Behavioral tests for a possible contact sex pheromone in the caridean shrimp Palaemonetes pugio

Stimuli involved in sexual attraction to and recognition of receptive females by males were investigated in the shrimp Palaemonetes pugio. Newly molted, prespawning (postmolt parturial) females are receptive and attractive to males. Males that make physical contact with a postmolt parturial female, usually with the long antennal flagella, react immediately and dramatically with copulatory behavior. Experiments using females sealed in glass containers suggest that visual Stimuli are not important in mate recognition. To test the role of cuticular texture in sex attraction, males were exposed to females and males of different molting and reproductive states; copulatory responses were recorded. Males copulated with postmolt parturial females in a majority of replicates. Newly molted but nonparturial females, as well as newly molted males, evoked little copulatory response from males. Thus, the soft texture of a newly molted cuticle does not appear important in sex attraction. The duration of attractiveness of postmolt parturial females was measured by exposing them to males at known intervals after molting. There was a steady decline in attractiveness, with copulation in 80% of females within 2 h of the parturial molt, decreasing to 30% in 6-8 h after the molt. The behavioral evidence suggests that males are responding to an insoluble substance (contact sex pheromone) in or on the exoskeleton of the postmolt parturial female. Attempts were made to remove the substance mechanically by rubbing the exoskeleton of postmolt parturial females with small latex sponges, but males showed no response in bioassays. Cuticular hydrocarbons, glycoproteins, or other compounds secreted on the surface through pore canals or tegumental gland openings might serve as sex attractants. A contact sex pheromone in P. pugio and other carideans might also be a substance involved with sclerotization, calcification, or other such chemical changes occurring in the cuticle of the early postmolt parturial female.