Ovulating Female of Nine‐Spined Sticklebacks ( <i>Pungitius sinensis</i> ) Are Attracted to Substances Derived From Male Kidneys

Male sticklebacks (Gasterosteidae) produce an adhesive protein called "spiggin" in the tubular epithelial cells of their kidneys, which they use to attach plants or plant debris together and build nesting sites. Spiggin is a glycoprotein excreted in urine. A similar substance has been reported in freshwater sculpins (Cottidae), and it is thought that male sculpins that nest under stones use this glycoprotein in their enlarged kidneys to attract females to their nests. Based on the phylogenetic closeness of sticklebacks and sculpins and the physiological similarities in their kidneys, we hypothesized that spiggin may play a role in attracting females to nesting sites in sticklebacks. We tested this hypothesis using a Y-maze with the nine-spined stickleback (Pungitius sinensis), a member of the Gasterosteidae. Ovulated females were more consistently attracted to male kidney extracts than female kidney extracts. The high-molecular-weight fraction (molecular weight > 3000) separated from the male kidney extract using a dialysis membrane had an attractive effect on ovulating females, while the low-molecular-weight fraction (molecular weight < 3000) had a repellent effect. The water in the aquarium containing nests built by males significantly attracted ovulating females. These results suggest that spiggin or an unknown component associated with spiggin functions to attract ovulating females. In sticklebacks, which evolved from territorial breeding to building elaborate nests, it is possible that the substance that attracts females produced in the male kidney has evolved into an adhesive component that solidifies the nest.