Cross-stage consequences of egg temperature in the insect Manduca sexta

Abstract

Summary 1. An organism’s environment, particularly early in development, can profoundly shape its future phenotypes. While the long-term consequences of embryonic temperature are well studied in vertebrates, insects have complex life cycles that may uncouple temperature’s effects in one stage from physiology in the next. 2. This study examines how egg temperature affects insect performance across all subsequent life stages. We focused on the hawkmoth, Manduca sexta, and examined how egg temperatures affected hatching time, hatchling mass, larval growth, development time, head capsule size, pupal mass and adult fecundity. Eggs were exposed to either diurnal temperature cycles or a single heat shock; in both experiments, temperatures were within the range to which eggs are typically exposed in the field. 3. Although the consequences of egg temperature varied depending on the type of treatment, both cycling temperatures and heat shock affected egg development time and initial larval growth rate, which likely have fitness consequences for M. sexta in nature. In contrast, egg temperature had no persistent effect on any trait measured in later larval stages, pupae or adults. 4. Organisms with complex life cycles –Manduca has four distinct life stages and multiple larval sub-stages – may benefit from rapid compensation for poor early conditions. Additionally, the modularity of insect life cycles may help insects cope with environmental variability by insulating later stages from disturbances during embryogenesis.