Effects Of Algal Food Concentration On The Growth And Reproduction Of Four Common Tropical Cladoceran Species

Diaphanosoma excisum and Diaphanosoma dubium are common small and medium body-sized cladocerans in fresh waters,while Daphnia similoides and Daphnia galeata are large body-sized cladocerans,all the four species distribute in lakes and reservoirs in subtropical areas,but their competition and adaptation for tropical reservoir are not yet be understood,and there is few information of their life history except of D.dubium.In order to know the effects of algal food concentration and temperature on the growth and reproduction of the four common species in Cladocera,the experiments of life history were conducted with an independent device to cultivate each animal of the four species to record their growth and reproduction.Five concentrations of chlorella pyrenoidosa was used to feed D.excisum and D.dubium(0.05,0.1,0.2,0.3,1.0 mg C·L^–1)at 20?and(0.2,0.3,0.4,0.5,1.0 mg C·L^–1)at 30?,and(0.3,0.5,1.0,1.5,2.0 mg C·L^–1)for D.similoides and D.galeata at25?.According to the observation and records,we established a life table for each animal,and we calculated their individual growth speed,species breeding parameters,and determined their threshold food concentration?TFC?according to the growth rate.The results are summarized as follows:1.Under each temperature,the somatic growth rate,the intrinsic rate of increase,the size at maturity and the mean number of eggs per brood of D.excisum,D.dubium,D.similoides and D.galeata increased with the increasing organic carbon concentrations of Chlorella pyrenoidosa,whereas the duration of reproduction decreased.Food concentration was an important factor affecting the growth and reproduction of the four experimental species.High concentrations of food is more advantageous to the growth and reproduction of the four animals.2.Under each food concentration,the somatic growth rate,the intrinsic rate of increase,the size at maturity and the mean number of eggs per brood of D.excisum,D.dubium,D.similoides and D.galeata became higher at the high temperature?30??,and the duration of reproduction and average lifespan decreased.The temperature is also the important factor affecting the growth and reproduction of D.Excisum and D.Dubium.3.Under each temperature and food concentration,compared to D.dubium,D.excisum had the shorter duration of reproduction,the longer average lifespan,the larger size at maturity and the longer generation time,and the more cumulative eggs for each adult and the more eggs per brood,the higher net reproductive rate and higher intrinsic growth rate.It means that D.excisum was more competitive than D.dubium.Under the same temperature and food concentration,compared to D.galeata,D.similoides had a shorter duration of reproduction,a shorter average lifespan,a shorter size at maturity and the longer generation time,more cumulative eggs for each adult and more eggs per brood,higher net reproductive rate and intrinsic growth rate.D.similoides was more competitive than D.galeata in terms of growth,development and reproduction.4.The threshold food concentrations?TFC?of D.similoides was lower than D.galeata at 25?.When food concentration is a limiting factor,D.similoides has more competitive advantages than D.galeata.