Life-history responses of a freshwater rotifer to copper pollution

<p class="normal">In organisms with dormant stages, life-history responses to past pollution can be studied retrospectively. Here, we study such responses in a rotifer (<i>Brachionus calyciflorus</i>) from the once heavily copper-polluted Lake Orta (Italy). We extracted resting eggs from sediments, established clonal lineages from hatchlings, and exposed newborns of these lineages to one of three copper concentrations that each mimicked a specific period in the lake's pollution history. For each rotifer, we daily collected life-table data. We then estimated treatment-specific vital rates and used a stage-structured population model to project population growth rate <i>λ</i>. We also estimated elasticities of <i>λ</i> to vital rates and contributions of vital rates to observed Δ<i>λ</i> between copper treatments. As expected, <i>λ</i> decreased with increasing copper concentration. This decrease resulted mostly from a decline in juvenile survival rate (<i>S_J</i>) and partly from a decline in the survival rate of asexually reproducing females (<i>S_A</i>). Maturation rate, and with one exception fecundity, also declined but did not contribute consistently to Δ<i>λ</i>. <i>λ</i> was most elastic to <i>S_J</i> and <i>S_A</i>, indicating that survival rates were under stronger selection than maturation rate and fecundity. Together, our results indicate that variation in juvenile survival is a key component in the rotifers' copper response. The consistent decrease in <i>S_J</i> with increasing copper stress and the sensitivity of <i>λ</i> to that decrease also suggest that juvenile survival is a useful indicator of population performance under environmental pollution.</p>