Testing the reproductive cost hypothesis with five Brachionus rotifer species under different pH conditions
不同pH条件下5种臂尾轮虫（Brachionus）的生殖代价

The correlations between present fecundity (mx) vs. future survival (lx+1), future fecundity (mx+1) and residual reproductive value (V*x) were studied in five species of rotifers, Brachionus calyciflorus, B. quadridentatus, B. urceolaris, B. patulus and B. angularis under different pH conditions (pH 5, 6, 7, 8, 9, 10). The correlation coefficients of mx vs. lx+1 (survival costs) were positive or negative in early age-classes and were negative for the rest of lifespan. In contrast the correlation coefficients of mx vs. mx+1 (reproductive costs) and mx vs. V*x (residual reproductive costs) varied greatly in the magnitude of correlation coefficients, and the majority showed a negative tendency. These results suggest that under different pH conditions there are survival costs, reproductive costs and residual reproductive costs in rotifers that support the reproductive cost hypothesis. Furthermore, 100% of the regressions of survival cost vs. cohort age-class, 97% of the regressions of reproductive cost vs. cohort age-class and 93% of the regressions of residual reproductive cost vs. cohort age-class were significant, indicating that the negative relationships were stronger in older age classes than in younger age classes. The results also showed that compared to favorable pH levels (neutral pH), the negative correlations of B. quadridentatus, B. urceolaris and B. patulus were more pronounced under stressful pH conditions (acid or alkaline pH).