Thermal shock in Daphnia: cost of diel vertical migrations or inhabiting thermally-unstable waterbodies?
Mikulski, Andrzej; Grzesiuk, Małgorzata; Rakowska, Agnieszka; Bernatowicz, Piotr; Pijanowska, Joanna
published: Aug 1, 2017
published online: Jul 31, 2017
manuscript accepted: Jul 19, 2017
manuscript received: Oct 28, 2016
ArtNo. ESP141019003004, Price: 29.00 €
Abstract Many planktonic invertebrates avoid illuminated water layers where the risk of visual detection by predators is highest, which explains why they move to deeper lake layers during daylight hours. At night, individuals migrate upward, back to warm layers at the surface, which are rich in food. Animals migrating in thermally-stratified lakes and, thus, crossing the thermal gradient twice a day are exposed to various negative factors, including diel changes in experienced temperature. Thermal stress would also be experienced by animals inhabiting very small water bodies that are subject to rapid heating by the sun during the day and cooling at night, or those inhabiting thermally-polluted lakes. In laboratory experiments, we demonstrate a significant reduction in the growth rate in Daphnia magna originating from various clones exposed to diel temperature fluctuations, such as those experienced during vertical migration. In addition, the levels of heat shock proteins (HSP70) are significantly reduced following a rapid change in temperature. We also find that a slow temperature change, such as that potentially experienced by animals that are either slowly migrating or avoiding intensely heated locations, is less costly for Daphnia than a fast temperature change.