Diet influences resting metabolism in adult, female Gryllus firmus crickets

An organism’s feeding decisions have consequences for physiological function, yet links between feeding, metabolic physiology and organismal life-history traits are rarely explored.  We examined the effects of variation in dietary protein and carbohydrate availability on the resting metabolic rates of female Gryllus firmus crickets from populations selected to produce either flight-capable [long-winged; LW(f)] or flightless (short-winged; SW) adults.  In this species, flight ability trades-off with early fecundity; short-winged crickets begin reproducing sooner than their long-winged counterparts.  We gave adult crickets (n=130) one of 13 diets with different relative and absolute amounts of protein and carbohydrate, and allowed them to feed for five days, before measuring resting metabolism via indirect calorimetry (carbon dioxide production).  Feeding patterns differed between the morphs, with LW(f) crickets consuming more food when given carbohydrate-biased diets, and SW crickets eating more on protein-biased diets.  Despite feeding differences, cricket mass gain patterns were similar between morphs, with higher mass gain on high-macronutrient diets.  Mass-independent resting metabolic rates were also similar between morphs, and higher among crickets given foods with higher total macronutrient contents.  This indicates a direct connection between food quality and resting metabolism, but without a clear link to life-history evolution.