Flies evolved small bodies and cells at high or fluctuating temperatures.

Recent theory predicts that the sizes of cells will evolve according to fluctuations in body temperature. Smaller cells speed metabolism during periods of warming but require more energy to maintain and repair. To evaluate this theory, we studied the evolution of cell size in populations of held at either a constant temperature (16°C or 25°C) or fluctuating temperatures (16 and 25°C).

Indirect selection of thermal tolerance during experimental evolution of Drosophila melanogaster.

Natural selection alters the distribution of a trait in a population and indirectly alters the distribution of genetically correlated traits. Long-standing models of thermal adaptation assume that trade-offs exist between fitness at different temperatures; however, experimental evolution often fails to reveal such trade-offs. Here, we show that adaptation to benign temperatures in experimental populations of Drosophila melanogaster resulted in correlated responses at the boundaries of the thermal niche.

Heat tolerance during embryonic development has not diverged among populations of a widespread species (Sceloporus undulatus).

The frequency and magnitude of heat waves have increased in recent decades, imposing additional stresses on organisms in extreme environments. Most reptilian embryos are regularly exposed to thermal stress because they develop in shallow, warm soils for weeks to months. We studied cardiac performance during warming to infer lethal temperatures for embryonic lizards in the Sceloporus undulatus complex.