FREEMAN, A. S.; University of New Hampshire: Trade-offs of inducible defenses in blue mussels (Mytilus edulis) in response to multiple predators with differing attack strategies.

Examples of induced defenses in response to simultaneous cues from multiple predators are rare, despite being a more realistic representation of multiple predator environments. I compared the inducible defensive responses of a common marine mussel (Mytilus edulis) to waterborne cues from 2 predators with different attack strategies, the sea star, Asterias vulgaris, and the invasive crab, Carcinus maenas; both individually and together. The mussels showed specific inducible defenses appropriate to these predators attack strategy; mussels increased adductor muscle weight in response to cues from the sea star (a predator that pulls mussel shells open) but increased shell weight and thickness in response to the crushing predatory crab. However, in response to the combined cues from both predators, mussels expressed neither inducible defense and had significantly reduced tissue growth. These have implications for interpreting trade-offs of inducible defenses in multiple predator environments; costs and benefits of inducible defenses should include multiple predator as well as single predator scenarios. In addition, these results suggest that cues from the invasive crab, C. maenas, may interfere with the co-evolved defensive response to the sea star, A. vulgaris, leaving mussels more vulnerable to both predators.