The influence of reproductive mode and its genetic consequences on the responses of populations to toxicants: A case study

Uniformity in response of test populations has long been an important consideration in the development of toxicity and ecotoxicity tests. We employed the brine shrimp Anemia as a model organism to examine the influence of reproductive mode and its genetic consequences on the response uniformity of test populations to toxicant exposure. We measured growth in four obligately parthenogenetic populations (Artemia parthenogenetica) and three sexual populations (two A. franciscana and one A. urmiana) at three copper concentrations. For parthenogenetic populations, offspring from several females were tested whereas full-sib offspring from single mating pairs were used for sexual populations. We found that Anemia derived from geographically distinct populations of the same species responded similarly to copper exposure. Although there were significant differences in the shape of the concentration-response curves among the three species tested, these differences were not related to reproductive mode. Interactions between clone and copper treatment were a significant source of phenotypic variability for the parthenogenetic populations and accounted for up to 20% of the total phenotypic variance. Residual variability among individuals (within-clones) accounted for the largest percent of the total phenotypic variability, ranging between 55 and 84%. Different clones within parthenogenetic populations differed as much from each other in their response to copper as did different families within the sexual populations. Furthermore, within-treatment random variation among individuals was generally not significantly lower within single clones than within families of genetically mixed offspring. The results of this case study cast doubt on the notion that the employment of genetically uniform populations offers a substantial advantage in terms of increasing the phenotypic homogeneity of a test population's response to toxicant exposure. The primary advantage of asexual populations is that they can facilitate the identification and quantification of important sources of variability in phenotypic responses to toxicants-an issue that remains in need of study. Copyright.