O’BRIEN, DM; FOGEL, ML; BOGGS, CL: Amino acid metabolism in adult Lepidoptera: from biochemistry to life history evolution.

Adequate nutrition is critical to reproduction in animals. In many species, proteins are the nutrient in lowest supply and highest demand. This is particularly true in nectar feeding insects; e.g. Lepidoptera, in which protein provisioning takes place in the larval lifestage and amino acids are later released and used to provision eggs in the adults. Amino acid metabolism is complex and not well understood. We have been using a relatively new technique to explore amino acid metabolism in 5 species of nectar-feeding lepidoptera, and its relationship with broader patterns of life history. We use gas chromatography interfaced with isotope ratio mass spectrometry (GC/C/IRMS) to evaluate variations in the 13C/12C ratio of individual egg amino acids, and thus infer the dietary source of their carbon skeletons. We find that the carbon skeletons of most non-essential amino acids are synthesized from the adult diet, however, the pattern and extent of amino acid synthesis varies among species (as does reproductive strategy). We also find evidence for extensive nitrogen recycling via trans-amination. However, essential amino acids, the carbon skeletons of which cannot be synthesized de novo, derive exclusively from the larval diet. Thus nitrogen per se does not appear to limit egg manufacture in these insects. Rather, adult reproduction appears to be primarily limited by the unique carbon structures found in essential amino acids, which cannot be synthesized or re-conformed as needed.