Chaoborus predation on typical and spined morphs of Daphnia pulex: Behavioral observations’

Behavioral observations of Chaoborus americanus predation on juvenile instars of typical and spined forms of Daphnia pulex were used to answer two questions: Does the spincd morph (SM) have a higher escape efficiency than the typical morph (TM)? Is handling time of ingested SM longer than that of TM? Results indicate that SM was clearly superior to TM in escaping the grasp of both third and fourth instar Chaoborus larvae and visible injuries to escapees were rare. The escape efficiency of larger Daphnia was higher than that of smaller Daphnia when tested with fourth instar Chaoborus. Differences in handling time for the two morphs could not be demonstrated. Handling times were short but highly variable, being partly dependent on Chaoborus length and orientation of the prey item. Within the range of 0.8-1.3 mm, Daphnia body length had no discernible influence on handling time. Krueger and Dodson (198 1) showed that Daphnia minnehaha Herrick was an induc-ible morph of Daphnia pulex Leydig, 186