Predator–prey interactions structure ecological communities, and personality can significantly mediate these interactions. Personality expression is often contingent on social context, suggesting that group personality may be key in determining the outcomes of predator encounters. Here we test the influence of individual personality and group composition on survival of the marsh periwinkle, Littoraria irrorata, when exposed to its main predator, the blue crab, Callinectes sapidus, both integral players in mediating the productivity and health of salt marsh ecosystems. Personality varied along a bold-shy continuum and was unrelated to shell length, though neither trait influenced survival when individual snails were exposed to a predator. However, when snails were partitioned into groups differing in personality composition, snails in groups with bold individuals had higher survival than those in groups with none. While group type did not influence the survival of bold snails, shy snails performed significantly better in mixed groups: the presence of a few bold individuals emerged as especially effective in decreasing mortality of shy snails. The effect of personality on predator escape is thus conditional on group personality composition, indicating that social context can directly impact the survival and success of its individual members, with broad implications for community dynamics. 

Littoraria irrorata were haphazardly collected from a salt marsh at UNCW’s Center for Marine Science (34.1418° N, 77.8674° W). They were transferred indoors and housed in groups of 15 within mesh containers (14.60cm x 7.6cm, 0.95L) that sat on a platform in a 37.85L aquarium at a height which allowed each container to have access to both 3 cm of seawater and 6 cm of air.

In each trial, five snails were placed in a single 11.4L bucket (d=18.5cm, h=29cm), filled with 3cm of high-quality seawater and two refuges. The refuges consisted of a hollow semi-sphere placed flush to the bottom of the bucket with an opening of 3cm x 3cm facing the center of the bucket, which allowed snails to freely crawl in and out. Snails were placed in the center of the bucket, equidistant from one another and from the edge, and were allowed to acclimate for five minutes. Behavior was recorded every 2 minutes during the 10-minute trial and here boldness was calculated as the total time in 2-minute blocks where snails were outside the refuge.

In this first set of experiments, a single snail and a single blue crab were simultaneously placed on opposite sides of the tank, and mortality was assessed after a 24-hour period. Trials were run on 25 shy snails and 25 bold snails using a randomly chosen blue crab from the set of nine that were held in 37.85L tanks and fed crushed marsh periwinkles ad lib. for the duration of the trials. In the second set of experiments, 20 snails and a single blue crab were simultaneously placed on opposite sides of the tank, and mortality was assessed after a 72-hour period. Here group personality composition was modified, resulting in five treatments: (a) 20 shy snails, (b) 20 bold snails, (c) 15 bold:5 shy snails, (d) 5 bold:15 shy snails, and (e) 10 bold:10 shy snails.