Life-extending dietary restriction and ovariectomy result in similar feeding rates but different physiologic responses in grasshoppers

Abstract

Dietary restriction (DR) and reduced reproduction each extend life span in many species. Females undergoing DR typically experience a reduction in their fecundity, which raises the question of whether the two treatments are actually extending life span in overlapping ways. Life span in lubber grasshoppers has been shown to be increased by DR, and separately by ovariectomy (OVX). Here, we test the combination of these on life span. If life extension by the two treatments are additive, it would suggest that they likely act through separate pathways. The experimental groups were: fully reproductive and fully fed (ShamFD); ovariectomized and fully fed (OVX FD); fully reproductive and restricted diet (ShamDR); and ovariectomized and restricted diet (OVX DR). The median life spans of these groups were: ShamFD = 245 d, OVX FD = 285 d, ShamDR = 286 d, and OVX DR = 322 d. Feeding rate for the OVX FD group was 64% of ad libitum, not significantly different from the 70% of ad libitum that was used for ShamDR. We also measured hemolymph parameters of physiology in these same individuals. Hemolymph levels of vitellogenin (the egg yolk-precursor protein) were increased 5-fold by OVX, but were not affected by DR. In addition, hemolymph total anti-oxidant activity (per μg protein) was significantly reduced by OVX, but was not affected by DR. We show that OVX and DR produce different physiological responses in grasshoppers, despite life extensions and feeding levels that were not significantly different. These data suggest that OVX and DR might extend life span via distinct pathways.

Vitellogenin-RNAi and ovariectomy each increase lifespan, increase protein storage, and decrease feeding, but are not additive in grasshoppers

“…As in previous studies (e.g., Drewry et al 2011), body masses for all treatments increased rapidly until about 3 weeks, and continued to increase slowly until a median age of 6 weeks, a time just following the oviposition of the first clutch in fully reproductive individuals (Fig. 3).…”

“…Animals with both ovariectomy and VgRNAi treatment maintained the same feeding levels as the other reduced reproduction groups, indicating that the changes to feeding were not additive. Drewry et al (2011) show that ovariectomy reduces feeding (~40%) and proposed that other ways to reduce reproduction may also decrease feeding as well.…”

“…For example, each treatment must be complete in its own right (e.g., the ovary completely removed, not partially removed) to test whether another treatment can add to it. The vast majority of studies that have combined two means of reducing reproduction in concert have included dietary restriction as one of the means (e.g., Mair et al 2004; Drewry et al 2011). Dietary restriction typically both extends lifespan (Nakagawa et al 2011) and reduces reproduction (e.g., Tatar 2011; see Lee et al 2014 for an exception).…”

“…These animals have easily determined feeding rates, are amenable to surgery, and are large enough to allow serial sampling of hemolymph. We can directly reduce reproduction by ovariectomy (Hatle et al 2003), which increases lifespan by ~20% and reduces feeding by ~50% (Hatle et al 2008; Drewry et al 2011). Ovariectomy has been shown to double fat body mass and hemolymph volume (Hatle et al 2013).…”

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

“…We have previously shown that ovariectomized grasshoppers have ~20% greater median life span than sham-operated controls (Hatle et al 2008; Drewry et al 2011). In contrast to other models in which the ovary is missing, ovariectomized grasshoppers continue to make the egg yolk-precursor protein vitellogenin, which accumulates in the hemolymph (Hatle et al 2003).…”