温度和种间竞争对大型溞种群动态和两性生殖的影响

在20℃、25℃下,将大型溞和老年低额溞分别按7+3(B组),5+5(C组),3+7(D组)的组合进行混合培养,以及用单种培养(10+0(A组),0+10(E组))作为对照,研究了温度和种间竞争对大型溞种群动态和两性生殖的影响.实验结果表明:在混合培养时,大型溞对老年低额溞产生明显的竞争优势.20℃、25℃下,单种培养的老年低额溞最大种群密度分别为大型溞的2.31和1.97,而在混合培养下老年低额溞的种群密度明显低于大型溞,在实验25d后几乎全部死亡.25℃下两种溞的种群密度之间存在极显著的负相关性(C组:r=-0.508,n=30,P<0.01;D组:r=-0.483,n=30,P<0.01).在20℃、单种培养下,大型溞在首次产幼溞时即出现雄体,且种群密度与雄体密度呈显著的相关性(r=0.678,n=24,P<0.01).大型溞的最大雄体密度(106 ind.(200ml)~(-1))和最大雄体比例(36.8%)均出现在20℃、单种培养下.25℃下,大型溞在混合培养的B组和C组首次产幼溞时即出现雄体,且雄体在混合培养B组的比例达28.2%.大型溞在25℃、单种培养下没有产生卵鞍,在混合培养下总计产生66个卵鞍,其中空卵鞍占51.5%,而在20℃、混合培养下没有卵鞍产生.实验结果暗示:在较高的温度下,种间竞争刺激了大型溞雄体的产生和卵鞍的形成,高密度的雄体有助于大型溞孤雌生殖雌体向两性生殖雌体的转化.

Effect of temperature and interspecific competition on populaiton dynamics and sexual reproduction of Daphnia magna

Under isolated and mixed cultures of Daphnia magna and Simocephalus vetulus, the effect of temperature and interspeific competition on populaiton dynamics and sexual reproduction of D. magna was investigated. The mixed cultures included three density combinations: A, 7D+3S;B, 5D+5S;C, 3D+7S. The results showed D. magna had a competitive advantage over S. vetulus under all mixed cultures. At 20℃ and 25℃, maximal population densities of S. vetulus were 2.31 and 1.97 times than one of D. magna under isolated cultures, respectively. But population density of S. vetulus was much lower than one of D. magna under mixed cultures, and S. vetulus died away after twenty-five days. Negative relationships between the population densities of D. magna and S. vetulus were significant (C: r=-0.508, n=30, P<0.01;D: r=-0.483, n=30, P<0.01). Males of D. magna occurred in all density combinations during the experiment. The population density of D. magna was positively correlated with its male density (r=0.678, n=24, P<0.01) under 20℃ and isolated cultures, and males of D. magna were induced at first reproducion. Maximal male density (106 ind.(200ml)~(-1)) and maximal male percentage (36.8%) appeared under 20℃ and isolated culture. The males of D. magna appeared at first reproduction in B and C combinations at 25℃, and the proportions reached 28.2% in B combinations.No ephippia were produced by D. magna under isolated culutres at 25℃ and mixed cultures 20℃, while there were 66 ephippia under mixed cultures at 25℃, among which 51.5% was empty. The results indicated that the interspecific competition induced the production of males and the formation of ephippia in D. magna, and high density of males might promote to switch from parthenogenic females to sexual females in D. magna.