P1.28 Wednesday, Jan. 4 The characterization of antifeedant/defensive properties of a Pacific coast opisthobranch Tritonia tetraquetra (Bergh) and its octocoral prey Ptilosarcus gurneyi (Gray) SHAPIRO, NS; CHOATE, BA; HUYNH, MH; MURRAY, JA*; Cal. State U. East Bay; Cal. State U. East Bay; Cal. State U. East Bay; Cal. State U. East Bay email@example.com
Nudibranchs as a clade possess chemical defense mechanisms to deter predation. However, no study to date has assessed the chemical defensive potential of Tritonia tetraquetra or the potential chemical ecology shared between the nudibranch and its octocoral prey species, the sea pen Ptilosarcus gurneyi. A series of antifeedant experiments using Hemigrapsus oregonensis were set up to measure the feeding rate of these crabs when offered tissue from Tritonia tetraquetra and Ptilosarcus gurneyi as well as by gelatin infused with aqueous extracts of either species. The results of feeding assays indicated 36X fewer feeding attempts upon Tritonia tetraquetra tissue (p<0.001) compared to palatable control tissue (chicken). We observed 22X fewer feeding attempts upon Ptilosarcus gurneyi tissue (p<0.001) compared to palatable controls. Furthermore, crabs offered nudibranch or sea pen tissue spent on average <1% of the time feeding, compared to those offered chicken tissue, which spent 45% of the time feeding (~500X difference). Results were similar when the tissue was replaced by gelatin flavored with aqueous extracts of Tritonia or Ptilosarcus (to control for the possible effects of texture and other non-chemical antifeedant properties). A comparison of feeding probability between crabs offered Tritonia-flavored gelatin and Ptilosarcus-flavored gelatin indicated that Ptilosarcus flavor is ~7X less attractive than that of Tritonia (p=0.04). These results indicate some chemical defense which makes both of these species unpalatable to potential predators. This is the first study to positively confirm antifeedant properties in either of these species.