invasive species. Unicoloniality is commonly associated with very high queen number, which may result in levels of relatedness among nestmates being so low as to raise the question of the maintenance of altruism by kin selection in such systems. However, the actual relatedness among cooperating individuals critically depends on effective dispersal and the ensuing pattern of genetic structuring. In order to better understand the evolution of unicoloniality in native non-invasive ants, we investigated the fine-scale population genetic structure and gene flow in three unicolonial populations of the wood ant F. paralugubris.
The analysis of geo-referenced microsatellite genotypes and mitochondrial haplotypes revealed the presence of cryptic clusters of genetically-differentiated nests in the three populations of F. paralugubris. Because of this spatial genetic heterogeneity, members of the same clusters were moderately but significantly related. The comparison of nuclear (microsatellite) and mitochondrial differentiation indicated that effective gene flow was male-biased in all populations.
The three unicolonial populations exhibited male-biased and mostly local gene flow. The high number of queens per nest, exchanges among neighbouring nests and restricted long-distance gene flow resulted in large clusters of genetically similar nests. The positive relatedness among clustermates suggests that kin selection may still contribute to the maintenance of altruism in unicolonial populations if competition occurs among clusters.
动物社会多种多样，从小型的家族群体到非常庞大的社会网络，其中许多无亲缘关系的个体相互作用。在这个连续统一体的极端情况下，一些蚂蚁物种形成了单巢群体，其中工蚁和蚁后可以在多个相互连接的巢穴之间移动而不会引发攻击行为。虽然单巢性主要在入侵蚂蚁中得到研究，但它也存在于一些本地非入侵物种中。单巢性通常与非常高的蚁后数量相关，这可能导致巢内成员之间的亲缘关系水平极低，从而引发了在这样的系统中通过亲缘选择来维持利他行为的问题。然而，合作个体之间的实际亲缘关系关键取决于有效的扩散以及随之而来的遗传结构模式。为了更好地理解本地非入侵蚂蚁中单巢性的进化，我们研究了木蚁拟黑腹蚁三个单巢群体的精细尺度种群遗传结构和基因流。
对地理定位的微卫星基因型和线粒体单倍型的分析揭示了拟黑腹蚁三个群体中存在遗传分化巢穴的隐秘聚类。由于这种空间遗传异质性，同一聚类的成员有一定程度但显著的亲缘关系。核（微卫星）和线粒体分化的比较表明，所有群体中的有效基因流都是雄性偏向的。
这三个单巢群体表现出雄性偏向且大多是本地的基因流。每个巢穴中大量蚁后、相邻巢穴之间的交换以及有限的长距离基因流导致了大量遗传相似巢穴的聚类。聚类成员之间的正亲缘关系表明，如果在聚类之间发生竞争，亲缘选择可能仍然有助于维持单巢群体中的利他行为。
