Are there allelopathic interactions in zooplankton? Laboratory experiments with Daphnia

Daphnia hyalina and Daphnia cucullata were kept in flow-through chambers in lake water (I), water from mass cultures of D. hyalina (II) and water from mass cultures of D. cucullata (III). A good correlation between body length and clutch size of the Daphnia was found in all cases. The regression lines of the different treatments were compared with respect to different slopes and different intercepts. D. hyalina showed the same reaction to medium II and III, but a lower regression coefficient and higher intercept in medium I. In contrast D. cucullata showed the same reaction to medium I and II, but a higher regression coefficient in medium III.