Mitchell London C, Moczek Armin P, Nadolski Erica M
Department of Biology, Indiana University, Bloomington, 915 East 3 Street, Bloomington IN 47405, USA.
bioRxiv. 2025 Mar 1:2024.10.10.617608. doi: 10.1101/2024.10.10.617608.
Sex-specific trait expression represents a striking dimension of morphological variation within and across species. The mechanisms instructing sex-specific organ development have been well studied in a small number of insect model systems, suggesting striking conservation in some parts of the somatic sex determination pathway while hinting at possible evolutionary lability in others. However, further resolution of this phenomenon necessitates additional taxon sampling, particularly in groups in which sexual dimorphisms have undergone significant elaboration and diversification. Here, we functionally investigate the somatic sex determination pathway in the gazelle dung beetle , an emerging model system in the study of the development and evolution of sexual dimorphisms. We find that RNA interference (RNAi) targeting caused chromosomal females to develop morphological traits largely indistinguishable from those normally only observed in males, and that is sufficient to induce splicing of the normally male-specific isoform of in chromosomal females, while leaving males unaffected. Further, was found to phenocopy previously described RNAi phenotypes of in female but not male beetles. These findings match predictions derived from models of the sex determination cascade as developed largely through studies in . In contrast, resulted in larval mortality and was not sufficient to affect splicing, whereas RNAi targeting and two putative orthologs of yielded no obvious phenotypic modifications in either males or females, raising the possibility that the function of a subset of sex determination genes may be derived in select Diptera and thus non-representative of their roles in other holometabolous orders. Our results help illuminate how the differential evolutionary lability of the somatic sex determination pathway has contributed to the extraordinary morphological diversification of sex-specific trait expression found in nature.
性别特异性性状表达是物种内部和物种之间形态变异的一个显著维度。在少数昆虫模型系统中，指导性别特异性器官发育的机制已得到充分研究，这表明在体性决定途径的某些部分存在显著的保守性，而在其他部分则暗示可能存在进化上的不稳定性。然而，要进一步解析这一现象，需要增加分类群采样，特别是在性二态性已经历显著细化和多样化的类群中。在这里，我们对瞪羚粪金龟的体性决定途径进行了功能研究，瞪羚粪金龟是性二态性发育和进化研究中一个新兴的模型系统。我们发现，针对[基因名称1]的RNA干扰（RNAi）使染色体雌性个体发育出的形态特征与通常仅在雄性个体中观察到的特征基本无法区分，并且[基因名称2]足以诱导染色体雌性个体中通常为雄性特异性的[基因名称3]同工型的剪接，而对雄性个体没有影响。此外，发现[基因名称4]模拟了先前在雌性而非雄性甲虫中描述的[基因名称5]的RNAi表型。这些发现与主要通过对[研究对象]的研究建立的性决定级联模型的预测相符。相比之下，[基因名称6]导致幼虫死亡，并且不足以影响[基因名称7]的剪接，而针对[基因名称8]及其两个假定的直系同源基因的RNAi在雄性和雌性个体中均未产生明显的表型改变，这增加了一种可能性，即性决定基因子集的功能可能在某些双翅目中是衍生的，因此不能代表它们在其他全变态昆虫目中的作用。我们的结果有助于阐明体性决定途径的差异进化不稳定性如何促成了自然界中发现的性别特异性性状表达的非凡形态多样化。
