Defenses of the Florida Apple Snail Pomacea Paludosa

1. 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 stable to 5 minutes boiling, but both lose potency after varying lengths of time in water solution. 8. Threshold to intraspecific juice is about .000,000,2 grams crude snail juice per liter. Threshold to Sternotherus minor odor can best be expressed as the amount of water a turtle can make alarming in a given length of time. For a 54 gram Sternotherus minor this figure was about 1500 liters in 10 minutes. 9. Attempts to detect active release of alarm substance in snails stimulated with alarm substance failed. 10. Other species of Pomacea also have analogous (homologous?) alarm reactions. Pomacea dolioides has a response to intraspecific juice similar in its ontogeny to the response of Pomacea paludosa to intraspecific juice, but Pomacea dolioides lacks a response to odor of Sternotherus minor. Pomacea glauca has no response to intraspecific juice but responds strongly to odor of Sternotherus minor during a short period of youth. Both Pomacea glauca and Pomacea dolioides also have alarm responses to mechanical disturbance.