Plasticity of grasshopper vitellogenin production in response to diet is primarily a result of changes in fat body mass

Abstract

Life history plasticity is the developmental production of different phenotypes by similar genotypes in response to different environments. Plasticity is common in early post-embryonic or adult development. Later in the developmental stage, the transition from developmentally plastic to canalized (i.e., inflexible) phases is often associated with the attainment of a threshold level of storage. Thresholds are often described simply as total body mass or cumulative consumption of food. The physiological characteristics of thresholds, such as the contributions of the growth of particular organs or the production rate of proteins, are largely unstudied. To address the physiology underlying a threshold-induced developmental transition, total vitellogenin production in response to diet quality in the lubber grasshopper was studied. For individuals that differed in age or dietary protein, somatic mass, ovarian mass, fat body mass, mass-specific vitellogenin production, vitellogenin titer, and storage protein titer were measured. Age and diet strongly affected these parameters, with ovarian mass and fat body mass contributing most to the differences. During mid vitellogenesis, females were highly plastic in response to changing food quality. Only during late vitellogenesis were females unresponsive to changes in food quality. Fat body mass was a more important component of plasticity than was mass-specific vitellogenin production. Because these two variables together make up total vitellogenin production, the greater contribution of fat body mass than mass-specific vitellogenin production suggests that growth factors may be more important than tissue stimulators in producing developmental changes in total vitellogenin production. To our knowledge, this is the first study to demonstrate that mass gain of an organ is more important to developmental plasticity than is the output of that same organ.

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

“…More severe food limitation in this grasshopper (30 -40% of ad libitum) reduced hemolymph protein levels by 40%, without halting reproduction; this result was highly statistically significant and was repeatable across two experiments (Hatle et al 2001;. That life-extending CR did not alter protein storage is particularly surprising for a phytophagous insect, because they are protein limited during major life history transitions (e.g., Hatle et al 2003a;Hatle et al 2006). Hence, the present results do not support the hypothesis that protein storage is involved in life extension by CR.…”

“…These CR diets significantly increased longevity but did not alter tactics of the first clutch. This interesting result calls for further studies to determine if these patterns of longevity and reproductive output hold in the wild, and whether other storage parameters, such as fat body mass (shown to be most important in reproductive plasticity by Hatle et al 2006), are affected by these diets.…”

“…For example, hemolymph levels of gonadotropic hormones (i.e., juvenile hormone) and vitellogenin vary 10-fold across individuals of the same age, but the shape of the developmental profiles of these factors is consistent across individuals (cf. Hatle et al 2000;2003a,b;to Hatle et al 2006). …”

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

“…These results suggest that JH may not be the only factor involved in the regulation of vitellogenin production, but instead some other nutrition-dependent change is needed. Similarly, Hatle et al found that total vitellogenin production relies more on total fat body mass than on massspecific tissue stimulation (typically by JH) (Hatle et al, 2006a). This suggests that growth factors affecting the fat body, which are likely nutrition dependent, might be a co-requirement with JH for vitellogenesis (Hatle et al, 2006a).…”

“…Similarly, Hatle et al found that total vitellogenin production relies more on total fat body mass than on massspecific tissue stimulation (typically by JH) (Hatle et al, 2006a). This suggests that growth factors affecting the fat body, which are likely nutrition dependent, might be a co-requirement with JH for vitellogenesis (Hatle et al, 2006a). Hence, studies on vitellogenin production suggest threshold feeding is needed both to initiate production of JH and to bring about competence to JH.…”