Organisms must allocate resources to either somatic storage
or reproduction, yet the physiological mechanisms coordinating this trade-off
are poorly understood. In the lubber grasshopper, vitellogenin (Vg) is the precursor protein to vitellin, which
constitutes 90% of protein in mature oocytes. Previously, to investigate how
investment into somatic storage is affected by reproductive protein resources,
we utilized RNA interference (RNAi), reducing Vg-mRNA in the fat body 30-fold,
however Vg protein in the hemolymph increased.
Additionally, Vg-RNAi treatment halted ovarian growth and doubled fat
body mass. In this study, we measured hemolymph levels of 90 kDa hexameric
storage protein (Hex90), ovarian vitellin content, and rates of Vg production
by the fat body. We compared Vg-RNAi treated individuals to Hex90-RNAi or
buffer-injected controls by injecting dsRNA before vitellogenesis and sampling
from early to late vitellogenesis. Hex90-RNAi treatment reduced Hex90 levels
when compared to the buffer-injected and Vg-RNAi groups combined (P=0.04). The
Vg-RNAi group had significantly lower vitellin content per gram of ovary
compared to buffer-injected (P=0.006), but not the Hex90-RNAi (P=0.360) group,
indicating that Vg-RNAi treatment may prevent Vg from being sequestered into
developing oocytes. In addition, rate of Vg production by the fat body was
higher at 19 d than at 26 d (P=0.002) but was not affected by Vg-RNAi
treatment (P=0.383). Together, these results suggest that Vg-RNAi treatment
does not reduce the translation rate of Vg-mRNA, but nonetheless halts sequestration
of Vg into developing oocytes and increases fat body mass, consistent with a trade-off
between reproduction and storage.
