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

Abstract

In freshwater systems, many abiotic and biotic factors determine the natural fluctuation of Daphnia spec. populations: climatic and water quality parameters, quantitative and qualitative food quality and quantity, predation, and humic substances. Many factors/stressors act in concert. In this contribution, we supplied Daphnia magna with two different diets (chlorococcal alga Pseudokirchneriella subcapitata and baker's yeast) fed ad libitum and exposed it to an environmentally realistic concentration of humic substances (HSs). Exposure to HSs caused a transcriptionally controlled stress response with studied genes; cat and hsp60, for the latter partial sequences have been identified. Furthermore, the exposure to HSs reduced the antioxidant capacity. Yet, a much stronger oxidative stress is caused by feeding yeast, which reduced the anti-oxidative capacity to values of approximately 50% of the green algal diet. This reduction is most likely due to the yeast's cell wall to resist digestion rather than to the elemental ratio or deficiency in long-chained unsaturated fatty acids, because both diets were deficient in fatty acids with back bones of more than 20 C-atoms. We assume that the biochemical machinery in the gut continuously activated oxygen to cleave the yeast's cell wall and, hence, reduced the antioxidative capacity of the animals. Neither the analyzed oxidant, H 2 O 2 , nor the antioxidants, total apparent ascorbic acid nor free proline, reflected the oxidative stress situations properly. In addition to the stress, HS exposure extended the mean lifespan of algae-fed D. magna, but at the expense of offspring numbers; so did also the pure yeast diet as compared to the algae diet. The first lifespan extension can be explained by the potential of HSs to block the pathway via the insulin-like growth factor 1 (IGF), whereas the second matches the, in aging papers, well described, but Electronic supplementary material The online version of this article (mechanistically poorly understood caloric restriction. Yeast-fed animals, exposed to HSs changed the energy allocation by reducing life span, but increasing offspring numbers. With the lifespan and offspring numbers, ecologically relevant parameters are differently affected by the simultaneous action of two environmentally relevant stressors.

Effect of tannins on survival and development of Daphnia menucoensis and the abundances of bacteria

“…[43] Whereas other results indicated that humic substances at low concentrations had the potential to expand the lifespan of D. magna, those same findings also demonstrated that the number of offspring was reduced. [44] Similar negative results were also obtained with the cladoceran Ceriodaphnia dubia [19] or with Latonopsis australis [45] although positive effects of polyphenols were, in fact, reported for specific clones of Moina macrocopa [46,47] and for Daphnia magna at low polyphenol concentrations. [48] Humic substances therefore have been shown to alter the lifespan of the cladocerans.…”

Natural dissolved humic substances increase the lifespan and promote transgenerational resistance to salt stress in the cladoceran Moina macrocopa

“…An array of oxidative stress symptoms have been reported in several organisms exposed to HS. These symptoms include reactive oxygen species accumulation and reduced antioxidant capacityeven at very low HS concentrations, membrane lipid peroxidation, and increased activity of antioxidant enzymes (Timofeyev et al 2006a, b;Steinberg et al 2010a). Therefore, Steinberg et al (2003) coined the oxymoron "natural xenobiotics" for HS in relation to their interactions with the biota-in analogy to secondary plant compounds; yet, in contrast to the latter, HS are not synthesized to defend against herbivory, but challenge any exposed organism.…”

Impact of two different humic substances on selected coccal green algae and cyanobacteria—changes in growth and photosynthetic performance

“…HuminFeed® consists of 82% humic substances and 18% low-molecular-weight compounds, and it also contains 43% organic carbon ). It has displayed direct effects on aquatic and sediment organisms including the water mould Saprolegnia parasitica Coker , the water flea Daphnia magna Straus (Euent et al 2008;Bouchnak and Steinberg 2010;Steinberg et al 2010a), Moina macrocopa Straus (Suhett et al 2011), Moina micrura Kurz (Steinberg et al 2010b) and the nematode Caenorhabditis elegans Maupas ).…”

“…Dissolved HSs are taken up by some exposed organisms (Wang et al 1999;Steinberg et al 2003) and interact at various biochemical and molecular levels (for reviews, see Steinberg et al 2006Steinberg et al , 2008. Since HSs are natural xenobiotics and aquatic organisms try to get rid of them after their internalization, it is not surprising that HSs induce anti-stress reactions which consume energy and are-at least in part-transcriptionally controlled (Menzel et al 2005;Steinberg et al 2010a). Eventually, this stress can be lethal (Steinberg 2003;Cazenave et al 2006;McMaster and Bond 2008).…”