Impact of male and food density on female performance of the brackish cladoceran Daphniopsis australis
Résumé
The roles of male and food density in regulating female performance were investigated in the brackish cladoceran, Daphniopsis australis. Parthenogenetic females and ephippial females were tested using a 2 × 4 factorial experiment involving the presence and the absence of a male cross-classified with nil, low, medium and high food densities. For parthenogenetic females, the male presence and food density failed to trigger the switch from asexual to sexual reproduction, but the presence of male negatively affected parthenogenesis through egg abortion. Food density affected the animal longevity but depended on the male presence. The reproductive output was favoured by increasing food densities, but the male presence increased egg abortion, suggesting male being an added stress factor to parthenogenetic females. For ephippial females, food densities affected the frequency of switch from sexual to asexual modes in the absence and the presence of a male. However, the male enhanced switch frequency under low and high food densities. Longevity was increased with the male presence but was unaffected by food density. The ephippial females successfully produced diapausing eggs with the male presence. Although, ephippial females could switch to parthenogenesis but the reproductive output of switched ephippial females was inferior to that of parthenogenetic females since birth. The results reveal that the male presence and food density can impact the performance of female D. australis. Hence, this study provides an insight into the understanding of the reproductive biology of cladocerans and a possible alternative explanation for population dynamic of this species and other cladocerans in the field.