Meeting Abstract

P1-51  Monday, Jan. 4 15:30  Description of the male genital papilla in the California grunion, a silverside fish that spawns on sandy beaches ARYAFAR, H; CARRILLO, A; BERQUIST, R; FRANK, L; VELASCO, B; FORSGREN, K; DICKSON, K*; California State University, Fullerton; California State University, Fullerton; University of California, San Diego; University of California, San Diego; California State University, Fullerton; California State University, Fullerton; California State University, Fullerton kdickson@fullerton.edu

The California grunion, Leuresthes tenuis, exhibits unusual reproductive behavior in which adults spawn on sandy shores and the externally fertilized eggs develop within the sand. Spawning occurs at night during spring high tides in March-August. Females deposit eggs ~8-10 cm deep within the sand while males release sperm as they surround females at the sand surface. Fertilized eggs incubate in the sand until a subsequent spring high tide washes them out and triggers hatching. While extracting gametes for other experiments, we noticed a small structure protruding from the genital pore of male, but not female, grunion. A subsequent investigation using magnetic resonance imaging, dissections, and histology allowed us to morphologically characterize this muscular genital papilla. The structure could not be found in female grunion, using the same imaging and histological techniques. Therefore, we hypothesize that the structure represents a sexually dimorphic trait in L. tenuis, which may be used to identify males noninvasively even after individual fish have released their gametes. We also hypothesize that the genital papilla represents a specialized structure that evolved in male grunion to eject sperm under pressure so that they can fertilize eggs that the females have deposited within the sand, unlike in other fishes in which such structures are used for internal fertilization.