Reference: Biol. Bull. 185: 174-185. (October, 1993) Spermatophores and Plug Substance of the Marine Shrimp Trachypenaeus similis (Crustacea: Decapoda: Penaeidae): Formation in the Male Reproductive Tract and Disposition in the Inseminated Female RAYMOND T. BAUER AND LIN JUN MIN Department of Biology, University of Southwestern Louisiana, Lafayette, Louisiana, 70504 Abstract. Sperm are packaged into many small sper-matophores of variable size in the median vas deferens (MVD) of the male. A substance is intermixed with sperm in the proximal coils of the MVD, separating groups of sperm that will be ejaculated as spermatophores. Most of the ejaculatory duct is occupied by a chamber filled with a transparent, viscous fluid termed the "plug substance." When males are artificially ejaculated, spermatophores are emitted, followed by plug substance that quickly so-lidifies. This latter material fills and stoppers a space on the female, the median pocket, which serves as an ante-chamber to the apertures of the internalized seminal re-ceptacles, where sperm from ruptured spermatophores are stored. The slit-like openings to the receptacles are func-tionally divided into a posterior aperture, stoppered by plug substance after insemination, a closed mid-section, and an anterior exit for sperm release during spawning. Direct insemination by an everted male gonopore is considered more likely than transmission of spermato-phores and plug substance via the male gonopod (pe-tasma). In addition to its hypothesized roles during in-semination and sperm release, the mass of plug substance (mating plug) may act as a paternity assurance device that prevents subsequent inseminations by other males. Introduction There is considerable variation in the form and com-plexity of materials transferred from the male to the female during insemination in penaeoid shrimps (Decapoda: Penaeoidea) (Bauer, 1991). Sperm may be packaged in Received 18 December 1992; accepted 14 July 1993. Contribution No. 40 of the USL Center for Crustacean Research. structurally complicated spermatophores composed of an assortment of accessory substances secreted in the male reproductive tract. The most complex spermatophores are those attached externally to the genital area, or thelycum, of the female, as in the white shrimp, Penaeus setiferus, and other species of the subgenus Litopenaeus (Perez Far-fante, 1975; Bauer and Cash. 1991; Chow et a/.. 1991). In contrast, in the rock shrimps, Sicyonia spp., sperm in a seminal fluid are produced by the male and transferred to, and stored in, internal seminal receptacles of the female (Clark et al, 1984; Perez Farfante, 1985; Bauer, 1991, 1992). Other penaeoid shrimps, such as Trachypenaeus spp.. show intermediate degrees of spermatophore com-plexity and of internalization of sperm storage (Burken-road, 1934: Heldt. 1938a, b; Hudinaga, 1941; Malek and Bawab, 1 9 74a, b; Perez Farfante, 1971. 1982; Champion, 1987; Bauer and Cash, 1991). Detailed knowledge of the nature and formation of spermatophores and associated substances and of their disposition in the inseminated female is essential to an understanding of the mechanics of insemination, sperm storage, and sperm release during fertilization. In addition, characters associated with spermatophores and the in-semination morphology of the male and female are im-portant in analyses of the evolutionary relationships among taxa of penaeoid shrimps, as well as to an evolu-tionary interpretation of their mating systems (Bauer, 1991). Observations on the spermatophores, seminal recep-tacles, and thelyca of various species of Trachypenaeus (Penaeidae) have been made by Andrews ( 1 9 1 1), Burken-road (1934), Kubo (1949), Perez Farfante (1971), and Bauer (1991). The structure of the Trachypenaeus sper-174
Spermatophores and Plug Substance of the Marine Shrimp Trachypenaeus similis (Crustacea: Decapoda: Penaeidae): Formation in the Male Reproductive Tract and Disposition in the Inseminated Female
BioStor
