How dietary protein and carbohydrate influence field cricket development, size and mate attraction signalling

Researchers examining how nutrition impacts fitness traits usually examine one nutrient at a time, ignoring potential interactions. When researchers simultaneously examine multiple nutrients, their studies often focus on adults, ignoring potential changes in nutritional needs that occur during the transition between juvenile and adult stages. To address these issues, we quantified how dietary nutrient balance (relative amounts of protein and carbohydrate) during development and into adulthood influenced life history and sexually selected traits using male Jamaican field crickets, Gryllus assimilis. Our findings revealed that male crickets developed significantly faster and grew larger when they were reared on a protein-rich diet, but their average daily time spent signalling for mates was significantly higher when they were reared on a carbohydrate-rich diet. Furthermore, while the probability of signalling and daily time spent signalling increased with age, time spent signalling for mates tended to increase at a higher rate with age when males consumed a carbohydrate-rich diet in adulthood. Together our findings suggest that traits may differ in their nutrient requirements, resulting in diet influencing a possible trade-off between traits across different life stages. The ability to locate and consume foods rich in protein during development should impact adult male fitness, as protein availability results in larger males, and larger males typically produce more attractive signals and are preferred by females. Conversely, the ability to locate and consume foods rich in carbohydrate should also impact a male's fitness, as males signal with higher effort when fed carbohydrate-rich diets, and higher signalling effort can directly impact a male's ability to attract a female.