SPYING ON SNAILS: A TEST OF THE 0-1 RULE USING TIME-LAPSE PHOTOGRAPHY

The fossil record suggests that naticid gastropods are size-selective predators, a behavior predicted by optimal foraging theory (OFT). Many live-animal studies agree that behavior exhibited by shell-drilling naticids follows that of energy maximizing predators. The outcome of naticid predation is mainly controlled by predator-prey size ratio and prey shell thickness. In general, naticids exhibit a stereotyped sequence of behaviors when drilling prey. OFT for predators that encounter prey sequentially like Euspira heros predicts the 0-1 rule, in which a quantitative threshold determines whether a predator should either always reject or always consume a given prey type. However, no tests have explicitly shown that naticids will reject a prey type not meeting optimal diet requirements. This study aims to test the 0-1 rule, reveal details on the parameters of prey selection/drilling by E. heros, and investigate if previous drilling experiences affect prey selection. Time-lapse photography is used in order to conduct extended behavioral observations. Individual naticids are maintained in separate 10gal aquaria filled with seawater (18-21°C, normal salinity). Snails will be exposed to 3 prey treatments, each totaling 10 prey items. In treatment 1, predators are given equal amounts of small and large clams, Mercenaria mercenaria. Treatment 2 will present predators with 8 small and 2 large prey items. Treatment 3 will utilize 2 small and 8 large prey items. Because the outcome of predation depends primarily on the predator: prey size ratio, each snail’s small and large prey sizes are specific to that predator. Consumed prey are replaced by another clam from the same size group every 2 days, and a new 48-hour replicate begins using the same snail. After 5 replicates of each of the 3 treatments, a new snail begins testing.

Experiments are ongoing; however, completed trials exemplify the stereotypic behavior of naticids; once a prey item is manipulated, the snail will attempt to drill despite inadvertent physical contact with more valuable prey. Results to date do not support an inflexible 0-1 rule in E. heros. However, the sequence of prey sizes selected by naticids suggests that an adaptive rate-maximization model may be a more realistic depiction of naticid foraging.