Sexual selection on mature male parr of masu salmon (Oncorhynchus masou): does sneaking behavior favor small body size and less-developed sexual characters? |
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Authors: | Y Koseki K Maekawa |
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Institution: | (1) Laboratory of Conservation Biology, University Forests, Hokkaido University, N9 W9, Sapporo 060-0809, Japan e-mail: koseki@exfor.agr.hokudai.ac.jp; Tel. +81-11-706-3655; Fax +81-11-706-3450, JP |
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Abstract: | 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.
Received: 15 November 1999 / Accepted: 20 May 2000 |
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Keywords: | Alternative mating behavior Morphological dimorphism Sexual selection Mature male parr Oncorhynchus masou |
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