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Offspring fitness in Daphnia : Is the Daphnia reproduction test appropriate for extrapolating effects on the population level?
Author(s) -
HammersWirtz Monika,
Ratte Hans Toni
Publication year - 2000
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.5620190720
Subject(s) - offspring , daphnia , reproduction , biology , population , brood , cladocera , daphnia magna , toxicology , zoology , ecology , demography , zooplankton , toxicity , pregnancy , medicine , genetics , sociology
In the Daphnia reproduction test, the number of living offspring per living parent, mortality, and, occasionally, growth and time to first brood are used as endpoints for the determination of no‐observed‐effect concentration (NOEC)/lowest‐observed‐effect concentration (LOEC), or 50% effective concentration (EC50). It is known that chemicals can influence not only the number of neonates but also the offspring size (and, thus, possibly the neonate fitness) in daphnids. Changes in neonate size and fitness have not been routinely recorded in Daphnia reproduction tests, although they are an important factor in population growth. Some of our previous research with some dispersants showed clear effects on offspring quality (smaller neonates with enhanced mortality). We tested one of these dispersants in two different test designs: the reproduction test and a population growth experiment. The results from these two experimental designs differed completely: in the reproduction test, the living offspring number was increased (by up to 10.2 mg/L of the dispersant Dispersogen A) in comparison with the control, whereas in the population growth experiment, the population size was already reduced at concentrations of 1.64 mg/L. A F1‐reproduction test, conducted in control medium with neonates born in the reproduction test, showed that neonate fitness was significantly reduced at concentrations of 1.64 mg/L and higher. Therefore, it appears absolutely necessary to take neonate fitness into account if we intend to assess population‐level effects. This is easily considered in a population growth experiment but not in the Daphnia reproduction test. To evaluate the fitness of the neonates, an additional test with neonates (F1 test) or another test design (population growth experiment) is necessary.