title: Sperm allocation in relation to female size in a semelparous salmonid.
abstract: To maximize reproductive success, males have to adaptively tailor their sperm expenditure in relation to the quality of potential mates because they require time to replenish their sperm supply for subsequent mating opportunities. Therefore, in mating contexts where males must choose among females in a short period of time, as is the case with semelparous species (which die after one intensely competitive short duration breeding season), selection on sperm allocation can be expected to be a powerful selective agent that shapes the male reproductive success. We quantitatively investigated sperm allocation patterns in chum salmon in relation to perceived female quality by developing a novel method for determining the amount of sperm allocated per ejaculate during spawning bouts. We examined the relationship between sperm expenditure and the body size of paired females (a proxy of egg number and egg quality) in the absence of male-male competition in an experimental channel. The estimated amount of sperm released per spawning event was positively correlated with the size of paired females. However, the number of spawning events a female participated in, which reduces the number of eggs she spawns in each subsequent bout, did not affect this relationship. These results provide support for predictions arising from the sperm allocation hypothesis, male salmon do economize their sperm expenditure in accordance with paired female body size as predicted for their first spawning event, but males overestimate or are unable to assess the quality of females beyond size and provide more sperm than they should in theory when paired with a female that spawned previously. Overall, the observed sperm allocation pattern in chum salmon appears to be adapted to maximize reproductive success assuming female size is an honest indicator of quality, although temporal changes in a female's quality during a reproductive season should be considered when examining sperm allocation strategies.
authors.affiliation: College of Bioresource Sciences , Nihon University , 1866 Kameino, Fujisawa, Kanagawa 252-0880 , Japan.
authors.forename: Yuya
authors.identifier: 0000-0001-8148-9394
authors.initials: Y
authors.lastname: Makiguchi
authors.affiliation: Shibetsu Salmon Museum , Shibetsu, Hokkaido 086-1631 , Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Ichimura
authors.affiliation: College of Bioresource Sciences , Nihon University , 1866 Kameino, Fujisawa, Kanagawa 252-0880 , Japan.
authors.forename: Takenori
authors.initials: T
authors.lastname: Kitayama
authors.affiliation: Institute for East China Sea Research , Nagasaki University , Nagasaki 851-2213 , Japan.
authors.forename: Yuuki
authors.initials: Y
authors.lastname: Kawabata
authors.affiliation: Atmosphere and Ocean Research Institute , The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564 , Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kitagawa
authors.affiliation: College of Bioresource Sciences , Nihon University , 1866 Kameino, Fujisawa, Kanagawa 252-0880 , Japan.
authors.forename: Takahito
authors.initials: T
authors.lastname: Kojima
authors.affiliation: Department of Biological Sciences, University of Windsor, Windsor, Ontario, CanadaN9B 3P4; Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario, CanadaN9B 3P4.
authors.forename: Trevor E
authors.initials: TE
authors.lastname: Pitcher
keywords: acceleration data loggers; female body size; mate choice; spawning behaviour