利用种群增长研究镜湖夏季萼花臂尾轮虫对水温的适应

ADAPTATION OF BRACHIONUS CALYCIFLORUS (ROTIFERA) FROM LAKE JINGHU IN SUMMER TO WATER TEMPERATURE:POPULATION GROWTH EXPERIMENT STUDY

运用种群增长实验方法,在4个温度(20℃、24℃、28℃和32℃)和3个斜生栅藻[Scenedesmus obliquus(Turpin)Kuetzing]密度(1.0×106、2.0×106和4.0×106 cells/mL)共12个条件组合下研究了镜湖夏季出现的萼花臂尾轮虫(Brachionus calyciflorus Pallas)的种群增长率、平均混交率、平均受精率和休眠卵产量等生殖参数。结果表明,在各食物密度下,轮虫种群增长率均在28℃和32℃下最高。平均混交率、平均受精率和休眠卵产量等与温度间的关系因食物密度的不同而异。温度对种群增长率、平均混交率、平均受精率和休眠卵产量均有极显著性影响(P<0.01),食物密度对种群增长率和休眠卵产量均有极显著性影响(P<0.01),温度和食物密度的交互作用对平均混交率、平均受精率和休眠卵产量均有极显著性影响(P<0.01)。在1.0×106、2.0×106和4.0×106 cells/mL的斜生栅藻密度以及28℃和32℃下,轮虫具有较高的种群增长率(1.50—1.95/d)表明该种群能够适应较高的水温,水温不是导致其在夏季水体中具有极低的种群密度(远低于1个/L)的直接因素。在种群存在于镜湖水体期间(7月初至12月初),特别是当水温降至20℃左右时,其较高的休眠卵产量为该种群在次年的同一时段在水体中重新出现提供了保证。

To study the population growth rate, average proportion of mictic females, average fertilization rate of mictic females, and resting egg production, Brachionus calyciflorus collected from Lake Jinghu were investigated at four tem-peratures (20℃, 24℃, 28℃and 32℃) and three Scenedesmus obliquus densities (1.0×106, 2.0×106 and 4.0×106 cells/mL) by population growth experiments. The results showed that the population growth rate of B. calyciflorus at 28℃ and 32℃ was the highest at all three food levels. At 1.0×106 cells/mL of S. obliquus, the average proportion of mictic fe-males at both 20℃ and 24℃ was significantly lower than that at 32℃, but it was not markedly different compared to that at 28℃. The average fertilization rate of mictic females at both 24℃and 28℃was the highest, and it was the low-est at 32℃. At 2.0×106 cells/mL of S. obliquus, the average proportion of mictic females at 20℃ was the highest. The average proportion of mictic females at 24℃was lower than that at 32℃, but it was not significantly different compared to that at 28℃. The average fertilization rate of mictic females at 20℃, 24℃and 28℃was all higher than that at 32℃. The resting egg production at 20℃ was the biggest. At 4.0×106 cells/mL of S. obliquus, both the average proportion of mictic females and the resting egg production at 20℃ were higher than those at any other temperatures. The average fertilization rate of mictic females at both 20℃ and 24℃ was the highest, and it was the lowest at 32℃. Two-way ANOVA analysis indicated that temperature significantly affected population growth rate, average proportion of mictic females, average fertilization rate of mictic females, and resting egg production (P<0.01), food level affected population growth rate and resting egg production (P<0.01), and temperature and food level cooperatively affected average propor-tion of mictic females and average fertilization rate of mictic females, and resting egg production (P<0.01). These re-sults indicated that the rotifer population adapts high water temperature and water temperature does not directly account for the very low population density of B. calyciflorus in Lake Jinghu in summer, and that the high resting egg production of B. calyciflorus at low temperature may contribute to its reoccurrence in Lake Jinghu during the same period of next year.