From energy efficiency under stress to rapid development and a long life in natural populations.

Simplistically, high fitness depends upon high energy efficiency in the stressful habitats of organisms in the wild. Rapid development and high survival to adulthood should be followed by long-lived stress-resistant genotypes under this reductionist model. Empirical evidence is very limited because of the common use of benign laboratory environments, which remains a major difficulty in understanding relationships between life-history traits under more natural settings. Heterozygotes tend to show greater energy efficiency than do corresponding homozygotes especially in stressful environments, which leads the above connections among fitness traits. In particular rapid development and increased longevity should be correlated, and underwritten by the availability of metabolic energy. Empirical work is needed based upon severe stresses where a small environmental perturbation cases lethality; drought, heat and nutritional inadequacy are suitable candidate stresses. The importance of viewing fitness in energy terms is emphasized throughout. A byproduct is the potential to fuse functional and evolutionary biology under stressful environments.