温度和食物浓度对大型溞Daphnia magna种群动态和两性生殖的影响

Effect of temperature and food concentration on population dynamic and sexual reproduction of Daphnia magna

在4个温度（15、20、25、30℃）和3个食物浓度（1×10^4,1×10^5,5×10^5cells ml-1）下研究了大型溞（Daphnia magna）淮河种群的动态和两性生殖,结果表明：（1）在实验初期,大型溞种群密度不断增加,达到最大值后种群密度呈现缓慢下降或趋于稳定的趋势。除15℃下最大瞬时增长率（1.36 d^-1）出现在中食物浓度组外,20℃（1.51 d^-1）、25℃（1.39 d^-1）、30℃（0.69 d^-1）下的最大瞬时增长率均出现在高食物浓度组。（2）相同温度下,食物浓度与大型溞最大种群密度间存在显著正相关（p〈0.01）。（3）相同食物浓度下,随温度升高,大型溞首次产幼溞时间（5～21d）和到达最大种群密度的时间（15～29d）缩短,首次抱卵时的体长（1.75～2.67 mm）减少。（4）在较低的温度和中食物浓度组下,大型溞产生了较多的休眠卵或卵鞍（15℃：（16.7±2.5）ind.和20℃：（18.3±3.8）ind.）;30℃下没有出现休眠卵或卵鞍。除15℃、中食物浓度组外,其它实验组均产生雄体。实验25d后,雄体密度与种群密度呈显著的相关性（30℃：p〈0.05;15～25℃：p〈0.01）。（5）本研究结果暗示大型溞休眠卵的形成受温度、食物浓度和种群密度的共同影响,且较低的温度是大型溞休眠卵形成的主要诱因。

Population dynamics and gamogenesis of Daphnia magna from Huaihe River were studied under four temperatures （ 15, 20, 25, 30℃ ） and three food concentrations （ 1 × 10^4, 1 × 10^5, 5 ×10^5cells ml^-1 ）. During early days of experiment, population density of D. magna increased continuously, and it presented a trend of decrease or stabilization after it reaebed the density peak. Maximal instantaneous increase rate occurred at 15℃ under middle food concentration （ 1.36 d^-1 ）, while appeared at other temperatures under high food level （20℃ ： 1.51 d^-1 ; 25℃ ： 1.39 d^-1 ; 30℃ ： 0. 69 d^-1 ）. At same temperature, the maximal population density （MPD） of D. magna were significantly positively correlated with food concentrations （p 〈0.01 ）. At same food concentration, first brood time （5 --21 d）, the time reaching MPD （15 --29 d） and the body length of D. magna at first reproduction （1.75 -2.67 mm） decreased with increasing temperature. The more resting eggs were observed in the combinations of middle food concentration and low temperatures （ 15℃ ： （ 16.7 ± 2.5） ind. ; 20℃ ： （ 18.3 ± 3.8） ind. ）. No resting eggs/ephippia occurred at 30℃. Males occurred in all combinations except the combination of 15℃ and middle food level. Male density and population density of D. magna were significantly positively correlated 25 days after the beginning of the experiment （30℃ ： p 〈 0.05; 15 --25℃ ： p 〈 0.01 ）. Our results suggested that the formation of resting egg/ephippium and male of D. magna was affected by temperature, food level and population density, and lower temperature was main inducement.