溜池におけるドブガイの個体間距離及びその決定要因の推定  [in Japanese] Estimation of the Factors Determining the Intervals among Individuals of the Freshwater Mussel Anodonta woodiana Lea (Bivalvia : Unionidae) in a Small Pond  [in Japanese]

In order to analyze the factors determining the intra-individual distance among the freshwater mussel, Anodonta woodiana, the survey was carried out at a small pond (200 m^2) in Toyonaka City, Osaka Prefecture in March 1985. After draining the small pond, 32 quadrates (32 m^2) were set up on the bottom of the pond. And then, positions of the total 492 mussels were recorded. The sex ratio (♀/♂) was 1.33 and the incubatioin ratio in females was 61.3%. The short distance between two individuals were from 0 to 10 cm in many cases (75.4%, n=312). This fact shows that the mussels have the concentrated patchy distribution in the pond. Based on the distance among individuals, the mussels were divided into three groups, which were compared in terms of the sex ratio and the incubation ratio. Most of the males live in relatively short distance (less than 10 cm) between them, many females keep larger intervals in between (more than 10 cm), and their incubation ratio was high. Some females with eggs and larvae stay on in their groups, and others do not. In short, intra-interval distance among the mussels may depend on their breeding conditions.