Contact Sex Pheromones in Shrimps (sponsored by NOAA Louisiana Sea Grant Program)

                                                 female with ripe ovary


Many shrimps mate just after the female molts.  In caridean shrimps, the female must have a mature or "ripe" ovary, i.e., one full of eggs ready to spawn (this is a female of Palaemonetes pugio, a common brackish-water "grass" shrimp in the U.S. Gulf of Mexico, a good model organism to study mating and sex attraction)


                                       male touches female with long antennal flagellum


Just after the female molts, she is attractive to males that touch her with the long whip-like antennal flagellum (smaller male on left)


palaemonetes mating      Click here to view P. pugio mating

The male then grasps the female and mating occurs (from Berg and Sandifer, 1984, Journal of Crustacean Biology)


                                      female with embryos

Two to three hours after mating, the females spawns and the fertilized eggs (now developing embryos) are attached below the abdomen of the female for incubation:

Many behavioral observations on shrimps indicate that the antennal flagellae of these shrimps are chemotactile, i.e., bear taste and touch receptors.   Males must touch the newly molted female to recognize her as ready to mate, so the stimulus could be either a textural one (soft cuticle of the newly molted female) or a chemical one (a non-soluble substance on the surface of the female).  Through a series of behavioral experiments, we (Caskey and Bauer, 2005, Journal of Crustacean Biology), determined that neither visual nor textural cues were used by males.  Rather, all the evidence so far indicates that a compound (contact sex pheromone) on the female's surface is the cue used by males.

Jody Caskey, a graduate student in my lab, has determined that the attractiveness of females declines steadily after the molt during a period of 8 hours, after which the female spawns spontaneously if denied access to a male.  In some other shrimps, the period of female attractiveness may be longer, as long as 24 hours (Bauer, 1979a).  These observations may indicate that some compound associated with cuticular hardening is the chemical signal; alternately, the female may secrete the compound(s) onto the surface via cuticular pores.

                                          duration of female attractiveness

 In many insects, such as the fruit fly Drosophila and certain beetles, males recognize a reproductive female ready to copulate on the basis of surface hydrocarbons, perceived the chemosensory antennae.  These are contact sex pheromones because they are not volatile: the male make contact (taste them) with the antennae.  We are looking, with help of funding of the National Oceanic and Atmospheric Administration (NOAA) Louisiana Sea Grant Program (grant R-SA/03), for such surface compounds that may be a contact sex pheromone in these shrimps.  We are using a combination of surface chemistry studies, behavioral assays, and morphological investigation of possible sensilla (sensory setae or hairs) on the shrimp's antennal flagellum (See Caskey and Bauer, 2005; Bauer and Caskey, 2006)

Publications related to this project:

Caskey, J.L. and R.T.Bauer.  2005. Behavioral tests for a possible contact pheromone in the caridean shrimp Palaemonetes pugio. Journal of Crustacean Research 25: 571-576.

Bauer, R.T. and J.L. Caskey.  2006. Antennal flagellar setae of decapod shrimps: sexual dimorphism and possible role in detection of contact sex pheromone. Invertebrate Reproduction and Development 49: 51-60.

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