Radford Julianne M, Chen David, Chernyshova Anna M, Taylor Cambrie, Guoth Alex W, Wu Tian, Hill Kathleen A, Thompson Graham J
Department of Biology, Western University, London, ON N6A 5B7, Canada.
Insects. 2022 Feb 24;13(3):224. doi: 10.3390/insects13030224.
Analyzing the information-rich content of RNA can help uncover genetic events associated with social insect castes or other social polymorphisms. Here, we exploit a series of cDNA libraries previously derived from whole-body tissue of different castes as well as from three behaviourally distinct populations of the Eastern subterranean termite Reticulitermes flavipes. We found that the number (0.5 M) of single nucleotide variants (SNVs) was roughly equal between nymph, worker and soldier caste libraries, but dN/dS (ratio of nonsynonymous to synonymous substitutions) analysis suggested that some of these variants confer a caste-specific advantage. Specifically, the dN/dS ratio was high (4.3) for genes expressed in the defensively specialized soldier caste, relative to genes expressed by other castes (~1.7−1.8) and regardless of the North American population (Toronto, Raleigh, Boston) from which the castes were sampled. The populations, meanwhile, did show a large difference in SNV count but not in the manner expected from known demographic and behavioural differences; the highly invasive unicolonial population from Toronto was not the least diverse and did not show any other unique substitution patterns, suggesting any past bottleneck associated with invasion or with current unicoloniality has become obscured at the RNA level. Our study raises two important hypotheses relevant to termite sociobiology. First, the positive selection (dN/dS > 1) inferred for soldier-biased genes is presumably indirect and of the type mediated through kin selection, and second, the behavioural changes that accompany some social insect urban invasions (i.e., ‘unicoloniality’) may be detached from the loss-of-diversity expected from invasion bottlenecks.
分析RNA丰富的信息内容有助于揭示与社会性昆虫等级或其他社会多态性相关的遗传事件。在这里，我们利用了一系列先前从不同等级的全身组织以及来自东部地下白蚁黄胸散白蚁（Reticulitermes flavipes）三个行为不同的群体中获得的cDNA文库。我们发现，若虫、工蚁和兵蚁等级文库中的单核苷酸变异（SNV）数量（约0.5M）大致相等，但非同义替换与同义替换比率（dN/dS）分析表明，其中一些变异具有等级特异性优势。具体而言，相对于其他等级（约1.7 - 1.8）表达的基因，在防御特化的兵蚁等级中表达的基因的dN/dS比率较高（约4.3），且与所采样等级来自的北美群体（多伦多、罗利、波士顿）无关。与此同时，这些群体在SNV数量上确实存在很大差异，但并非以已知的人口统计学和行为差异所预期的方式；来自多伦多的高度入侵性单巢群体并非多样性最低的，也未表现出任何其他独特的替换模式，这表明与入侵或当前单巢性相关的任何过去瓶颈在RNA水平上已变得模糊不清。我们的研究提出了两个与白蚁社会生物学相关的重要假设。第一，对偏向兵蚁的基因推断出的正选择（dN/dS > 1）可能是间接的，且是通过亲缘选择介导的类型；第二，一些社会性昆虫城市入侵（即“单巢性”）伴随的行为变化可能与入侵瓶颈预期的多样性丧失无关。
