Renewable and nonrenewable resources: Amino acid turnover and allocation to reproduction in Lepidoptera

TLDR

The allocation of nutritional resources to reproduction in animals is complex, with egg nutrients divided into renewable resources synthesized from adult dietary sugars and nonrenewable resources derived exclusively from larval diet. The study aims to determine whether essential and nonessential egg amino acids correspond to nonrenewable and renewable nutrient classes by using compound‑specific stable isotope analysis of carbon in a nectar‑feeding hawkmoth. The authors employed compound‑specific stable isotope analysis of carbon (GC/combustion/isotope ratio MS) on egg amino acids from females raised on isotopically distinct larval and adult diets to trace nutrient origins. Essential egg amino acids are derived solely from the larval diet, whereas nonessential amino acids are increasingly synthesized from adult nectar sugars, showing that female Lepidoptera can produce a large fraction of egg amino acids from nectar sugars but that essential amino acids limit the potential of adult dietary resources to boost reproduction.

Abstract

The allocation of nutritional resources to reproduction in animals is a complex process of great evolutionary significance. We use compound-specific stable isotope analysis of carbon (GC/combustion/isotope ratio MS) to investigate the dietary sources of egg amino acids in a nectar-feeding hawkmoth. Previous work suggests that the nutrients used in egg manufacture fall into two classes: those that are increasingly synthesized from adult dietary sugar over a female's lifetime (renewable resources), and those that remain exclusively larval in origin (nonrenewable resources). We predict that nonessential and essential amino acids correspond to these nutrient classes and test this prediction by analyzing egg amino acids from females fed isotopically distinct diets as larvae and as adults. The results demonstrate that essential egg amino acids originate entirely from the larval diet. In contrast, nonessential egg amino acids were increasingly synthesized from adult dietary sugars, following a turnover pattern across a female's lifetime. This study demonstrates that female Lepidoptera can synthesize a large fraction of egg amino acids from nectar sugars, using endogenous sources of nitrogen. However, essential amino acids derive only from the larval diet, placing an upper limit on the use of adult dietary resources to enhance reproductive success.