Laboratory of Social Evolution and Behavior, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA; John Harvard Distinguished Science Fellowship Program, Harvard University, 52 Oxford Street, Cambridge, MA 02138, USA.
Laboratory of Social Evolution and Behavior, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA; Department of Organismic and Evolutionary Biology, Harvard University, 52 Oxford Street, Cambridge, MA 02138, USA.
Curr Biol. 2023 Mar 27;33(6):1047-1058.e4. doi: 10.1016/j.cub.2023.01.067. Epub 2023 Feb 28.
Most ant species have two distinct female castes-queens and workers-yet the developmental and genetic mechanisms that produce these alternative phenotypes remain poorly understood. Working with a clonal ant, we discovered a variant strain that expresses queen-like traits in individuals that would normally become workers. The variants show changes in morphology, behavior, and fitness that cause them to rely on workers in wild-type (WT) colonies for survival. Overall, they resemble the queens of many obligately parasitic ants that have evolutionarily lost the worker caste and live inside colonies of closely related hosts. The prevailing theory for the evolution of these workerless social parasites is that they evolve from reproductively isolated populations of facultative intermediates that acquire parasitic phenotypes in a stepwise fashion. However, empirical evidence for such facultative ancestors remains weak, and it is unclear how reproductive isolation could gradually arise in sympatry. In contrast, we isolated these variants just a few generations after they arose within their WT parent colony, implying that the complex phenotype reported here was induced in a single genetic step. This suggests that a single genetic module can decouple the coordinated mechanisms of caste development, allowing an obligately parasitic variant to arise directly from a free-living ancestor. Consistent with this hypothesis, the variants have lost one of the two alleles of a putative supergene that is heterozygous in WTs. These findings provide a plausible explanation for the evolution of ant social parasites and implicate new candidate molecular mechanisms for ant caste differentiation.
大多数蚂蚁物种都有两种截然不同的雌性等级——蚁后和工蚁——然而,产生这些替代表型的发育和遗传机制仍知之甚少。我们与一种克隆蚂蚁合作,发现了一种变体菌株,它在原本会成为工蚁的个体中表达出类似蚁后的特征。这些变体在形态、行为和适应性方面发生了变化,导致它们在野生型(WT)群体中依赖工蚁生存。总的来说,它们类似于许多专性寄生蚂蚁的蚁后,这些蚂蚁已经在进化中失去了工蚁等级,生活在与其密切相关的宿主群体中。对于这些没有工蚁的社会性寄生虫的进化,流行的理论是它们是从具有生殖隔离的兼性中间种群进化而来的,这些种群逐渐获得寄生表型。然而,对于这种兼性祖先的实证证据仍然薄弱,而且不清楚生殖隔离如何能在同域中逐渐出现。相比之下,我们在这些变体出现在其 WT 亲代群体后的少数几代内就将其分离出来,这意味着这里报道的复杂表型是在单个遗传步骤中诱导的。这表明,单个遗传模块可以分离出等级发育的协调机制,允许一种专性寄生变体直接从自由生活的祖先中产生。与这一假设一致的是,这些变体失去了 WT 中杂合的一个假定超级基因的两个等位基因之一。这些发现为蚂蚁社会性寄生虫的进化提供了一个合理的解释,并暗示了蚂蚁等级分化的新候选分子机制。