Abstract
A collection of forty populations were used to study the phenotypic adaptation of Drosophila melanogaster larvae to urea‐laced food. A long‐term goal of this research is to map genes responsible for these phenotypes. This mapping requires large numbers of populations. Thus, we studied fifteen populations subjected to direct selection for urea tolerance and five controls. In addition, we studied another twenty populations which had not been exposed to urea but were subjected to stress or demographic selection. In this study, we describe the differentiation in these population for six phenotypes: (1) larval feeding rates, (2) larval viability in urea‐laced food, (3) larval development time in urea‐laced food, (4) adult starvation times, (5) adult desiccation times, and (6) larval growth rates. No significant differences were observed for desiccation resistance. The demographically/stress‐selected populations had longer times to starvation than urea‐selected populations. The urea‐adapted populations showed elevated survival and reduced development time in urea‐laced food relative to the control and nonadapted populations. The urea‐adapted populations also showed reduced larval feeding rates relative to controls. We show that there is a strong linear relationship between feeding rates and growth rates at the same larval ages feeding rates were measured. This suggests that feeding rates are correlated with food intake and growth. This relationship between larval feeding rates, food consumption, and efficiency has been postulated to involve important trade‐offs that govern larval evolution in stressful environments. Our results support the idea that energy allocation is a central organizing theme in adaptive evolution.
Highlights
An important focus of evolutionary research has been the elucidation of how phenotypes affect survival and reproduction
Larvae with very high feeding rates are less efficient than slower feeding larvae—that is they require more food to successfully pupate (Joshi & Mueller, 1996; Mueller, 1990). These findings suggested that energy trade-offs may be driving the evolution of feeding rates (Mueller & Barter, 2015)
Populations subject to demographic selection show elevated resistance to starvation relative to populations selected for urea resistance
Summary
An important focus of evolutionary research has been the elucidation of how phenotypes affect survival and reproduction (e.g., see Abrahamson & Weiss, 1997). (b) Another 10 populations were derived from populations selected for late reproduction, five were subjected to desiccation stress and five served as controls under mild starvation stress This collection of 10 populations will be referred to as the stress-selected populations. Service et al (1985) showed that populations selected for reproduction at later ages showed increases in adult starvation resistance, desiccation resistance, and ethanol tolerance. Larvae with very high feeding rates are less efficient than slower feeding larvae—that is they require more food to successfully pupate (Joshi & Mueller, 1996; Mueller, 1990) These findings suggested that energy trade-offs may be driving the evolution of feeding rates (Mueller & Barter, 2015). We tested that prediction by measuring feeding rates and larval growth rates of all forty populations
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