Pre-oviposition Ejaculation in Externally fertilizing Fish: How Sneaker Male
Rose Bitterlings Contrive to Mate
YOSHIHIKO KANOH (1996)
Ethology 102: 883-899（ＰＤＦ）
Department
of Biology, Osaka Kyoiku University, Asahigaoka, Kashiwara-shi, Osaka
Synopsis
Pre-oviposition ejaculation as a mating tactic of sneaker males
in the rose bitterling, Rhodeus ocellatus, was studied under natural and
artificial conditions. In a small pond in Yao city, Osaka, Japan, the
operational sex ratio of males and females was found to be approximately 3.5:1
and the proportion of males to the mussels, which serve as spawning beds for the
rose bitterling, was approximately 2:1. Competitively subordinate rose
bitterling males which spawned into the mussels participated in mating by
sneaking, because not all males could occupy territories around the mussels. The
sneaker males often released sperm not only after but also before egg-laying
(this ejaculation movement by the male before egg-laying is termed
'pre-oviposition ejaculation'). In pair spawning with sneaker, the sneakers
frequently performed pre-oviposition ejaculations, which territorial males never
performed. In the field, pre-oviposition ejaculations by sneakers coincided with
the leading of females by territorial males. Under artificial conditions, I
demonstrated by using electrophoretic paternal analyses that the pre-oviposition
ejaculations by the sneakers were more effective than the post-oviposition
ejaculations by the territorial males. In addition, there were negative
size-dependences in ejaculation achievement rate and fertilization success of
the sneaker males.
Yoshihiko KANOH, Section of Biology, Seifu High School,
12-16 Ishigatsuji-cho, Tennohji-ku, Osaka, 543 Japan.