S11.5  Wednesday, Jan. 6  Sexually dimorphic remodelling of Gambusia^‘s anal fin, body plan, and spinal neural circuitry which facilitates rapid copulatory behavior ROSA-MOLINAR, E.*; LAUDER, G. V.; University of Puerto Rico-Rio Piedras, San Juan, PR; Harvard University, Boston, MA ed@hpcf.upr.edu

For 24 years, our research on the Western Mosquitofish, Gambusia affinis (Gambusia hereafter) has refined and extended prior research on the species and elucidated a mechanism by which the sexually dimorphic modified anal fin, the gonopodium, of the male Gambusia is radically remodelled and anteriorly transposed.� We assert the anterior transposition of the gonopodium aligns the urogenital pore with a permanent dorsal groove of the gonopodium and the alignment is necessary and sufficient for the transfer and deposition of spermatozeugmata within the female urogenital sinus. Three-dimensional kinematics confirm our assertion and extend Peden�s (1975; Can. J. Zool. 53: 1290-1296) and others^� observations of sexually dimorphic copulatory behavior.� We confirm that male Gambusia circumducts the gonopodium without displaying precopulatory behaviors and show that circumduction is a complex movement in which abduction, extension, pronation, and adduction movements are combined in a very rapid sequence. Contrary to previous reports, the sexually dimorphic pectoral fin does not support the gonopodium during copulatory behavior. We elucidated the spinal neural circuitry involved in control of gonopodium circumduction by identifying distinct pools of ^�Golgi-like^� labeled motor neurons innervating anal fin muscles and observing dye-coupling between motor neurons and interneurons.� To better define the nature of the dye-coupling, we employed freeze-fracture replica immunogold labeling for connexin 35. Our results show the presence of connexin 35 immunopositive dendrodendritic gap junctions between motor neurons and between motor neurons and interneurons. Gap junctions^� role may be to increase speed and to increase or decrease synchrony of neural activity of neuronal populations controlling the anal fin muscles. Research supported by NIH-NS30405.