Breeding ecology and male spawning success in two hill-stream populations of the freshwater goby,Padogobius martensi

Abstract

This investigation was carried out at two study sites to examine the influence of shelter availability, nest site quality and male body size on spawning success of malePadogobius martensi. At Stirone Stream (first study site) individuals were not randomly distributed with respect to usable stones; larger males and females were consistently found to occupy larger stones. Laboratory experiments showed that the bottom surface area of the shelter was the relevant cue for the choice. The number of nesting males settled in a given area increased with increasing availability of local stone cover; inter-nest distance was directly correlated with male size. At Rivarolo Stream (second study site), which was characterized by lower nest density and a greater shortage of large stones, the pattern of shelter occupation was similar. These results suggest the presence of competition among individuals for the possession of larger-sized shelter sites. At both sites, the number of eggs in the nest increased as stone size increased; however, at the first study site, male body size played a major role in male spawning success as it concerns both the numbers of females mated and the number of eggs, while at the second study site, male body size was not shown to influence male spawning success. Factors responsible for between-site differences in male spawning success are discussed.