Adaptive contraction of diet breadth affects sexual maturation and specific nutrient consumption in an extreme generalist omnivore.

Animals balance their intake of specific nutrients, but little is known about how they do so when foraging in an environment with toxic resources and whether toxic foods promote adaptations that affect life history traits. In German cockroach (Blattella germanica) populations, glucose aversion has evolved in response to glucose-containing insecticidal baits. We restricted newly eclosed glucose-averse (GA) and wild-type (WT) female cockroaches to nutritionally defined diets varying in protein-to-carbohydrate (P : C) ratio (3 : 1, 1 : 1, or 1 : 3) or gave them free choice of the 3 : 1 and 1 : 3 diets, with either glucose or fructose as the sole carbohydrate source. We measured consumption of each diet over 6 days and then dissected the females to measure the length of basal oocytes in their ovaries. Our results showed significantly lower consumption by GA compared to WT cockroaches when restricted to glucose-containing diets, but also lower fructose intake by GA compared to WT cockroaches when restricted to high fructose diets or given choice of fructose-containing diets. Protein intake was regulated tightly regardless of carbohydrate intake, except by GA cockroaches restricted to glucose-containing diets. Oocyte growth was completely suppressed in GA females restricted to glucose-containing diets, but also significantly slower in GA than in WT females restricted to fructose-containing diets. Our findings suggest that GA cockroaches have adapted to reduced diet breadth through endocrine adjustments which reduce requirements for energetic fuels. Our study illustrates how an evolutionary change in the chemosensory system may affect the evolution of other traits that govern animal life histories.