The Effects of Diet on the Expression of Male Dimorphic Colouration and Weaponry in a Species of Neotropical Katydid

Male alternative reproductive tactics are taxonomically widespread, with many species showing males with distinctly different phenotypic characters such as body size or weaponry. Several mechanisms can drive the expression of these male morphs, including genetic polymorphism or environmental interactions during development. In insects, multiple male morphs are common in several orders, including Coleoptera, Odonata, and Hymenoptera, but are rare in Orthoptera. This study establishes the presence of two male phenotypic morphs in the bush cricket <i>Satizabalus jorgevargasi</i>, a species in which the males display mandibular weaponry, and tests the effects of diet on the expression of male dimorphic characters. Male nymphs were raised under standard conditions until adulthood, whereupon morphological measurements were taken. Males raised under standard conditions showed two male phenotypes on the basis of head size and body colouration-a major morph with larger heads and more colouration, and a smaller and duller minor morph. A second group of male nymphs were housed individually and fed either a high-protein diet or a high-carbohydrate diet. Body weight and pronotum length were measured on a weekly basis as the nymphs developed, and once the males had matured, morphological and bioacoustic characters were measured. Diet had a significant impact on these male dimorphic characters, with protein-fed males having significantly larger heads and mandibles. Additionally, males reared on the high-protein diet had significantly more regions with colour when compared to carbohydrate-fed males. Our data parallel that seen in other invertebrate groups, where higher levels of protein during maturation are key to the production of larger male morphs.