Sexual Kidneys in the Red-spotted Newt (Notophthalmus viridescens)

Abstract Functional nephrons of the kidney with secondary sexual function are rare in vertebrates and descriptions of these structures do not unequivocally conclude that they aid in reproduction. This statement holds true for the collecting ducts of the pelvic kidneys in male salamanders, which appear to synthesize abundant secretory material during times of reproductive activity. To indirectly test the hypothesis that collecting ducts of the pelvic kidneys in salamanders are indeed secondary sexual structures, we investigated the correlation of collecting duct secretory activity with that of the seasonal secretory and growth cycles of three known secondary sexual structures: genial glands, dorsal glands of the cloaca, and tail. Male Red-spotted Newts (Notophthalmus viridescens) were captured every month and their urogenital organs were processed for general histological examination. To quantify the seasonal activity of the pelvic kidney collecting ducts, we measured the epithelial height of the collecting ducts, by month, and compared these data with the epithelial heights of the genial glands and dorsal glands and tail depth. The data indicate that there is a significant correlation between the seasonal secretory activity of the collecting duct epithelium and the seasonal activity of previously identified secondary sexual structures. Previously identified secondary sexual structures increase in epithelial height and tail height during the fall, winter, and spring and the collecting duct epithelium mirrors these increases directly. The strength of this correlation provides novel evidence that the salamander kidney collecting ducts may function as secondary sexual structures. However, the actual function of the secretions remains unknown.