| With lake eutrophication,the interaction between M.aeruginosa and Daphnia has been widely paid attention by researchers.Although there are many studies about the effects of single M.aeruginosa strain on the life-table of Daphnia species,the researches on the influence of different M.aeruginosa strains on the life-history traits and its plasticity of Daphnia species from different lakes are insufficient as well as different sedimentary age.In this study,D.similoides sinensis populations from different sedimentary layers of both Lake Chaohu in Anhui province and Lake Junshan in Jiangxi province were chosen as the experimental animals.Using the Scenedesmus obliquus and two M.aeruginosa strains as food,four food treatments(M0: 100% S.obliquus;M10: 90% S.obliquus+10% M.aeruginosa;M20: 80% S.obliquus+20% M.aeruginosa;M40: 60% S.obliquus+40% M.aeruginosa)were employed,and the effects of M.aeruginosa on the life-history characteristics and its plasticity of D.similoides sinensis were studied.Our goals are to explore the spatial and temporal differences in the adaptability of D.similoides sinensis to M.aeruginosa,in order to further reveal the ecological mechanism of the interaction between D.similoides sinensis and M.aeruginosa.Our results will provide a theoretical basis for the controlling of cyanobacterial blooms in eutrophic lakes.Main results are as follows:1.The influences of same M.aeruginosa strain on the life-history characteristics and its plasticity of D.similoides sinensis from same lake were studied as well as different sedimentary age.With the increase of M.aeruginosa concentration,the growth and reproduction parameters of D.similoides sinensis from two lakes were all inhibited as well as differentary age,and the effects of both sedimentary age and M.aeruginosa concentration on the growth and reproduction of D.similoides sinensis were all significant(P<0.05).The body length at maturity and maximum body length,somatic growth rate at juvenile and before 15 days,and number of eggs at first pregnancy and cumulative eggs number of 1 cm populations from Lake Chaohu in four food treatments were all significantly lower than those of 14 cm populations(P<0.001).Their minimum values appeared all in the M40 treatment.However,time to maturation,cumulative offspring numbers and generation time of 1 cm populations from Lake Chaohu are all significantly higher than those of 14 cm populations(P<0.05),and maximum time to maturation(234.2±33.5 h)occurred in the M40 treatment.Moreover,the lifespan and No.offspring at first reproduction and net reproduction rate of D.similoides sinensis had no significant differences between 1cm populations and 14 cm population.Several life-history parameters of D.similoides sinensis 1 cm populations from Lake Junshan were significantly larger than those of 26 cm populations(P<0.05).The lifespan of 26 cm populations from Lake Junshan in the food treatments containing M.aeruginosa(M10,M20,M40)were between 12.1±3.2d and 15.9±5.3 d.Compared with 1 cm populations from Lake Chaohu,net reproduction rate of 1 cm populations from Lake Junshan in the M10 treatment was low(5.90±3.48).Time to maturations of 26 cm population from Lake Junshan were significantly higher than those of 1 cm populations(P<0.001),and its maxmum value(106.2 ± 18.3 h)appeared in the M40 treatment.Consistent with the populations from Lake Chaohu,No.offspring at first reproduction of D.similoides sinensis between 1 cm and 26 cm populations from Lake Junshan had no significant difference,and almost no neonates were produced.2.The influences of different M.aeruginosa strains on the life-history characteristics and its plasticity of D.similoides sinensis from different lakes were studied as well as different sedimentary ages.Sediment(sedimentary ages),M.aeruginosa concentration and their combination had all significant effects on several growth and reproduction parameters of D.similoides sinensis(P<0.05).14 cm populations from Lake Chaohu were significantly larger than 1 cm populations interms of lifespan,cumulative offspring number and net reproduction rate in four food treatments(P<0.05),whereas the intrinsic rate of increase of 1 cm populations was higher than that of 14 cm populations.Time to maturations of both 1 cm and 14 cm populations from Lake Chaohu in the M0 treatment were obviously shorter than those in the food treatment containing M.aeruginosa(M10,M20 and M40),and the maximum(182.8±14.6 h)appeared in the M40 treatment of 1 cm population from Lake Chaohu.No.Offspring at first reproduction of D.similoides sinensis had no significant difference between 1 cm and 14 cm populations from Lake Chaohu.The body length at maturity,somatic growth rates at juvenile and before 15 days,and number of eggs at first pregnancy of 26 cm populations of D.similoides sinensis from Lake Junshan were significantly higher than those of 1 cm populations(P<0.001).Compared with the M0 treatment,time to maturation of 26 cm population from Lake Junshan was shorter than those in the treatments containing M.aeruginosa whereas it was prolonged for 1 cm populations,and the maximum(187.1±35.2 h)appeared in the M40 treatment of 1 cm population.In addition,higher net reproduction rates of 1 cm population from Lake Junshan in the M10 and M20treatments(M10: 131.88±51.67,M20: 21.74±12.03)were observed.In summary,M.aeruginosa have obvious negative effects on the life-history parameters of different D.similoides sinensis populations,and these negative effects are enhanced with the increase of M.aeruginosa concentrations.Moreover,the plasticity of the life-history parameters of D.similoides sinensis should be affected by different D.similoides sinensis populations and M.aeruginosa strains. |
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