Defenses of the Florida Apple Snail Pomacea Paludosa

Abstract1. Pomacea paludosa exhibits a variety of defenses against predation, including aposematic eggs and dropoff-burial responses to odors of turtles, odors of crushed conspecific snails, and mechanical disturbance. 2. The conspicuous pinkish-white eggs are laid out of the water and hatch after several weeks incubation. Distastefulness is strong at first but disappears by hatching time. After hatching, snails are apparently tasty food items for a great variety of predators. The brightly colored eggs of other species of Pomacea may also be aposematic, though we have direct evidence for unpalatability in only one other species, Pomacea dolioides. 3. The self-burial alarm responses to turtle odors and intraspecific juices appear identical in form but are not identical in ontogeny. Response to intraspecific juice is not present on hatching, develops gradually over the first few weeks of free existence, and continues throughout the life of the snail. Burial responses to turtle odors are present in snails prior to the normal hatching date and continue for varying lengths of time after hatching. Response to Sternotherus minor odor continues until snails are about 3 grams in weight; response to Chelydra serpentina odor continues until snails are at least 20 grams in weight. Ontogeny of response to other turtle odors has not yet been investigated, though young Pomacea paludosa have been reactive to odors of all turtles tested to date. 4. The ontogenies of response to Sternotherus minor and Chelydra serpentina odors correlate closely with the abilities of adults of these turtles to eat snails. Adult Sternotherus minor in the laboratory have been unable to eat snails much larger than about 3 grams in weight, while an adult Chelydra serpentina has eaten snails over 20 grams in weight. Snails apparently discriminate between the odors of these two turtles on the basis of qualitative rather than quantitative differences in odor, and preliminary evidence suggests that snails do not discriminate between different-sized turtles within a species. 5. Intraspecific juice is potent in producing alarm in total darkness just as in the light. Response to turtle odors is almost completely inhibited by darkness, red light, or dim incandescent light. 6. Odors of most predators other than turtles produced no response in young Pomacea paludosa. Weak, inconsistent responses were seen to alligator and crocodile odors. 7. Both intraspecific juice and odor of Sternotherus minor are stab