Variation in male mating success in the paternal nest brooder, Rhinogobius goby, along a river course

Abstract

AbstractRhinogobius sp. CB (cross band type) is an amphidromous freshwater goby which receives paternal nest care under stones on river beds. This goby is known to migrate to the upper reaches of rivers as it grows. In the present study, the relationships among male mating success of Rhinogobius sp. CB, male body size, the size frequency distribution of river bed stones and the presence of the sympatric goby Tridentigerbrevispinis (which uses nest sites similar to those of Rhinogobius sp. CB) were investigated along the course of the Aizu River, Wakayama Prefecture, Japan. In the lower reach, where T.brevispinis was present and large stones were scarce, the sizes of the nest stones and the egg clusters of male Rhinogobius sp. CB were smaller than those of T.brevispinis. In the middle and the upper reaches, where T.brevispinis was absent and large stones were abundant, males of Rhinogobius sp. CB used larger nest stones than in the lower reach. In both gobies, there were positive correlations among male body size, nest size and egg cluster size in all reaches. Nest‐choice experiments carried out in the laboratory, with or without a rival, showed that males of both gobies preferentially used large nest sites and that large males had an advantage in male‐male competition for large nest sites. These results indicate that large male body size can increase male mating success and that male mating success increases in the upper reach in this goby. The migration pattern of Rhinogobius sp. CB was also discussed in relation to these findings.