- 著者
- Haruko Yoshie Yoichi Yusa
- 出版者
- JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY
- 雑誌
- Applied Entomology and Zoology (ISSN:00036862)
- 巻号頁・発行日
- vol.43, no.4, pp.475-482, 2008-11-25 (Released:2008-11-30)
- 参考文献数
- 24
- 被引用文献数
- 21 23
We studied the predatory potential of the turtle Chinemys reevesii on the apple snail Pomacea canaliculata using two series of experiments. First, we investigated the relationship between turtle body size and the maximum size of snails consumed over a period of 3 days within 0.37 m2 containers. The maximum snail size consumed was positively related with turtle size. Secondly, we investigated the predation of snails by turtles over a period of 8 weeks. We released 200 snails (10–30 mm shell height) and an adult turtle (155–183 mm carapace length) into each of two 2.08 m2 plots with soil and rice plants. Subsequently, snail density was monitored every week and 200 snails were added to low density plots up to twice a week. Two control plots with the same initial density of snails but without turtles were also monitored. The density and survival rate of snails were lower in plots with a turtle than in control plots. We estimated that a single turtle consumed >2,000 snails in 8 weeks. In addition, the biomass of duckweed (given as food for snails) was greater in turtle plots than in control plots, suggesting that the presence of turtles had an indirect effect on weed.
- 著者
- Noriko Yasuoka Yoichi Yusa
- 出版者
- 日本プランクトン学会、日本ベントス学会
- 雑誌
- Plankton and Benthos Research (ISSN:18808247)
- 巻号頁・発行日
- vol.12, no.1, pp.78-81, 2017-02-28 (Released:2017-02-28)
- 参考文献数
- 27
- 被引用文献数
- 2
Two Saccostrea oysters (S. glomerata and S. cucullata) are considered to be protandric hermaphrodites based on indirect observations. However, no other information is available on the sexual systems of Saccostrea oysters and the potential for bi-directional sex change has not previously been reported in them. Therefore, the present study was undertaken to investigate the sexual systems of S. kegaki and S. mordax in western Japan, utilizing field sampling and in situ experiments. In the field sampling, shell length (SL) and sex were determined during the reproductive season of these oysters (June–October) in 2012. Then, sex change was directly observed between 2013 and 2016 by determining the sex of individuals through gonadal biopsy, re-attaching the individuals in the field, collecting the survivors in the following year, and determining their sex by dissection. In both species, the proportion of males decreased with increasing SL, although the SL of males and females greatly overlapped. Direct observations showed that both male-to-female and female-to-male sex change occurred. Thus, our results indicated that both Saccostrea species tend to be protandric, but have the ability to change sex in both directions under natural conditions.