Discrimination of Conspecific Male Molt Odor Signals by Male Crayfish, Orconectes Rusticus

For many organisms, chemoreception plays a key role in numerous aspects of daily life. Crayfish use chemical signals to find mates, warn conspecifics of predators, and relay social status. While many of these situations have been studied in detail, behavior of conspecifics toward chemical signals from molted individuals has not been thoroughly examined. The physiology of crayfish changes dramatically during molting (ecdysis), which in turn may change both the chemical content and concentrations of the chemical cues released into the water. We hypothesized that conspecifics are sensitive to chemicals released during molting. A Y-maze experimental design was used to test for differential responses to various molt-related chemical stimuli presented to intermolt male crayfish (Orconectes rusticus). The sources of chemical stimuli were recently molted male crayfish, intermolt male crayfish, control (aged tank water), and food (fish). Behavioral indices of response included initial arm choice, time spent in each arm, time spent at each nozzle, number of arm changes, and meral spread at each nozzle. Experiments were also conducted where crayfish were presented the same chemical stimuli in each arm to obtain measures of locomotor activity in the different stimuli. In addition, orientation parameters such as walking speed, walking speed to source, and distance to source were analyzed. Intermolt individuals spent more time in the presence of molt signals, although the food stimulus was more attractive than any other stimuli tested. Crayfish showed a significant initial arm choice when molt stimulus was paired with control. During the identical presentation of chemical stimuli, crayfish showed an increase in locomotor activity in the molt and food chemical stimuli than in the intermolt and control chemical stimuli. There were no significant differences in orientation parameters between chemical stimuli. These results show that crayfish can discriminate molted male conspecifics from the other chemical stimuli tested. Chemical signals mediate many behaviors in Crustacea. Crustaceans can use chemoreception to identify and localize food (Derby and Atema, 1982; Moore et al., 1991; Weissburg and Zimmer-Faust, 1994), predators (Willman and Hill, 1994; Keller and Moore, 1999), and conspecifics (Copp, 1986; Zulandt Schneider et al., 2001). Crustaceans appear to release alarm signals through urine secretion (Zulandt Schneider and Moore, 2000). In addition, crustaceans are sensitive to chemicals such as crushed conspecific cues (Hazlett, 1990; Rittschof, 1992; Hazlett, 1994; Pijanowska, 1997). Mate or sex recognition (AmeyawAkumfi and Hazlett, 1975; Hazlett, 1985; Atema, 1986; Dunham and Oh, 1992; Corotto et al., 1999) and social interactions are influenced by chemical signals (Zulandt Schneider et al., 2001). Chemical signals are important for crustaceans because aquatic animals are ‘‘leaky bags’’ (Atema, 1996), where information about the internal state of an animal is transmitted to the external environment via chemical cues, either actively or passively released. Any change in the physiology of a crustacean will cause a subsequent change in the chemicals ‘‘leaking’’ out into the environment. Physiological and physical changes occur during ecdysis, or molting. During ecdysis, crustaceans have increased concentrations of hormones, including ecdysone and 20-hydroxyecdysone, in the hemolymph (Chang, 1995). These hormones initiate many physiological responses such as the reuptake and sequestering of inorganic chemicals and ions, loosening of the old exoskeleton, and the generation of chemicals that form the new exoskeleton underneath the old one (Waddy et al., 1995). 7 JOURNAL OF CRUSTACEAN BIOLOGY, 23(1): 7–14, 2003