Insulin signaling’s role in mediating tissue-specific nutritional plasticity and robustness in the horn-polyphenic beetle Onthophagus taurus

Organisms cope with nutritional variation via developmental plasticity, adjusting trait size to nutrient availability for some traits while enabling others to develop in a nutritionally robust manner. Yet, the developmental mechanisms that regulate organ-specific growth across nutritional gradients remain poorly understood. We assessed the functions of members of the insulin/insulin-like signaling pathway (IIS) in the regulation of nutrition sensitivity and robustness in males of the horn-polyphenic beetle Onthophagus taurus, as well as potential regulatory interactions between IIS and two other growth-regulating pathways: Doublesex and Hedgehog signaling. Using RNA interference (RNAi) we experimentally knocked down both insulin receptors (InR1, InR2) and Foxo, a growth inhibitor. We then performed morphometric measurements on horns, a highly nutrition-sensitive trait, and genitalia, a largely nutrition-insensitive trait. Finally, we used qRT-PCR to assess expression levels of Doublesex...