【摘要】 <正> 孤雌生殖与两性生殖的交替是枝角类对外界环境条件的一种特殊适应。当环境条件良好时,孤雌生殖的雌体所产的夏卵,不需要受精就能迅速发育。可是,环境条件一旦恶化,孤雌生殖就逐渐被两性生殖所代替。这时,雌体产出的冬卵,必需受精才能发育。受更多还原

【Abstract】 An investigation on the seasonal variations in the reproductive capacity of freshwater Cladocera was made and samples of Moina irrasa Brehm and Daphnid pulex (De Geer) were collected at random from two ponds near our laboratory between April 1961 and March 1962. The length of each adult parthenogenetic female was measured. Either the eggs or the developing young were dissected from the brood pouch and were counted. The results obtained from the statistical analyses of the number of eggs or young per brood, the body length and sample regression coefficient are summarized as follows.1. The reproductive capacity of parthenogenetic female of Moina irrasa ranges from 1 to 50 eggs or young per brood, with an average of 10.35.2. The reproductive capacity of Dapknia pulex observed in the present study ranges from 4 to 82, averaging at 24.03. This number is larger than that reported by other investigators.3. There is a marked seasonal variation in the reproductive capacity of Moina, with two peaks in spring and two in autumn, the former being greater than the latter. Its minimum occurs in summer.4. Seasonal variations in the reproductive capacity of Daphnia show only one peak which occurs in spring. The animals die off early in mid-autumn.5. The reproductive capacity depends upon the size of the female. There is a general tendency of increase in number of eggs or young per brood with the increase in size of the female.6. Seasonal variations of the reproductive capacity seem to be controlled mostly by available food and water temperature.更多还原