Effects Of Temperature And Food Stoichiometric Ratio On Life History Straits Of Four Daphnia Galeata Clones

Large cladocerans,Daphnia are the keystone herbivore in aquatic ecosystems.As Daphnia are P-rich consumers,they are more sensitive to dietary phosporus(P)limitation and temperature regulation than other zooplankton taxa.P deficiency may constrain the synthesis of ribosomes,reducing protein synthesis.Temperature is a central regulator of metabolism and more ribosomes are needed to maintain a given protein synthesis rate at low temperatures.Climate warming and eutrophication by excessive phosphorus inpute are common environmental problems in freshwater ecosystems,and we hypothesized that warming and P enrichment would increase the fitness of Daphnia.We examined the separate and interactive effects of temperature an food stoichiometry on life-history straits of four Daphnia galeata clones from Liuxihe Reservoir(oligo-mesotrophic),Yantan Reservoir(meso-eutrophic),Hongchaojiang Reservoir(eutrophic)and Qingshuijiang Reservoir(eutrophic)in South China.Reservoirs Liuxihe and Yantan are located in the north of the Tropic of Cancer,while reservoirs Hongchaojiang and Qingshuijiang in the south of the Tropic of Cancer.We manipulated temperature(20 and 25?)and food C:P ratio(400 and 1600)in a full factorial design.Food concentration was 1 mg C L^-1of Scenedesmus obliquus.Age at first reproduction was significantly shorter at high temperature than at low temperature,and tended to increase with the increasing of food C:P ratio for the four clones.Temperature and food quality had no interactive effect on age at first reproduction.Clones from the north of the Tropic of Cancer had longer age at first reproduction than clones from the south of the Tropic of Cancer.Both body size at first reproduction and first clutch size were significantly smaller at high temperature than at low temperature,and larger at low food C:P ratio than at high food C:P ratio for the four clones.Temperature and food quality had no interactive effect on body size at first reproduction and first clutch size.Both body size at first reproduction and first clutch size of clones from the north of the Tropic of Cancer were significantly larger than clones from the south of the Tropic of Cancer.Neonate somatic growth rate was significantly larger at high temperature than at low temperature,and tended to increase with the decreasing of food C:P ratio for the four clones.Temperature and food quality had no interactive effect on neonate somatic growth rate.Neonate somatic growth rate showed no significant difference among four clones.Intrinsic growth rate was significantly higher at low food C:P ratio than at high food C:P ratio,and food quality and temperature had a positive interactive effect on intrinsic growth rate.Compared with low temperature and high food C:P ratio,clones from the north of the Tropic of Cancer tended to increase their intrinsic growth rate by 44-50%,and clones from the south of the Tropic of Cancer increase by 27-28%under high temperature and low food C:P ratio.Our results suggest that both warming and P enrichment of food tend to make Daphnia galeata mature earlier.P enrichment of food tend to increase the offspring production of Daphnia galeata,while warming decrease the offspring production.Warming and P enrichment of food have a positive interactive effect on intrinsic growth rate,enhancing the fitness of Daphnia galeata.It is likely that clones from the north of the Tropic of Cancer have a higher fitness than clones from the south of the Tropic of Cancer under climate warming and P enrichment.It is helpful to explain the ecological mechanism of dominant species in subtropical reservoirs,and it is of great significance to study the response of water ecosystem to human activities and climate change.