EVOLUTION OF BOTH-WAYS SEX CHANGE AND SOCIAL SYSTEMS AMONG FISHES

进一步分析了单配型虾虎鱼的双向性变资料，本文认为，群体间迁移所引起的社会地位的变化是双向性变进化的主要因素，这是在某些植物和海洋无脊椎动物中已知的双向性变进化的另外两个条件之外新发现的条件。群体运动也可能发生在一些其他的雄性先熟或雌性先熟的鱼类中，这些鱼类的性别变化是受社会控制的，并且在这些物种中有反向性别变化的可能性。本研究对三种雄性先熟、一夫一妻制的淡水白鲳进行了野外观察和饲养两条同性鱼的水族箱试验在3种先雌后雌和一夫多妻的海葵中，黑尾海葵不变性为雌，而在克氏双锯鱼、系带海葵和多角海葵中，雌性海葵不变性为雄，雌性海葵不变性为雌，但在雀鲷Dascyllus aruanus和濑鱼Labroides dimidiatus中，雄性将其泌尿生殖乳头的形状改变为雌性，尽管它们的生殖乳头的形状与雌性相似，但它们的生殖乳头的形状与雌性相似。根据这些结果，除了雌性向雄性的性别转换在所有已知的具有两种性别转换能力的鱼类中普遍存在外，还表明雄性先熟的进化因素可能抑制了反向性别转换的发生，这一预测有待进一步研究。

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.