桡足类滞育规律研究

Preliminary studies on the rule of copepod diapause

首次提出用滞育指数对桡足类滞育能力进行相对量化处理 ,并对 10 2种桡足类的滞育能力同迁移能力、体长、栖息地之间的关系进行了数学分析 ,初步得出了滞育在桡足类中的分布规律 :在桡足类中滞育与迁移呈负相关 ,两者之间存在一定程度的置换 ;个体较小的桡足类一般具有较强的滞育能力和较弱的迁移能力 ,个体较大的桡足类一般具有较弱的滞育能力和较强的迁移能力 ;淡水桡足类一般比海洋桡足类具有较强的滞育能力。

Many copepods have integrated a state of diapause in their life history to avoid the critical conditions. It has been showed that the diapause trait is by no means evenly distributed within copepods, such as different diapausing forms (Diapause occurs in eggs, copepidites or adults.) and different diapausing locations (in water column or in sediment). In this paper we attempt to investigate the distribution of diapause among copepods based on the published data of 102 species from 3 orders of pelagic copepods. The index of diapause and the index of migration are adopted in order to mathematically analyze. The index of diapause is described as follow: (1)lowest diapause,species diapausing with the form of copepidites or adults in the water column; (2)moderate diapause,species diapausing with the form of copepidites or adults in the sediment; (3)highest diapause,species diapausing with the form of eggs in the sediment. The index of migration is ranked as follow: (1)lowest migration,pond and lake dwelling species; (2)moderate migration,species living in the coastal areas; (3)highest migration,species living in the open sea. The relationship between the index of diapause and the index of migration is highly negatively significant (R^2=0.3932, (P0.00001,) n=102).It suggests that there is a highly negative relationship and a trade-off between the diapause ability and the migratory ability among copepods. The relationship between the index of migration and the body length is highly positively significant (R^2=0.3220, P0.00001, n=102). And the index of diapause negatively covaries with the body length (R^2=0.1871, P<0.00001, n=102).The results show that strong diapause and weak migration are more common among small copepods, whereas large species have weak diapause and strong migration. The index of diapause of freshwater copepods is higher 25.3% than that of marine copepods. It suggests that species with prolonged diapause tend to be found in inland water. Two possible explanations for those uneven distribution of diapause are discussed. The one is microevoluntionary. The patterns reflect selection pressure exerted on copepods by the environment in which they live:diapause is favored in some habitats and not in others. Another explanation is macroevoluntionary. The patterns are the result of phylogenetic history:if the ancestors of some taxa did not evolve diapause, their descendants may also lack the trait whatever the selection pressure may have been.