Factors Influencing the Breeding Activity in Male Masu Salmon, Oncorhynchus masou: The Relationship with Body Size |
| |
Authors: | Toshiaki Yamamoto Kaneaki Edo |
| |
Institution: | (1) Laboratory of Conservation Biology, Field Science Center for Northern Biosphere, Hokkaido University, 060-0809 Sapporo, Japan;(2) Graduate School of Environmental Earth Science, Hokkaido University, 060-0810 Sapporo, Japan;(3) Present address: Department of Veterinary Nursing and Technology, Nippon Veterinary and Animal Science University, 180-8602 Musashino, Japan |
| |
Abstract: | Synopsis Male body size has been emphasized as an important factor contributing to the breeding success of individuals. However, the
operational sex ratio (OSR: ratio of mature females to males) during the breeding season significantly change due to differences
in the breeding timing and period within and between males and females and may influence the selective advantage of the male
large body size for mates. We examined the reproductive ecology of masu salmon Oncorhynchus masou, inhabiting Lake Toya, Hokkaido, northern Japan. Precipitation triggered the upstream migration, although males migrated
into the river earlier than females. As a result, the OSR in the river changed markedly during the breeding season, as did
the size structure of males in the river. Large males migrated into the river earlier than the smaller males. Differential
male survival resulted in the different population size structure between the early and late periods. Under these conditions,
we analyzed which males were more successful in releasing the more sperm throughout the breeding season by estimating the
decrease in the sperm content in male carcasses. The body size and sperm-releasing success of the males were not related.
With a weak male-biased OSR and synchronous timing of reproduction in females, males that had entered the river succeeded
in releasing the sperm regardless of body size. Such a fluctuating advantage for different body sizes likely contributes to
the maintenance of the size variation in the male salmon. |
| |
Keywords: | OSR size structure sperm-releasing success reproduction salmon |
本文献已被 SpringerLink 等数据库收录! |
|