摘要：Laboratory experiments were conducted to evaluate the effects of food phosphorus (P) concentrations on the population dynamics, ephippium production, and resting egg formation of two cladocerans, Moina irrasa and Daphnia similoides , fed on Chlorella vulgaris that were cultured in five different P concentrations (0.05, 0.1, 1, 5, and 10 mg/L). The body length at the first pregnancy of M. irrasa and D. similoides significantly increased with higher P concentration, whereas the maturation time significantly decreased. The maximum population density of M. irrasa (mean ± SD, 6220 ± 1129 ind/L) and D. similoides (1816.5 ± 63.5 ind/L) appeared in the 5 and 10 mg P/L groups, respectively. The maximum male density of M. irrasa (150 ± 113.0 ind/L) appeared in the low P concentration of 0.05 mg/L, whereas it was in the higher P concentrations for D. similoides . The maximum cumulative ephippia number of M. irrasa (51/female) and D. similoides (6.2/female) appeared in the 0.05 and 1 mg P/L groups, respectively. The maximum percentage of ephippia containing resting eggs of M. irrasa (69.3%) appeared in the lowest P concentration. The percentage of ephippia containing resting eggs of D. similoides increased gradually with higher P concentration, and the ratio was above 70% in higher P concentrations (5–10 mg P/L). Our results suggest that low P can advance and induce the production of ephippium in two cladocerans and that higher male density promotes the resting egg formation of cladocerans.
