In the fire ant Solenopsis invicta, a supergene composed of ~600 genes and having two variants, SB and Sb, regulates colony social form. In single queen colonies, all individuals carry only the SB allele, while in multiple queen colonies, some individuals carry the Sb allele. In this study, we characterized genes with copy number variation between SB and Sb-carrying individuals. We showed extensive acquisition of gene duplicates in the Sb genome, with some likely involved in polygyne-related phenotypes. We found 260 genes with copy number differences between SB and Sb, of which 239 have greater copy number in Sb. We observed transposable element (TE) accumulation on Sb, likely due to the accumulation of repetitive elements on the nonrecombining chromosome. We found a weak correlation between TE copy number and differential expression, suggesting some TEs may still be proliferating in Sb while many of the duplicated TEs have presumably been silenced. Among the 115 non-TE genes with higher copy in Sb, enzymes responsible for cuticular hydrocarbon synthesis were highly represented. These include a desaturase and an elongase, both potentially responsible for differential queen odour and likely beneficial for polygyne ants. These genes seem to have translocated into the supergene from other chromosomes and proliferated by multiple duplication events. While the presence of TEs in supergenes is well documented, little is known about duplication of non-TE genes and their possible adaptive role. Overall, our results suggest that gene duplications may be an important factor leading to monogyne and polygyne ant societies.

中文翻译：

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火蚁社交超基因的特征在于广泛的基因和转座因子拷贝数变异。

在火蚁Solenopsis invicta中，一种由约600个基因组成的超基因，具有两个变种SB和Sb，可调节菌落的社会形态。在单个皇后菌落中，所有个体仅携带SB等位基因，而在多个皇后菌落中，一些个体携带Sb等位基因。在这项研究中，我们表征了携带SB和Sb的个体之间拷贝数变异的基因。我们显示了广泛获得的Sb基因组中的基因重复，其中一些可能与polygyne相关的表型有关。我们发现260个基因在SB和Sb之间具有拷贝数差异，其中239个基因在Sb中具有更大的拷贝数。我们观察到Sb上的转座因子（TE）积累，可能是由于非重组染色体上的重复元素积累所致。我们发现TE拷贝数与差异表达之间的相关性很弱，这表明一些TE可能仍在Sb中扩散，而许多重复的TE可能已被沉默了。在Sb中具有较高拷贝的115个非TE基因中，负责表皮碳氢化合物合成的酶被高度代表。这些包括去饱和酶和延伸酶，它们既可能导致不同的女王气味，也可能对多妇科蚂蚁有益。这些基因似乎已从其他染色体转移到超基因中，并因多次复制事件而增殖。尽管在超基因中存在TE的文献充分记载，但对于非TE基因的复制及其可能的适应性作用知之甚少。总体而言，我们的研究结果表明基因重复可能是导致单性生殖和多性生殖蚂蚁社会的重要因素。