Department of Animal Ecology and Tropical Biology, University of Würzburg, Würzburg, Germany.
PLoS One. 2010 Oct 22;5(10):e13581. doi: 10.1371/journal.pone.0013581.
In populations of most social insects, gene flow is maintained through mating between reproductive individuals from different colonies in periodic nuptial flights followed by dispersal of the fertilized foundresses. Some ant species, however, form large polygynous supercolonies, in which mating takes place within the maternal nest (intranidal mating) and fertilized queens disperse within or along the boundary of the supercolony, leading to supercolony growth (colony budding). As a consequence, gene flow is largely confined within supercolonies. Over time, such supercolonies may diverge genetically and, thus, also in recognition cues (cuticular hydrocarbons, CHC's) by a combination of genetic drift and accumulation of colony-specific, neutral mutations.
METHODOLOGY/PRINCIPAL FINDINGS: We tested this hypothesis for six supercolonies of the invasive ant Anoplolepis gracilipes in north-east Borneo. Within supercolonies, workers from different nests tolerated each other, were closely related and showed highly similar CHC profiles. Between supercolonies, aggression ranged from tolerance to mortal encounters and was negatively correlated with relatedness and CHC profile similarity. Supercolonies were genetically and chemically distinct, with mutually aggressive supercolony pairs sharing only 33.1%±17.5% (mean ± SD) of their alleles across six microsatellite loci and 73.8%±11.6% of the compounds in their CHC profile. Moreover, the proportion of alleles that differed between supercolony pairs was positively correlated to the proportion of qualitatively different CHC compounds. These qualitatively differing CHC compounds were found across various substance classes including alkanes, alkenes and mono-, di- and trimethyl-branched alkanes.
We conclude that positive feedback between genetic, chemical and behavioural traits may further enhance supercolony differentiation through genetic drift and neutral evolution, and may drive colonies towards different evolutionary pathways, possibly including speciation.
在大多数社会性昆虫的种群中，基因流通过生殖个体在周期性婚飞中的交配来维持，这些个体来自不同的殖民地，随后进行传播。然而，一些蚂蚁物种形成了大型的多态超殖民地，在这种超殖民地中，交配发生在母巢内（巢内交配），受精后的蚁后在超殖民地内或沿着超殖民地的边界扩散，导致超殖民地的生长（ colony budding）。因此，基因流在很大程度上局限于超殖民地内部。随着时间的推移，这些超殖民地可能在遗传上发生分歧，从而在识别线索（表皮碳氢化合物，CHC）上也发生分歧，这是由遗传漂变和积累的与群体特异性相关的中性突变共同作用的结果。
方法/主要发现：我们在婆罗洲东北部的入侵蚂蚁 Anoplolepis gracilipes 的六个超殖民地中测试了这一假说。在超殖民地内，来自不同巢穴的工蚁相互容忍，亲缘关系密切，表现出高度相似的 CHC 谱。在超殖民地之间，攻击性从容忍到致命遭遇不等，与亲缘关系和 CHC 谱相似性呈负相关。超殖民地在遗传和化学上是不同的，具有相互攻击性的超殖民地对仅共享六个微卫星位点上 33.1%±17.5%（平均值±标准差）的等位基因和 CHC 谱中 73.8%±11.6%的化合物。此外，超殖民地对之间等位基因差异的比例与 CHC 化合物在质上的差异比例呈正相关。这些在质上不同的 CHC 化合物存在于各种物质类别中，包括烷烃、烯烃和单、二和三甲基支链烷烃。
我们得出结论，遗传、化学和行为特征之间的正反馈可能通过遗传漂变和中性进化进一步增强超殖民地的分化，并可能使殖民地走向不同的进化途径，包括可能的物种形成。
