Sperm allocation pattern during a reproductive season in the copulating marine cottoid species, <Emphasis Type="Italic">Alcichthys alcicornis</Emphasis> |
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Authors: | Hiroyuki Munehara Hiroshi Murahana |
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Institution: | (1) Usujiri Fisheries Station, Field Science Center for Northern Biosphere, Hokkaido University, Usujiri 152, Hakodate, 041-1613 Hokkaido, Japan |
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Abstract: | The sperm allocation pattern of a copulating marine cottid fish, Alcichthys alcicornis, was investigated. A total of 86 mating events using six males were conducted in aquarium tanks over 10 days, and in 36 of
them, spermatozoa were collected using a false copulation method. Males released 3–8 × 108 spermatozoa in early events, with the number decreasing gradually during subsequent mating events. This sperm allocation
was represented as an “early investment and tapering” pattern. It was discussed why males have significantly higher sperm
release in early spawning events. The reproductive behavior consists of spawning and subsequent copulation. Spermatozoa have
the ability to fertilize eggs from multiple clutches, and in earlier produced clutches the level of sperm competition should
be relatively low. In addition, if early spawn happens to be the first spawn with a female, spermatozoa that are released
into the water column after spawning are responsible for fertilizing the female’s first clutch. The probability of this occurring
should decrease dramatically as the season progresses, due to the highly synchronous seasonal spawning of females. All of
these factors should select for high sperm numbers in early ejaculates. Based on such reproductive ecology of A. alcicornis we hypothesize that this sperm allocation pattern is an adaptive reproductive strategy in response to egg availability and
sperm competition occurring within the ovarian cavity. |
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