Effect of food quality on life history traits of <i>Daphnia galeata</i> and <i>Bosmina fatalis</i>

Abstract

枝角类体内氮磷比与生活史策略的选择密切相关，大型枝角类通常体内含磷量高、个体生长快、生殖率高，而小型枝角类体内含磷量低，个体生长相对较慢、生殖率低.由于大型枝角类对磷的需求比较高，我们假设大型枝角类生活史各参数对食物磷缺乏比小型枝角类更为敏感.本研究比较分析了食物碳磷比对流溪河水库两种枝角类（盔型溞（Daphnia galeata）和脆弱象鼻溞（Bosmina fatalis））生活史各参数的影响.实验设计了3个食物质量处理组：高磷（碳：磷=105）、中磷（400）和低磷（1450），食物浓度均为2 mg C/L的蛋白核小球藻（Chlorella pyrenoidosa）.脆弱象鼻溞内禀增长率、幼溞生长速率、平均每窝产仔量和首次生殖时体长均随着食物碳磷比的升高而显著下降；首次生殖时间则随着食物碳磷比的升高而显著延长；新生幼溞体长在各食物处理中无显著差异.盔型溞幼溞生长速率、平均每窝产仔量和首次生殖时体长均随着食物碳磷比的升高而显著下降；内禀增长率和新生幼溞体长在高磷处理组显著高于中磷和低磷处理组，但在中磷和低磷处理组无显著差异；首次生殖时间在高磷处理组显著短于中磷和低磷处理组，但在中磷和低磷处理组无显著差异.结果表明，食物的磷缺乏降低了两种枝角类的内禀增长率和幼溞生长速率，并延长了性成熟时间；盔型溞的内禀增长率、首次生殖时间和平均每窝产仔量等生活史参数受食物磷限制的程度小于脆弱象鼻溞，导致盔型溞对脆弱象鼻溞有竞争优势.;Primary life history parameters of cladocerans are linked to body N:P stoichiometry. Large cladocerans tend to have higher phosphorus content, grow more rapidly, and produce more neonates than small cladocerans. The entire difference in specific phosphorus content of these two cladoceran groups can be related to differences in RNA content. Large cladocerans' high growth rate requires a high ribosomal complement for extensive protein synthesis coupled to high growth rate. Therefore, large cladocerans' life history straits are supposed to be more sensitive to food phosphorus deficiency than those of small cladocerans. We examined the effects of food stoichiometry quality (different carbon:phosphorus[C:P] ratios)on life history straits of two common cladocerans species in South China, Daphnia galeata and Bosmina fatalis. D. galeata and B. fatalis were fed saturating concentrations of food (Chlorella pyrenoidosa, 2 mg C/L)of high P (C:P=105), medium P (400), and low P (1450). Population intrinsic growth rates varied from 0.36 to 0.46 d^-1 and 0.18 to 0.39 d^-1, neonate body growth rates varied from 0.31 to 0.52 d^-1 and 0.10 to 0.38 d^-1, age at first reproduction varied from 4.6 to 7.2 d and 3.4 to 7.2 d, mean clutch size varied from 11.5 to 15.1 ind. and 1.6 to 2.3 ind., and newborn neonate body size varied from 0.65 to 0.71 mm and 0.22 to 0.23 mm for D. galeata and B. fatalis, respectively. Neonate body growth rate, population intrinsic growth rate, body size at first reproduction and mean clutch size tend to decrease, while age at first reproduction tend to increase with the increasing of food C:P ratio in both species. Newborn neonate body size was much higher under high P condition than those under medium and low P conditions in D. galeata, but showed no significant difference among treatments in B. fatalis. Our results suggest that population intrinsic growth rate, neonate growth rate and age at first reproduction of D. galeata tend to be less sensitive to food phosphorus deficiency than those of B. fatalis, and D. galeata is competitively superior to B. fatalis.