Rules of nutrient allocation to storage: A critical component of insect life histories

Abstract

Nutrient storage is an important, but understudied life history trait. One approach to characterizing the role of nutrient storage in insect life histories begins with determining the rules that organisms use to allocate nutrients to storage in comparison to other life history traits. My dissertation research focuses on understanding rules of allocation to nutrient storage in two types of insects that differ in their life histories, grasshoppers and ants. First, I showed that the grasshopper, Schistocerca americana , differs from other known grasshoppers by having only a single dominant storage hexamerin that occurs in both larvae and adults. Second, I showed that allocation between somatic growth and lipid storage at the last larval-adult molt in females of the grasshopper, Schistocerca americana, was plastic in response to larval resource availability. On the best growth diet, individuals were larger and contained proportionally greater lipid stores than individuals on the lowest nutrient content diet. Prioritization of nutrient allocation to somatic growth over lipid storage on poor diets in Schistocerca americana females suggests that larvally derived lipid stores have some role in adult fitness, but that body size is more important. Third, I showed that two closely related members of the Camponotus festinatus species complex of desert carpenter ants differ in their life histories with respect to lipid storage. Dark-form workers and soldiers stored significantly more lipid per unit lean mass than light-form workers or soldiers, but light-form colonies involved a slightly larger proportion of soldiers in storing lipid. Fourth, we showed that there was a relationship between storage protein content of queens and founding strategies in five species of Harvester Ants in the genus Pogonomyrmex. Independent claustral-founding species contained the greatest protein stores, followed by independent facultative-foraging queens. Independent obligate-foraging queens, and queens of a dependent social parasite contained almost no protein stores. Last, we showed that arboreal and terrestrial ants differed in both seasonal foraging activity and nutritional preferences in a lowland neo-tropical forest. Differences in foraging and nutritional preferences likely reflect fundamental differences in nutrient availability in the two habitats.