Lipid composition and extreme temperature tolerance following exposure to fluctuating temperatures in Orchesella cincta

Ectotherms commonly adjust storage and membrane lipid composition to ambient temperature to counteract detrimental thermal effects on lipid fluidity. The effect of repeated temperature fluctuations on fatty acid composition and thermal tolerance was investigated. We exposed Orchesella cincta to two constant temperatures (5ºC and 20°C), and a continuously fluctuating treatment (5ºC/20ºC every two days). Fatty acid composition differed between constant low and high temperatures. Animals were most cold tolerant in the low temperature treatment, while heat tolerance was highest under high temperature. Under fluctuating temperatures, fatty acid composition changed with temperature initially, but later the fatty acid composition stabilized and closely resembled that found under constant warm temperatures. Consistently, heat tolerance in the fluctuating temperature treatment was comparable to the constant warm treatment. Cold tolerance in the fluctuating temperature treatment was intermediate compared to animals acclimated to constant cold or warmth, despite the fact that fatty acid composition was adjusted to warm conditions. This unexpected finding suggests that in animals acclimated to fluctuating temperatures an additional underlying mechanism is involved in the cold shock response. Other aspects of homeoviscous adaptation may protect animals during extreme cold. This paper forms a next step to fully understand the functioning of ectotherms in more thermally variable environments. 66