Behavioral Ecology and Sociobiology

, Volume 48, Issue 3, pp 211–217

Sexual selection on mature male parr of masu salmon (Oncorhynchus masou): does sneaking behavior favor small body size and less-developed sexual characters?

  • Y. Koseki
  • K. Maekawa
Original Article

DOI: 10.1007/s002650000231

Cite this article as:
Koseki, Y. & Maekawa, K. Behav Ecol Sociobiol (2000) 48: 211. doi:10.1007/s002650000231


In many salmonid species, males exhibit morphological dimorphism associated with alternative mating behaviors. ”Precocious males” have a small body size with little or no development of sexual characters and adopt sneaking to gain access to females, while ”migratory males” of large body size and well-developed secondary sexual characters fight. We quantified selection on precocious male parr of masu salmon (Oncorhynchus masou) under simulated natural conditions to examine the contribution of morphology to sneaking success. In contrast to the prediction that sneaking behavior favors small body size, we detected selection favoring relatively large body size for sneaking success. This selection pressure was caused by the dominance hierarchy within parr and may have been facilitated by indifference of dominant migratory males to parr. Unlike the secondary sexual characters exhibited by migratory male salmon, such as the hooked snout and humped back, no morphological characters other than body size contributed to the reproductive success of masu salmon parr. This non-contribution may have been responsible for the lack of development of sexual characters in precocious males.

Key words Alternative mating behavior Morphological dimorphism Sexual selection Mature male parr Oncorhynchus masou 

Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • Y. Koseki
    • 1
  • K. Maekawa
    • 1
  1. 1.Laboratory of Conservation Biology, University Forests, Hokkaido University, N9 W9, Sapporo 060-0809, Japan e-mail:; Tel. +81-11-706-3655; Fax +81-11-706-3450JP