Natural variation in plasticity of glucose homeostasis and food intake.

Balancing the acquisition, allocation and storage of energy during periods of food deprivation is critical for survival. We show that natural variation in the foraging (for) gene, which encodes a cGMP-dependent protein kinase (PKG) in the fruit fly Drosophila melanogaster, affects behavioral and physiological responses to short-term food deprivation. Rover and sitter, natural allelic variants of for, differ in their stored carbohydrate reserves as well as their response to short-term deprivation. Fewer carbohydrates are stored in the fat body of rovers compared with sitters, and more labeled glucose is allocated to lipid stores compared with carbohydrate stores during a short feeding bout. Short-term food deprivation decreases hemolymph glucose levels in rovers but not in sitters. After food deprivation, rovers increase their food intake more slowly than sitters, and rover hemolymph levels take longer to respond to re-feeding. Finally, rovers have lower adipokinetic hormone (akh) mRNA levels than sitters. Our data suggest that for mediates larval responses to short-term food deprivation by altering food intake and blood glucose levels.

Natural variation in food acquisition mediated via a Drosophila cGMP-dependent protein kinase.

In natural environments where food abundance and quality can change drastically over time, animals must continuously alter their food acquisition strategies. Although genetic variation contributes to this plasticity, the specific genes involved and their interactions with the environment are poorly understood. Here we report that natural variation in the Drosophila gene, foraging (for), which encodes a cGMP-dependent protein kinase (PKG), affects larval food acquisition in an environmentally dependent fashion. When food is plentiful, the wild-type rover (for(R)) allele confers lower food intake and higher glucose absorption than both the wild-type sitter (for(s)) allele and the mutant for(s2) allele. When food is scarce, for(R), for(s) and for(s2) larvae increase food intake to a common maximal level, but for(R) larvae retain their increased absorption efficiency. Changes in for expression can induce corrective behavioral modifications in response to food deprivation. When reared in environments with low food levels, for(R) larvae have higher survivorship and faster development than for(s) and for(s2) larvae. Together, these results show that natural variation in for has far reaching implications affecting a suite of phenotypes involved in the regulation of food acquisition.