Effects of Experimental Delivery of Male Courtship Pheromones on the Timing of Courtship in a Terrestrial Salamander, Plethodon jordani (Caudata: Plethodontidae)

Male courtship pheromones are chemosignals that affect female receptivity. These pheromones are delivered by the male only after a potential mate has been located and initial courtship interactions have commenced (Arnold and Houck, 1982; Houck, 1986). Thus, these pheromones are distinct from sex attractants, which are usually produced by the female and function to bring potential mates together. Courtship pheromones typically are produced by specialized glands that develop only during the breeding season in sexually mature males. These pheromones are present in many arthropods (e.g., Birch, 1974; Boppre, 1984; Grant et al., 1989) but rarely have been reported for vertebrates (Houck, 1986). Salamanders are a notable exception. The use of courtship pheromones by male salamanders is extremely common (Arnold, 1977; Houck, 1980; Houck and Verrell, 1993). Specialized male courtship glands are widespread in salamander species representing all major lineages (Houck and Sever, 1994), indicating that courtship pheromones play an important role in male mating success. Researchers studying courtship behavior and the development of courtship (mental) glands in salamanders have speculated that courtship pheromones functioned to make the female more receptive to the courting male (e.g., Noble, 1931; Arnold, 1976). This premise was tested quantitatively by Houck and Reagan (1990) for a single species of plethodontid salamanders, Desmognathus ocoee (formerly D. ochrophaeus-, see Tilley and Mahoney, 1996). In D. ocoee, courtship pheromones are delivered by a kind of "injection" system: the male pulls his enlarged premaxillary teeth across the female's dorsum at the same time as his courtship gland swabs the area being scraped (see fig. 8 in Arnold and Houck, 1982). The pheromones presumably diffuse into the female's circulatory system via the capillaries that are superficially abundant in this lungless salamander. The target organ stimulated by the pheromones is unknown. Courtship pheromone effects were tested by applying disks of filter paper (saturated in either a pheromone solution or a saline control solution) to female D. ocoee prior to courtship encounters. Houck and Reagan (1990) showed that courtship time was significantly reduced for those pairs in which the female was reated with the pheromone solution. We have extended the generality of these results by addressing the effects of courtship pheromones in Plethodon jordani, a terrestrial salamander having a very different delivery mode. In P. jordani, courtship pheromones are delivered when the male rubs or slaps his mental gland directly on the female's nares (Organ, 1958; Arnold, 1976). Based on work with a related plethodontid salamander (Dawley and Bass, 1988, 1989; Dawley, 1992), we infer that this kind of direct contact results in the delivery of courtship pheromones to the vomeronasal organ and thus to the accessory olfactory system. For other vertebrates, pheromonal stimulation of the accessory olfactory system has been well documented to affect the expression of reproductive behaviors, including increased receptivity (Singer et al., 1986; Rajendren et al., 1990). We tested the hypothesis that, if a P. jordani pair engages in courtship, female receptivity will be increased following the application of male courtship pheromones. Increased receptivity is operationally defined as a reduction in courtship time relative to control values.