THE CLONAL ECOLOGY OF HETEROCYPRIS-INCONGRUENS (OSTRACODA) - LIFE-HISTORY TRAITS AND PHOTOPERIOD

1. The coexistence of different clones and, in general, the clonal str ucture of parthenogenetic populations have been linked to differences in the ecological requirements. 2. Previous field and laboratory work demonstrated the effect of temperature on the seasonal succession of e lectrophoretic clones of Heterocypris incongruens in an Italian ricefi eld. 3. Here we report the results of laboratory experiments on the ef fect of photoperiod on life-history traits (age and carapace length at first reproduction, age at death, number of resting and total eggs) o f these clones. 4. Clonal differentiation is greater at 16:8 L:D than at 12:12 L:D. 5. The winter clone responds to longer light hours by sl owing down its growth and producing a larger number of resting eggs. I n contrast, the summer clone, when exposed to long days (16:8 L:D), ha s faster growth and higher survival while producing almost no resting eggs. 6. No clear effect of photoperiod was found in a clone rare in t he field in all seasons. 7. The pattern of response to longer daylight hours validates the hypothesis of an important role of photoperiod in determining the seasonal clonal succession observed in the field.