| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1994: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1993: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
The further analysis of our data on both-ways sex change in the monogamous gobies, Paragobiodon and Gobiodon, suggested that the change of social status as the result of movement between groups was the main factor for the evolution of their both-ways sex change.This is the newly found condition in addition to the other two conditions for the evolution of both-ways sex change known in some plants and marine invertebrates.The inter-group movement may occur also in some other protandrous or protogynous fishes, in which sex change is socially controlled, and the possibility of sex change in the reverse direction is suggested in such species.
To confirm whether they could change sex in the reverse direction, I carried out the field obervations and the aquarium experiments of keeping two fish of the same sex.In three protandrous and monogamous species of the anemonefishes, Amphiprion clarkii, A.frenatus and A.perideraion, the females were aggressive each other and never changed sex to male to form a new pair.Out of three protogynous and polygynous species, the males never changed sex to female in the wrasse Halichoeres melanurus, but in the damselfish Dascyllus aruanus and the wrasse Labroides dimidiatus the males changed the shape of their urogenital papillae to that of females although their breeding as females has not yet been observed.
From these results in addition to the fact that female to male sex change is prevailing in all the fishes that are known to have abilities to change sex in both ways, it is suggested that the factors for evolution of protandry may inhibit the occurrence of sex change in the reverse direction.This prediction will be further investigated.
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