How do nutritional intake targets and requirements change during development of a generalist invertebrate herbivore?

Abstract

Matching nutritional requirements throughout development is critical for maximizing adult performance and fitness. Mammalian maternal milk is the ultimate example of a diet well-matched to meet all requirements of developing infants. Its macronutrient content, specifically, protein:non-protein (p:np) ratio, changes to match shifting requirements during infant development. Indeed, the developmental requirements of humans, rodents and livestock are well-described, during juvenile development. However, despite their importance as research models and in ecosystems, the dynamics of nutritional requirements in developing invertebrates is still poorly understood. Here we studied the nutritional requirements and performance from hatching to adulthood of a generalist herbivore, the South American locust, Schistocerca cancellata. In order to do so, we measured protein and carbohydrate consumption from two artificial diets differing strongly in protein:carbohydrate content for the six juvenile instars and adults of the S. cancellata. In addition, we measured growth and survival of locusts reared on single artificial diets varying in protein:carbohydrate ratio for their entire developmental period. When given a choice, demand for protein decreased throughout development, demonstrated by a change in self-selected intake targets from protein-biased in early life, to highly carbohydrate-biased in young adults. Probably because early instars must prioritize growth, while the last instar and adults must prioritize preparation for dispersal and reproduction. On no-choice diets, lifetime animal performance, including developmental rate and mass gain, was highest on protein-biased foods, especially during early development. Regardless of late-juvenile diet, if individuals were not able to obtain sufficient protein in the early juvenile period, they were unable to catch up in size or developmental speed.