Effects of temperature and dietary sterol availability on growth and cholesterol allocation of the aquatic keystone speciesDaphnia

Abstract

SUMMARYEnhanced water temperatures promote the occurrence of cyanobacterial blooms, which may be detrimental to aquatic herbivores. Especially, the often-dominant crustaceans could be negatively affected because cyanobacteria are deficient in phytosterols, which are required by the crustaceans to form the membrane component cholesterol, which in turn plays a role in thermal adaptation. Here, we determined the influence of temperature on growth, reproduction and the allocation of dietary sterol into somatic tissues and eggs of the keystone species Daphnia magna raised along a dietary cholesterol gradient. Mass-specific growth rates of D. magna increased with the increasing availability of dietary cholesterol up to an incipient limiting level, which increased with increasing temperature. This indicates a higher demand for cholesterol for growth at higher temperatures and may explain the consistently smaller clutch sizes of reproducing females at the highest temperature. The cholesterol content of the individuals increased with increasing dietary cholesterol; this increase was enhanced at higher temperatures, indicating a higher demand for cholesterol for tissues and probably specifically for membranes. Surprisingly, the daphnids showed different allocation strategies with regard to temperature and dietary sterol availability. The cholesterol content of eggs was enhanced at higher temperature, which suggested that females allocate more cholesterol to their offspring, presumably to ensure sufficient egg development. When dietary cholesterol was limiting, however, females did not allocate more cholesterol to their eggs. Our data suggest that during cyanobacterial blooms, a potential dietary sterol limitation of Daphnia can be intensified at higher water temperatures, which can occur with global warming.

Interaction of changes in food quality and temperature reveals maternal effects on fitness parameters of a keystone aquatic herbivore

“…So far, no study combined the effects of food quality and temperature across generations as we have done in our experiment. Sperfeld and Wacker (2009) found a higher demand for cholesterol for growth at higher temperatures. They also found that mothers invested more cholesterol into eggs at higher temperatures but only if dietary cholesterol content was not limiting (Sperfeld and Wacker 2009).…”

“…Sperfeld and Wacker (2009) found a higher demand for cholesterol for growth at higher temperatures. They also found that mothers invested more cholesterol into eggs at higher temperatures but only if dietary cholesterol content was not limiting (Sperfeld and Wacker 2009). Cholesterol content of maternal diet may therefore be expected to affect offspring quality more strongly at higher temperatures.…”

“…The interaction between effects of food quantity and temperature has been studied extensively in Daphnia (Orcutt and Porter 1984;Giebelhausen and Lampert 2001), especially in relation to temperature and food gradients in stratified lakes (Stich and Lampert 1984;Kessler and Lampert 2004), and a variety of other organisms from rotifers (Sarma and Rao 1991) to fish (Cuenco et al 1985). There are far fewer studies dealing with the interaction between food quality and temperature, which has only recently come into focus (Masclaux et al 2009;Sperfeld and Wacker 2009;Persson et al 2011). …”

“…The effect of food quality on zooplankton growth may either increase (Sperfeld and Wacker 2009;Persson et al 2011) or decrease (Masclaux et al 2009) with temperature, depending on the mechanism that determines the quality of the food for the consumer. Dietary deficiency in EPA content has been shown to have greater effect on zooplankton growth and reproduction at lower temperatures (Masclaux et al 2009).…”

“…The effects of constant temperature and intergenerational temperature change on zooplankton abundance have been shown to differ (Verbitskii et al 2009), but most studies of effects of temperature on zooplankton performance and/or food quality constraints were performed at constant temperature regimes (Masclaux et al 2009;Sperfeld and Wacker 2009;Persson et al 2011). The effects of intergenerational temperature fluctuations on zooplankton are poorly understood, and the interactions of these intergenerational temperature changes with food quality are unknown.…”