CHEMICALLY STIMULATED RESPONSE BEHAVIORS OF THE SALT MARSH PERIWINKLE, Littorina irrorata: A DISTINCTION BETWEEN BASIC ORIENTATION MECHANISMS

Abstract

The salt marsh periwinkle, Littorina irrorata, exhibits distinct behaviors in response to certain chemical stimuli found naturally in its environment by orienting to avoid danger or locate food. Duval et al. (1994) have described negative behavioral responses to water-borne odors from crushed conspecifics and the blue crab, Callinectes sapidus, the main periwinkle predator in the Chesapeake Bay. The authors also reported positive behavioral responses to Spartina alterniflora, a major food source for L. irrorata and the dominant vegetation along the open water areas of the Chesapeake Bay salt marsh. Although Duval et al. (1994) describe these behaviors as oriented movement it is not clear what type of orientation mechanism was used during the responses. The purpose of this study was to determine the orientation mechanisms used by L. irrorata to respond to chemical stimuli derived from Spartina alterniflora, Callinectes sapidus and crushed conspecifics. This study focused on two types of orientation mechanisms, kinesis and taxis, described by Fraenkel and Gunn (1961.) I predicted that L. irrorata would exhibit a positive kinesis in response to S. alterniflora and a negative taxis in response to both C. sapidus and crushed conspecifics. Snails were placed individually into an observation arena and exposed to a control solution or an extract derived from either S. alterniflora, C. sapidus or crushed conspecifics. The path of movement for each snail was recorded and analyzed to determine the orientation mechanism used. The method applied to determine which of these two mechanisms was used is described by Benhaumou and Bovet (1992). This method consists of measuring the angle of the change of direction, or turning angle, from one point to the next along the path. The mean of the turning angles (mean a) of the pathway indicated whether a kinesis or taxis was used for that individual response. The mean a for each pathway for a treatment was averaged to give the grand mean a for the test group. The results of the pathway analyses indicated that L. irrorata exhibit a positive kinesis in response to S. alterniflora, a negative kinesis in response to C. sapidus, and a negative taxis in response to crushed conspecifics. Water-borne chemical odors from crushed conspecifics may play an important role in warning L. irrorata of nearby danger. Snails are able to respond efficiently by moving away from the potential threat. However, chemical cues may not be as important to L. irrorata when responding to threats of predation by C. sapidus. Other crab stimuli such as tactile or visual cues may be the major signals to which snails respond. This research indicates the importance of chemical signals to marine snails.