Ovariectomy in grasshoppers increases somatic storage, but proportional allocation of ingested nutrients to somatic tissues is unchanged

Abstract

Reduced reproduction increases storage and extends lifespan in several animal species. The disposable soma hypothesis suggests this life extension occurs by shifting allocation of ingested nutrients from reproduction to the soma. A great deal of circumstantial evidence supports this hypothesis, but no direct tracking of nutrients has been performed in animals that are long-lived because of direct reduction in reproduction. Here, we use the stable isotopes to track carbon and nitrogen from ingestion to somatic organs in long-lived, ovariectomized grasshoppers. Three estimates of somatic storage (viz., quantity of hemolymph storage proteins, amount of femur muscle carbohydrates, and size of the fat body) all doubled upon ovariectomy. In stark contrast, ovariectomy did not increase the proportion of these tissues that were made from recently ingested foods. In other words, the physiology underlying relative allocation to these somatic tissues was not affected by ovariectomy. Thus, at the level of whole tissue storage, these results are consistent with a trade-off between reproduction and longevity. In contrast, our stable isotope data are inconsistent with the prediction that enhanced storage in ovariectomized females results from a physiological shift in allocation of ingested nutrients.