Hemolymph ecdysteroids do not affect vitellogenesis in the lubber grasshopper

Abstract

The role of hemolymph ecdysteroids in the reproduction of non-dipteran insects is unclear. We examine the role(s) of hemolymph ecdysteroids during egg production in the lubber grasshopper, Romalea microptera. In all individuals, hemolymph ecdysteroids rose to a sharp peak with similar maxima and then fell to undetectable levels. The time from the adult molt to the maximum ecdysteroid titer (E(max) titer) varied in response to food availability, whereas the time from E(max) titer to oviposition was unrelated to food availability. Because both the timing of egg production and the timing of E(max) responded similarly to environmental changes, ecdysteroids may be involved in egg production. We hypothesized that this role is the stimulation of vitellogenesis. Ovariectomized females had vitellogenin but no ecdysteroids, so ecdysteroids are not necessary for vitellogenin production. In addition, treatment of females with ecdysteroids altered neither Vg titers nor ovarian growth. Ovarian ecdysteriods increased at the same age in development as hemolymph ecdysteroids. In contrast to hemolymph ecdysteroids, ovarian ecdysteroids persisted until oviposition. Despite this, [(3)H]ecdysone injected into the hemolymph was detected later only at very low levels in the ovary, suggesting that hemolymph ecdysteroids are not sequestered by the ovary. In summary, our studies indicate that hemolymph ecdysteroids in adult females of the lubber grasshopper are associated with the timing of egg production, but they neither regulate vitellogenesis nor act as a source of ecdysteroids for the ovary.

Regulation of Drosophila circadian rhythms by miRNA let-7 is mediated by a regulatory cycle

“…To determine the titre of 20E in the heads, we performed a radioimmunoassay developed by David Borst 61 . Briefly, samples were extracted from 50 adult heads by homogenization in 90% methanol.…”

Calorie restriction and late-onset calorie restriction extend lifespan but do not alter protein storage in female grasshoppers

“…On severe CR (~30%), the peak level of hemolymph protein is reduced by ~40%, and the peak is greatly delayed (Hatle et al 2001;. Peak titers of the major gonadotropins, juvenile hormone and ecdysteroids (Hatle et al 2000;2003b), and the egg-yolk precursor protein vitellogenin (Hatle et al 2001), are similarly delayed.…”

A cumulative feeding threshold required for vitellogenesis can be obviated with juvenile hormone treatment in lubber grasshoppers

“…Despite these large differences in cumulative consumption, when JH was controlled, the only variable affected by diet was the number of secondary oocytes. Previous work has repeatedly found strong effects of diet on the timing of first oviposition, age at Vg maximum and the number of eggs (Moehrlin and Juliano, 1998;Hatle et al, 2000;Hatle et al, 2001;Hatle et al, 2003a;Hatle et al, 2003b;Hatle et al, 2004;Juliano et al, 2004). By controlling JH levels, the present paper suggests that feeding for vitellogenesis is required only to produce adequate JH.…”

“…During the oviposition cycle, JH levels start at zero, first rise to low levels (which corresponds to the initiation of vitellogenin production), then rise to a maximum around mid-vitellogenesis (which corresponds to oocyte growth and patency) and finally fall before oviposition. The maximum titer of JH is the point at which JH degradation becomes favored over JH synthesis; the maximum always occurs about 12·days before oviposition Hatle et al, 2003a). These studies on the effects of nutrition on JH levels suggest that threshold feeding (see Juliano et al, 2004) (Fig.·1) is only needed to allow production of JH, and the female is competent to respond to JH prior to attaining the threshold.…”

“…By contrast, in low-fed animals (0.12·g dry mass·day -1 ), first oviposition occurs ~65·days after the adult molt Hatle et al, 2003a). Mature females generally lay 2-3 clutches during their life (Hatle et al, 2006b).…”