Potential multiple functions of a male sea lamprey pheromone.

Introduction The sea lamprey is a useful animal model for understanding the role of olfactory communication in reproduction (Teeter, 1980; Li et al., 2003a). Our research has focused on characterizing the structure and function of pheromones that signal mating readiness in adults. Sexually mature sea lampreys are virtually blind (Manion and Hanson, 1980), cease feeding (Larson, 1980) and likely coordinate mating and spawning activities through chemical cues (Li et al., 2003a). Previous studies have indicated that both male and female sea lampreys release pheromones to attract individuals of the opposite sex (Teeter, 1980). We reasoned that the male pheromone would be technically advantageous to isolate and identify. This pheromone has to be released in a large quantity to be effective because males move into the spawning grounds first and then release a pheromone to guide the females to their nests (Teeter, 1980), which are often built in rapids where flow rates range between 0.5 and 1.5 m/s (Manion and Hanson, 1980). Further, identification of a male sea lamprey pheromone could provide a model system for studies of male pheromone signaling in fish. Several hormonal pheromones have been identified in female teleosts but not in males (for a review, see Stacey and Sorensen, 2002). Structure and function of male pheromone compounds Two novel bile acids, 7α,12α,24-trihydroxy-3-one-5α-cholan-24-sulfate (3kPZS; Li et al., 2002; Yun et al., 2002) and 7α,12α-dihy-droxy-5α-cholan-3-one-24-oic acid (3kACA; Yun et al., 2003), have been postulated to be components of the male pheromone based on several lines of evidence (Li et al., 2003a). First, these two compounds are released only by male lampreys after the onset of spermiation (Yun et al., 2002, 2003; Siefkes et al., 2003b) and it is only spermiating males that releases the male pheromone (Li et al., 2002; Siefkes et al., 2003a,b). These results corroborated previous findings that sexually mature males release a pheromone that attracts sexually mature females (Teeter, 1980) and that water wash-ings from spermiating males are more stimulatory to adult olfactory organs than those from pre-spermiating males (Bjerselius et al., 1996). Secondly, when measured with electro-olfactogram (EOG) recording, mature female sea lampreys detect 3kPZS and 3kACA at concentrations as low as 10 –12 and 10 –10 molar, respectively (Siefkes and Li, 2004). Thirdly, at ∼1.7 × 10 –10 molar, 3kPZS induces robust preference and search behaviors in ovulated females placed in a two choice maze (Li et al., 2002). These behaviors are the same …