Meeting Abstract

23.3  Tuesday, Jan. 4  First Description of a Pure-Search Mating System and Protandry in the Caridean Genus Rhynchocinetes BAUER, R.T.*; THIEL, M.; Univ. of Louisiana, Lafayette; Univ. Católica del Norte, Chile rtbauer@louisiana.edu

Previous studies on two gonochoric species of the genus Rhynchocinetes (“hingebeak” shrimps) have described mating systems in which large dominant males with hypertrophied cheliped and third maxilliped weaponry guard and defend smaller females during copulation. In this preliminary study on R. uritai, we report observations indicating a very different sexual and mating system for Rhynchocinetes. A sample of R. uritai taken off Shimoda, Japan, showed a population structure with small males and large females with no overlap in size. Two intermediate-sized individuals showed a mix of transitional sexual characteristics indicating sex change from male to female (protandry): male pleopod characters but female “breeding dress” (incubatory characters) and large vitellogenic oocytes in the gonads, typical of maturing ovaries. Mating observations were made on three receptive females using surveillance video with infrared illumination. Matings occurred at night after female molting. Mating behavior was brief and simple; males approached and attempted to grasp the newly molted female, followed by a brief (~2 sec) copulation, without the complex “caging” (guarding) behavior described for other Rhynchocinetes species. These observations on R. uritai confirm a “pure searching” mating system, with little pre- or postcopulatory interaction between the sexes, a brief copulation and little or no agonistic behavior among males. Such a mating system is characteristic of decapod shrimp species with small males and larger females, as observed in R. uritai. Our preliminary observations strongly suggest that sexual and mating systems, along with sexual dimorphism, vary considerably in the caridean family Rhynchocinetidae.