Flies developed smaller cells when temperature fluctuated more frequently

• Flies developed under frequent or infrequent fluctuations between two temperatures.
• In both treatments, flies experienced the same total exposure to each temperature.
• Frequent fluctuations caused flies to build smaller epidermal cells for a given body size.
• Tissues made of small cells have more nuclei and larger area of plasma membranes.
• The reduction in cell size could enhance metabolic performance during warming.

Changes in cell size might be an important component of adaptation to thermal heterogeneity. Although Drosophila melanogaster develops smaller cells at fluctuating temperatures, we do not know whether this response depends on the frequency or amplitude of thermal change. In a laboratory experiment, we exposed flies to either frequent or infrequent fluctuations between 17 and 27 °C, while controlling the total exposure to each temperature. Flies emerged from these treatments with similar body sizes, but flies at more frequent fluctuations emerged earlier and had smaller epidermal cells for a given body size. Tissue built from small cells has more nuclei for transcription, shorter distances between cell compartments, and a larger surface area for transport across membranes. Therefore, we hypothesize that physiological effects of small cells reduce lags in metabolic activity and enhance performance of flies during warming. For plasticity of cell size to confer a fitness advantage, this hypothetical benefit must outweigh the cost of maintaining a greater area of plasma membrane.

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