A gastropod's induced behavioral and morphological responses to invasive Carcinus maenas in Australia indicate a lack of novelty advantage

Evolution has afforded many organisms the capacity to recognize predation threats and respond accordinglywith behavioral andmorphological defenses. Biological invasions may obviate these coevolved recognition systems resulting in biological interactions with native species that range from novelty advantages to disadvantages for the introduced species. Predator recognition initiates responses that can affect other community members through trait-mediated indirect interactions. In this study we use the Australian invasion of a marine, predatory crab (Carcinus maenas) to determine if populations of a native whelk (Haustrum vinosum) with different histories of Carcinus invasion (no previous exposure, 20 years of exposure and 100 years of exposure) recognize and respond to the introduced crab. Haustrum were subsampled from invaded and uninvaded populations then monitored for foraging behavior, shell growth and tissue growth while maintained in a common garden setting with and without waterborne cues from Carcinus. We found that both invaded and uninvaded populations of Haustrum recognize and respond to Carcinus by reducing shell growth and foraging. In feeding experiments, Carcinus showed a preference for small whelks but not thin-shelled whelks. Our results suggest that introduced populations of Carcinus in Australia do not benefit from a novelty advantage and that the induced morphological changes in Haustrum are not a defense, per se. Haustrum’s induced behavioral response to Carcinus may be more important in reducing predation than morphological defenses, and further propagate the invasive crab’s impacts.