Ephippial and subitaneous egg abortion: relevance for an obligate parthenogenetic Daphnia population

We experimentally analysed the importance of egg abortion in the reproduction strategies of Daphnia pulicaria (Forbes) in Lake Río Seco, a high mountain lake. Adult animals were exposed to different treatments under continuous or dynamic conditions (temperature and photoperiod) to test whether the simulation of field conditions, with changing temperature and photoperiod, induces differences in their reproductive traits in comparison to continuous conditions, with the aim of extrapolating results to the lake. Continuous conditions were the photoperiod and temperature values recorded in the lake at the time when ephippial reproduction is induced. Dynamic conditions were the changing values in the field from the continuous conditions until autumn. The number of healthy ephippial eggs per ephippium was also recorded by using sediment traps in the lake. Our results show that subitaneous and ephippial egg abortion has a major influence on an obligate parthenogenetic Daphnia population in both the laboratory and field. The total number of healthy ephippial eggs per ephippium (mean ± SE; 0.52 ± 0.12) and the proportion of released empty ephippia obtained in the sediment traps (0.73 ± 0.05) were similar to those experimentally obtained under dynamic conditions (healthy eggs per ephippium: 0.29 ± 0.16; proportion of released empty ephippia: 0.79 ± 0.11), suggesting that ephippial egg abortion and empty ephippia production are frequent in nature. This is the first study to describe Daphnia ephippial egg abortion and compare subitaneous and ephippial egg abortion between experimental and field conditions. This approach is recommended for future research into Daphnia or cladoceran reproduction.