| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1998: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1997: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1996: ¥800,000 (Direct Cost: ¥800,000)
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| Research Abstract |
Field and aquarium experiments were carried out on sexual difference and sex change in two labrid fishes, Halichoeres melanurus and Labroides dimidiatus, on Sesoko Island, Okinawa.
1. In H. melanurus, sexual differences were found not only in body size and color, but also in ventral and caudal fin length. Since males were territorial each other to defend spawning sites, body size was most effective on males' mating success. Females preferred large bright males than small drab ones.
2. When males were removed from their territories, the largest females changed sex. Sexual behavior changed first, then gonad, and lastly body color changed.
3. After male loss, females chose the largest female as their mate, and female-female spawning often occurred releasing eggs without fertilization. The largest female performed complete male behavior, but could spawn as female when the male was returned soon.
4. Also in L. dimidiatus that had no sexual difference in body color, the largest female spawned with smaller females in male role when their male was removed. The largest females in both species should take male role as soon as possible to keep their mates until completion of gonadal sex change.
5. It is suggested that mate choice mechanisms may affect not only on the evolution of sexual difference but also on the process of sex change.
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