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A specific type of insulin-like peptide regulates the conditional growth of a beetle weapon

Evolutionarily conserved signaling by peptide hormones related to insulin is known to underlie the nutrient-dependent regulation of sexually selected weapon growth in animals, but the molecular mechanisms that couple nutritional state to weapon growth remain largely unknown. Okada et al. show that one specific subtype of insulin-like peptide (ILP) responds to nutrient status and thereby regulates weapon size in the broad-horned flour beetle Gnatocerus cornutus. The researchers found that the G. cornutus genome encodes five ILPs (GcorILP1–5) and two insulin-like receptors (GcorInR1, -2). RNA interference revealed that GcorILP2 specifically regulated weapon size, and was highly and specifically expressed in the fat body in a condition-dependent manner. The two receptors are functionally redundant but GcorInR2 is partially specialized for regulating weapon growth. The image shows the variation of weapon size in G. cornutus. Top right is a female; the others are males with varying sizes of mandibles – small (bottom right), medium (top left) and large (bottom left).

Image Credit: Yasukazu Okada