Variation in Chemical Composition, Reproductive Success and Body Weight of Daphnia magna in Relation to Diet

Abstract

The concern of this stndy has been the chemical composition of Uaphnia omgnu, the algae (Selenustrum, cnpricornutuni, Ankistrodesmus convolutus) it was fed, the two growth media in which the algae were cultured and the water (Lake Huron, Michigan, USA) in which D. magnu was reared. A synthetic diet (fish chow+alfalfa) was used as a control. The effectiveness of these five diets on the health of the 1). inagna populations was ascertained by t,he weight and number of neonates thus produced. The diet, S. capricornufuin cultured in an organic medium, prodnced the largest mean brood size and the heaviest neonates in unstressed populations. The synthetic diet prodnced the smallest mean brocd size and the lightest neonates. Stressed organisms may produce smaller broods wit.h heavier neonates than unstressed organisms. The erolnticnary significance of this observation is discussed. Statistical studies suggetit that daphnids maintained on the synthetic diet derired no demonstrable nutritive value from the diet in terms of elemental composition or amino acid production. A great similarity in patterns cf amino acid quantity and type was noted in the algae and the daphnids. On further examination it was discoverctl that this pattern was widespread in other aquatic forms, bacteria, fungi, yeasts, casein and was common t o a variety of birds and mammals. It may be suggested that products that are made and stored, such as lipids. are less uniform in pattern among widely diverse species than those that have t o he produced and are not stored. such as amino acids.

A Comparison of the Effect of Four Benchmark Chemicals on Daphnia Magna and Ceriodaphnia Dubia-Affinis Tested at Two Different Temperatures

“…Since toxicity tests are carried out with the intent of protecting the environment from the introduction of alien and toxic substances, results are more likely to simulate the field condition if test organisms resemble those encountered in nature. The D. mugnu population utilized in this study is similar in chemical composition to those collected in the field [15,16]. The C. dubiduffinis population is still too new to permit such comment.…”

Food Web Paradigms: The Biochemical View on Trophic Interactions

“…However, different to elements which cannot be converted into each other, required knowledge on the conversion and thus substitutability of biochemical constituents makes biochemical stoichiometric applications more difficult. COWGILL et al (1986) report a great similarity between the amino acid composition of the food and the daphniid consumer, which suggests low conversion capabilities in this zooplankton group. However, no or only a restricted food dependent influence in the amino acid pattern of consumer was found for the rotifer Brachionis plicatilis (FROVLOV et al, 1991) and females of the harpactoid copepod Euterpina acutifrons and its eggs (GUISANDE et al, 2000) but egg production and hatching success was enhanced if egg and female matched food amino acid composition in the later case.…”

Whole effluent toxicity testing—usefulness, level of protection, and risk assessment

“…Each of these modifying factors can affect an organism's response to toxicants. For example, differences in diet [34][35][36][37][38][39][40], temperature [30,41], and water quality [42][43][44] can affect the results of toxicity tests with daphnids. Such is also the case for other organisms.…”