Lower Sarah E, Pring Samuel, Tran Hanh, Martinson Katherine, Deering Susan, Price Mathew A, Vestal Brian, Pask Gregory M, Collins Douglas B, Mitchell Robert F
Department of Biology, Bucknell University, Lewisburg, PA, 17837, USA.
Department of Biology, University of Wisconsin Oshkosh, Oshkosh, WI, 54901, USA.
BMC Genomics. 2025 Jul 14;26(1):651. doi: 10.1186/s12864-025-11758-9.
With their charismatic nighttime flashes, fireflies are a classic organismal system for studying the evolution of visual mating signals. However, across their diversity, fireflies employ a variety of mating strategies that include both chemical and visual signals. While phylogenetic evidence points to a common ancestor that relied on long-range pheromones, behavioral evidence suggests that light-dependent flashing fireflies do not use smell for mating. We tested this hypothesis by investigating the olfactory genetics of the dusk-active, light-using common eastern firefly, Photinus pyralis. In insects, odors are primarily detected by odorant receptor (OR) proteins embedded in the dendritic membranes of olfactory receptor neurons. If pheromones are part of mate signaling in light-using fireflies, then one or more OR genes should be upregulated in the antennae of the searching sex (males). We therefore annotated the complete suite of ORs in the genome of P. pyralis and measured expression of OR genes between the sexes using RNAseq.
We identified 102 ORs in the P. pyralis genome, including the conserved single-copy Orco. Our phylogenetic analysis showed lineage-specific OR diversification in P. pyralis relative to other beetle species. Differential expression analysis of male and female antennae and hind legs revealed that a subset of ORs were upregulated in antennae as compared to legs, suggesting a role in adult olfaction. Notably, PpyrOR6 was one of two genes, and the only OR, that was significantly upregulated between male and female antennae, suggesting a sex-specific role such as mate location.
These findings increase known diversity of insect ORs in an understudied beetle family and suggest that fireflies with flashing adults use multimodal signals during mating.
萤火虫凭借其迷人的夜间闪光，成为研究视觉交配信号进化的经典生物系统。然而，在萤火虫的多样性中，它们采用了多种交配策略，包括化学信号和视觉信号。虽然系统发育证据指向一个依赖远距离信息素的共同祖先，但行为证据表明，依赖光闪烁的萤火虫在交配时不使用嗅觉。我们通过研究黄昏活跃、利用光线的东部常见萤火虫（Photinus pyralis）的嗅觉遗传学来检验这一假设。在昆虫中，气味主要由嵌入嗅觉受体神经元树突膜中的气味受体（OR）蛋白检测。如果信息素是利用光线的萤火虫交配信号的一部分，那么一个或多个OR基因应该在搜索性别的触角（雄性）中上调。因此，我们注释了P. pyralis基因组中的完整OR套件，并使用RNA测序测量了两性之间OR基因的表达。
我们在P. pyralis基因组中鉴定出102个OR，包括保守的单拷贝Orco。我们的系统发育分析表明，相对于其他甲虫物种，P. pyralis中存在谱系特异性的OR多样化。对雄性和雌性触角及后腿的差异表达分析表明，与腿部相比，触角中有一部分OR上调表达，这表明其在成虫嗅觉中发挥作用。值得注意的是，PpyrOR6是在雄性和雌性触角之间显著上调表达的两个基因之一且是唯一的OR基因，这表明其具有性别特异性作用（如寻找配偶）。
这些发现增加了一个研究较少的甲虫科昆虫OR的已知多样性，并表明成虫具有闪光的萤火虫在交配时使用多模态信号。
