WASKEY, TJ; HATLE, JD; JULIANO, SA; Illinois State Univ: Vitellogenin production rates underlying reproductive plasticity and canalization in the lubber grasshopper

The study of physiology underlying phenotypic plasticity of reproduction seeks to explain how organisms developmentally alter reproductive tactics in response to environmental perturbations. We measured ovarian masses, oocyte lengths, and rates of egg-yolk protein (vitellogenin) production in the lubber grasshopper (Romalea microptera). Previous work suggests that lubber egg production is initially plastic but then becomes unresponsive (canalized) to changes in food availability; age at reproduction becomes canalized early, and later, number of eggs becomes canalized. Grasshoppers fed a 5% protein diet (5%) had significantly (P<0.05) heavier ovaries at ages 11, 22, and 33 d, longer oocytes at ages 22 and 33 d, and greater Vg production at age 22 d, than did grasshoppers of the same ages fed a 1% protein diet (1%). Vitellogenin (Vg) production peaked significantly at age 22 d in 5% grasshoppers and tended to peak at age 33 d in 1% grasshoppers. Other grasshoppers were fed diet regimes that included abrupt switches in protein content, enabling us to test for canalization of reproductive traits. Neither increasing nor decreasing dietary protein at age 25 d affected ovarian mass, oocyte length, or Vg production (P > 0.05), all tested at age 33 d. In contrast, reducing dietary protein at age 14 d significantly reduced Vg production, oocyte length, and ovarian mass (P< 0.05), all tested at age 22 d. Hence, ovarian development, oocyte development, and the rate of Vg production appear to become unresponsive to feeding between ages 14 and 25 d (40% to 70% of the duration of the first oviposition cycle). These results are consistent with the hypothesis that Vg production is a key component of the canalized phase of reproductive development. Supported by NSF IBN9978810 to SAJ.