Effects of test media on reproduction inPotamopyrgus antipodarumand of pre-exposure population densities on sensitivity to cadmium in a reproduction test

Abstract

Molluscan species can be affected by various anthropogenic substances. Yet, these effects are disregarded in chemical risk assessment as molluscs are unrepresented in standard OECD guidelines. The project "validation of a mollusc reproduction test" (Federal Environment Agency, code 371165417) deals with the development of a test method with the mudsnail Potamopyrgus antipodarum for OECD purposes. In this context, the influence on reproduction of both, different media and varying snail density, has been observed in independent experiments. Further, the impact of density on the outcome of subsequent cadmium (Cd) toxicity in a test has been investigated to refine the existing methodology. First, adult snails were kept in different test media for 12 weeks. Second, snail density was increased for 4 weeks to induce stress. Snails from each density scenario were used for another 4 weeks in a reproduction test at an equal density with 12 μg Cd/L, respectively. Significant differences in reproduction between medium groups were noted after 4 and 8, but not 12, weeks. Further, reproduction was significantly altered by snail density in the beakers but after subsequent 4 weeks at a constant density, no differences were observed between control groups. Cd reduced reproduction and this effect increased with snail density in the pre-exposure period, demonstrating that a previous stress factor may result in increased sensitivity to chemicals and underlines the need for more standardized breeding conditions to minimize effect variations. Based on the outcome of this study, an acclimatization period of 12 weeks must be guaranteed for specimens transferred to another medium. Further, 4 weeks of acclimatization are necessary after density stress. An additional 12 weeks density experiment showed that medium volume in each replicate can be decreased by half to save on chemicals, water and space during tests.

Profound Effects of Population Density on Fitness-Related Traits in an Invasive Freshwater Snail

“…Profound effects of population density on embryo production were even observable between treatments differing in density by only one snail, exemplified by the ∼162% higher embryo production of individuals in the seven-snail treatment relative to individuals in the eight-snail treatment. While another recent study of the influence of population density on reproduction in P. antipodarum also showed that reproductive output increased at intermediate densities [13] , our study is the first to show that this phenomenon occurs in the absence of systematic changes in food availability across density treatments.…”

“…Here, our goal was to provide an in-depth characterization of the relationship between population density, growth rate, and reproductive output in P. antipodarum . Our main points of departure from similar studies conducted by Neiman et al (2013) [11] and Sieratowicz et al (2013) [13] are 1) the combined use of a wide range of population densities and precisely controlled food administration, 2) individual-level variation in population density, and 3) the inclusion of two genetically distinct lineages. Because growth and reproduction in P. antipodarum is very sensitive to food availability [11] , parsing out direct effects of population density requires that food availability does not vary across density treatments.…”

“…While these studies have certainly provided important advances, the growing body of evidence that P. antipodarum is very sensitive to environmental variables like food availability [11] , population density [11] – [13] , temperature [7] , [14] – [15] , and dietary nutrient content [10] , [16] means the careful use of P. antipodarum as a model system requires a thorough understanding of how fitness-related traits are influenced by environmental conditions [13] . A number of recent studies have made a great deal of progress in this direction [7] , [10] – [11] , [15] – [17] , but critical questions remain.…”

“…A number of recent studies have made a great deal of progress in this direction [7] , [10] – [11] , [15] – [17] , but critical questions remain. For example, despite the complex relationship between P. antipodarum reproduction and population density [11] – [13] and the clear sensitivity of P. antipodarum to food availability [11] , no study has simultaneously controlled per-capita food and measured the response of fitness-related traits across a series of population densities. As such, we still do not have a clear understanding of the nature of the relationship between population density per se and fitness-related traits in P. antipodarum or know whether the positive relationships between population density and reproductive output observed in Neiman et al (2013) [11] and Sieratowicz et al (2013) [13] extends to the much higher population densities often used in ecotoxicology studies ( e.g.…”

“…Furthermore, because most studies of the relationships between fitness-related traits and environmental variables in P. antipodarum do not include individuals from multiple genetically distinct asexual lineages ( e.g. , [10] – [13] ), the extent to which the conclusions of these studies apply across this notably diverse species [20] , [21] remains unclear.…”