Pre-oviposition Ejaculation as Mating Tactics of Sneaker and Fertilization
Sucessin the Rose Bitterling, Rhodeus ocellatus
Yoshihiko
Kanoh (1991) Bull. Seifu Gakuen@Vol. 6: 69-102
Department of biology, Seifu
High School , Osaka Japan
Abstract
The males of the rose bitterling which spawn into the
freshwater mussels form a territory around the mussel . But , because all males
can not occupy the territory , socially inferior small males take part in mating
by sneaking. Spawning into the mussel offers an advantage to sneakers , because
they intrude and release sperm not only after but also before egg laying . I
termed this ejaculating behaviour before egg laying 'pre-oviposition
ejaculation' . In the present study through analysis of isozyme I found the
effect of pre-oviposition ejaculation and the fertilization success of sneakers
under natural conditions . It is evident that pre-oviposition ejaculation is
effective for at least I minute before egg laying in the tank . Further I
estimate that in one breeding season under natural conditions the appearance
rate of sneaking tactics is 38. 4% and that the fertilization success obtained
by sneakers is 38. 2%. Such a correspondence between the appearance rate and the
fertilization success of two mating tactics (i.e. territorial male and sneaker)
implies that mating tactics of two types are selected by synchronical frequency
dependence . Consequently a dominance hierarchy which depends on body size
exerts an important influence on the social organization of the rose bitterling
, but it is not concerned with reproductive success .