HATLE, J.D.*; BORST, D.W.; ESKEW, M.R.; JULIANO, S.A.: Maximum titers of vitellogenin and storage protein occur during the canalized phase of grasshopper oogensis
Many organisms meet the challenge of unpredictable environmental conditions by remaining developmentally flexible early in their development and only later enter a canalized (inflexible) phase of development. Our ultimate goal is to understand the physiological mechanisms that underlie this strategy in a clutch-laying grasshopper (Romalea microptera). We examined the relationships of protein titers and the transition from flexible to inflexible reproduction. Titers of both storage proteins (SPs) and vitellogenin (VG, a precursor of yolk protein) are low in the first half of the oviposition cycle and increase to maxima in the second half of the cycle. To produce defined canalized phases, we raised hoppers on four diets that varied in their quantity of food: 1) high; 2) high switched to low; 3) low switched to high; 4) low. Serial hemolymph samples were collected every 4 days until oviposition, and the maximum levels of VG (VGmax) and SPs (SPmax) for each individual (and age at which they occurred) were determined. We observed no effect on VGmax levels, but SPmax levels in hoppers fed diets 3 and 4 were half that of hoppers fed diets 1 and 2. The time from eclosion to VGmax was significantly greater in hoppers fed diets 3 and 4, whereas the time from VGmax to oviposition was not. Similarly, time from eclosion to SPmax was significantly greater in hoppers fed diets 3 and 4, whereas the time from SPmax to oviposition was not. These data show that VGmax and SPmax are physiological landmarks associated with the canalized phase of oogenesis in grasshoppers. We hypothesize that factors that inhibit the increase of VG and SP titers may be involved in the initiation of canalization. (Supported by NSF grant DB1-9978810 to DB & SJ.)
