Developmental plasticity of thermal performance curve for reproduction in Drosophila melanogaster

In ectotherms, body temperature is a crucial determinant of performance and fitness, as captured by thermal performance curves (TPCs). Since survival in variable environments is often facilitated by phenotypic plasticity, to reliably assess an organism's ability to cope with thermal changes, it is necessary to characterize not only TPCs but also their reaction norms. While previous studies have investigated plasticity in TPCs, these studies focus only on selected parameters and a few developmental temperatures. They may, therefore, overlook the complexity of developmental plasticity in TPCs. Here, we examined the full extent of thermal developmental plasticity in TPCs for fecundity and hatchability in Drosophila melanogaster. By employing a factorial design with ten developmental and twelve adult temperatures, our study enabled a comprehensive characterization of reaction norms of all key TPC parameters. We found that developmental temperature had a significant impact on the egg production rate, with minor effects on other TPC parameters. Nonoptimal developmental temperatures negatively affected most TPC parameters, whereas development at 22-26 °C maximized reproductive fitness. We also revealed that developmental plasticity for the maximum reproductive performance might be predominantly caused by developmentally-induced changes in ovariole number. Our results in conjunction with previous studies on intraspecific variation suggest that any changes in TPC for reproduction primarily involve the egg production rate, indicating that adaptive evolution and phenotypic plasticity followed the same pathway. Overall, our findings underscore the limitations of developmental plasticity in enhancing reproductive fitness, suggesting that while certain traits, such as egg production rate, may be relatively plastic, these changes may not be sufficient to enable effective adjustment to environmental shifts.