Supplementation with Sterols Improves Food Quality of a Ciliate for Daphnia magna

Abstract

Experimental results provide evidence that trophic interactions between ciliates and Daphnia are constrained by the comparatively low food quality of ciliates. The dietary sterol content is a crucial factor in determining food quality for Daphnia. Ciliates, however, presumably do not synthesize sterols de novo. We hypothesized that ciliates are nutritionally inadequate because of their lack of sterols and tested this hypothesis in growth experiments with Daphnia magna and the ciliate Colpidium campylum. The lipid content of the ciliate was altered by allowing them to feed on fluorescently labeled albumin beads supplemented with different sterols. Ciliates that preyed upon a sterol-free diet (bacteria) did not contain any sterols, and growth of D. magna on these ciliates was poor. Supplementation of the ciliates' food source with different sterols led to the incorporation of the supplemented sterols into the ciliates' cells and to enhanced somatic growth of D. magna. Sterol limitation was thereby identified as the major constraint of ciliate food quality for Daphnia. Furthermore, by supplementation of sterols unsuitable for supporting Daphnia growth, we provide evidence that ciliates as intermediary grazers biochemically upgrade unsuitable dietary sterols to sterols appropriate to meet the physiological demands of Daphnia.

Food quality of heterotrophic bacteria for Daphnia magna: evidence for a limitation by sterols

“…In contrast to Daphnia , heterotrophic protists grow efficiently on bacterial diets (Sherr & Sherr, 1984; Fenchel, 1986), which suggests that they do not require a dietary source of essential lipids. Both heterotrophic nanoflagellates and ciliates have been shown to upgrade cyanobacterial carbon for subsequent use by Daphnia , which has been attributed to the de novo synthesis of essential lipids by the protozoans (Martin‐Creuzburg et al , 2005a, 2006; Bec et al , 2006) and/or to the detoxification of cyanobacterial food (Bec et al , 2006). This adds to the general view that heterotrophic protists play a significant role in transferring prokaryotic (picocyanobacterial and bacterial) carbon to higher trophic levels (Sherr & Sherr, 1984).…”

Modulation of longevity in Daphnia magna by food quality and simultaneous exposure to dissolved humic substances

“…Many abiotic and biotic factors determine the natural fluctuations of zooplankton population densities in general, and Daphnia in particular: climatic parameters, such as temperature and light (Berberovic et al 1990;Straile and Geller 1998;Alekseev and Lajus 2009), pH, oxygen conditions, and other water quality parameters (Krause-Dellin and Steinberg 1986), quantitative and qualitative food conditions (Geller 1975;Moore 1980;Rohrlack et al 1999), essential nutritional elements and compounds (e.g., Müller-Navarra 1995;Martin-Creuzburg et al 2006, as well as predation by fish or invertebrates (e.g., Vanni 1986;Lampert 1993). Even these factors create a complex tangle of influences (Gyllström and Hansson 2004); yet, the situation becomes even more complex, since one ecological parameter has not yet been considered as a stressor in depth: dissolved organic carbon, DOC .…”

Stress by poor food quality and exposure to humic substances: Daphnia magna responds with oxidative stress, lifespan extension, but reduced offspring numbers

“…in particular: climatic parameters such as temperature and light (Geller, 1975), oxygen conditions and other water quality parameters, such as acidity (Krause-Dellin & Steinberg, 1986) quantitative and qualitative food conditions (Geller, 1975;Sterner & Schulz, 1998;Giebelhausen & Lampert, 2001;Balseiro et al, 2008), essential nutritional elements and compounds (Müller-Navarra, 1995;Elser et al, 2000;Martin-Creuzburg et al, 2006), as well as predation by fishes or invertebrates (Stich & Lampert, 1981;Vanni, 1986;Mikulski et al, 2004;Pijanowska & Kloc, 2004;Pauwels et al, 2005).…”