NECK SPINE PROTECTS DAPHNIA-PULEX FROM PREDATION BY CHAOBORUS, BUT INDIVIDUALS WITH LONGER TAIL SPINE ARE AT A GREATER RISK

We tested the prey preference of Chaoborus sp. on Daphnia pulex with d ifferent defensive morphologies. The protective function of inducible morphological defences, such as neck spine and longer tail spine, was evaluated. Second instar D.pulex individuals of two clones differing i n their strength of neck spine induction were offered as prey to both Chaoborus obscuripes and Chaoborus flavicans. We used logistic regress ion analysis to evaluate the effect of morphometry on the vulnerabilit y of Daphnia. The presence of a neck spine and increased total length protected D.pulex from Chaoborus predation. However, individuals with a longer tail spine were more vulnerable to Chaoborus predation. Chaob orus obscuripes was able to eat daphnids with a neck spine due to the larger gape size of this chaoborid. The smaller species C.flavicans al most always ate prey with no neck spine.