| Cyanobacteria are the most important taxa causing harmful algal blooms(HABs)in freshwater ecosystems,and cyanobacterial blooms are thought to be increasing in intensity and frequency as a consequence of the combined effects of eutrophication,global warming,and exotic species invasion.Cladocera zooplankton is a critical position in the food chain,linking higher trophic organisms with producers.Cyanobacteria restrain the gro,wth and reproduction of Cladocera from its lacking nutritin,toxin and aggregated colonies.On the one hand,some species of Cladocera can eat cyanobacteria to suppress the over-expansion of cyanobacteria in the long-term survival environment of cyanobacteria.Indicating that Cladocera can resist the effects of cyanobacterial toxins and predators can defuse their prey to some extent.Defensive behavior,and predator attacks can manifest themselves through rapid adaptation.In this study,we used freshwater Cladoceran zooplankton as expeirmental organisms,with Daphnia magan,a kind of large Cladocerans.Microcystis aeruginosa was selected as the main cyanobacteria.We focused on the scientific issue of the "filter feeder zooplankton tolerant development of toxic cyanobacteria",and explored the response of large scorpion generations to the stress of M.aeruginosa.The results of this study mainly include the following five aspects.1.The response of the offspring to toxic M.aeruginosa when parental D.magan came from different waterThe 30 strains of D.magna isolated from 3 different waters from Ningxia,and the resistance of their progeny to tolerance to toxic M.aeruginosa was tested.The offspring of parents from different water had different fitness to toxic M.aeruginosa when feeding 100%Scenedesmus acuminatus and mixed algae(20%non-toxic M.aeruginosa +80%S.acuminatus).The suitability of the progeny of the parents of different water sources to toxic M.aeruginosa was significantly different,which showed that the growth rate of the progeny,the resistance to toxic M.aeruginosa in the different waters of the parent and the different clones in the same waters were significantly different.The results show that the ability of the offspring to tolerate the stress of M.aeruginosa between the different sources of water,which is the basis for the D.magna to adapt to the cyanobacteria stress.2.The response of the offspring which the parental D.magan grazing different M.aeruginosa to toxic M.aeruginosaThe 3 clones of D.magna was selected as parental,they were feeded by 3 food processing groups including S.acuminatus,non-toxic M.aeruginosa mixed food(non-toxic M.aeruginosa + S.acuminatus),toxic M.aeruginosa mixed food(toxic M.aeruginosa + S.acuminatus),raised for 4 generations.The second instar offspring of the fourth generation was feeded by toxic M.aeruginosa mixed food in order to test the resistance to toxic M.aeruginosa.The results showed that the offspring first reproductive time,reproductive capacity have significantly increased after the parental grazing food containing non-toxic or toxic M.aeruginosa,and there was a significant difference between offspring of non-toxic and toxic M.aeruginosa to the improvement of this resistance in the parental experience.3.The response of the offspring to toxic M.aeruginosa when the parental D.magan was forced by non-toxic M.aeruginosa for the whole generationThe parental D.magan was feeded by non-toxic M.aeruginosa mixed food(20%non-toxic M.aeruginosa +80%S.acuminatus)for more than three months,each instar of their offsprings was test by toxic M.aeruginosa.It was found that the progeny of the parent generation at the sixteenth instar to the twentieth was more tolerant to toxic M.aeruginosa than the offspring produced at the age of I to the age of?.It showed that with the prolongation of the parental cyanobacteria stress time,its progeny have increased ability to adapt to microcystis stress.4.The response of the offspring to toxic M.aeruginosa when the parental D.magan was forced by non-toxic Microcystis for three generationsThe parental Daphnia magan was feeded by non-toxic M.aeruginosa mixed food(20%non-toxic M.aeruginosa+80%S.acuminatus)for three generations,the resistance of offsprings was test by toxic M.aeruginosa in every generations.The results showed that the life history characteristics and the moderation of offspring in M.aeruginosa were higher than those in the normal diet group.But the offspring's fitness increased from the first,second generation to the third generation.This suggested that the increased tolerance to toxic M.aeruginosa was the development of the defense induced during the individual's life history,this property can be passed from the mother to the offspring and was not directly affected by the grandparents.5.The fitness of the offspring to toxic M.aeruginosa when the parental D.magan was forced by non-toxic M.aeruginosa for long generationsThe parental D.magan was feeded by non-toxic M.aeruginosa mixed food(20%non-toxic M.aeruginosa +80%S.acuminatus),for long generations(10 generations),to investigate the effects of successive generations of large parental progeny on Microcystis aeruginosa,the response of progeny to toxic M.aeruginosa,and the effect of diet recovery on the tolerance of progeny to M.aeruginosa.The results showed that the growth and reproduction of leeches were severely affected by M.aeruginosa.The survival rate(lx),reproduction rate(mx),and larval growth rate(Gj)were far lower than those of the normal culture group.After 10 consecutive Cyanobacteria generations,the growth rate of offspring slowed and the reproduction rate increased significantly.It showed that leeches have been exposed to M.aeruginosa for several generations in a row,and their tolerance to M.aeruginosa has developed,and this tolerance may be related to the time and manner of action of toxic cyanobacteria.When the parent is restored to normal bait,the large fleas of the progeny still possess the characteristics of adapting to the toxic microcystis,but this adaptive performance will gradually decrease with the increase of the recovery generation. |
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