The studies of differences in life history and suitability of both water temperatures and trophic levels among rotifer sibling species improve our understanding of speciation, sibling species coexistence and possible niche differentiation over space and time, and consequences for the functioning of ecosystems induced by climate change and eutrophication. We collected Brachionus calyciflorus from Lake Baixiang and Lake Kongque, two tropical shallow lakes, in Xishuangbanna city, Yunnan, China, clonally cultured them in laboratory, and found that the B. calyciflorus complex contains two sibling species named sibling species BNA13 and BNB3 by phylogenetic analysis, and investigated the life-table parameters of the two sibling species BNA13 and BNB3 at four temperatures (16, 20, 24 and 28°C) and four algal densities (0.5, 1.0, 2.0 and 4.0×106 cells.mL−1 ). The results showed that the responses to increasing temperature and algal density for each of the life-table parameters differed with rotifer sibling species. Sibling species, temperature, algal density and their interactions almost all significantly affected the durations of juvenile period, embryonic development, reproductive period, post-reproductive period, mean lifespan, net reproductive rate, generation time and intrinsic rate of population growth. Sibling species significantly affected the age-specific survivorship. Temperature, algal density and their interaction and the interaction of sibling species and temperature significantly affected the age-specific fecundity. Regardless of the effects of temperature and algal density, the durations of juvenile period, embryonic development, reproductive period, post-reproductive period and mean lifespan, age-specific survivorship, net reproductive rate and generation time of the B. calyciflorus sibling species BNA13 were greater than those of BNB3, but the intrinsic rate of population growth of BNA13 was lower than those of BNB3. This suggests that the two B. calyciflorus sibling species adopted variable life history strategies, low population growth and high survivorship for sibling species BNA13, and high population growth and low survivorship for sibling species BNB3. Both the intrinsic rates of population growth of BNA13 and BNB3 were the highest at 28°C and 4.0×106 cells.mL−1 algal density, indicating that some adaptations of the B. calyciflorus sibling species BNA13 and BNB3 in tropical shallow lakes to water temperatures and trophic levels were similar, and they have the potential for coexistence in single waterbody of higher temperature and higher trophic level.

/pdf/differences-in-life-history-characteristics-between-two-2qtt9799rg.pdf

Differences in life history characteristics between two sibling species in Brachionus calyciflorus complex from tropical shallow lakes

Shallow lakes are important for the maintenance of Lake Poyang ecosystem integrity, and zooplankton play an important role in its substance and energy flow. We investigated zooplankton in spring (April), summer (July), autumn (October) and winter (January of the following year) from 2012 to 2016 in a sub-lake of Lake Poyang with seasonal water level fluctuations. The study aims to understand their seasonal dynamics and interannual variation of zooplankton community in relation to environmental variables. A total of 115 species were identified in all samples of the 4 years, comprising 87 Rotifera, 13 Cladocera and 15 Copepoda. Rotifera was the dominant group in quantity and its species richness and abundance were significantly higher than Cladocera and Copepoda (P<0.05, by ANOVA), while Cladocera dominated in biomass. Species richness of Rotifera showed a significant seasonal difference (P<0.05 by ANOVA). The clear decline of zooplankton species richness in spring was mainly due to the dramatic decrease of Rotifera species. Furthermore, both density and biomass of zooplankton showed significant seasonal differences (P<0.05). Generally, the density and biomass of zooplankton were higher in summer and autumn than in winter and spring. Biodiversity indices e.g., Shannon-Wiener index and evenness were dramatically lower in spring than in other seasons. Non-metric multidimensional scaling (NMDS) analysis suggested that the zooplankton communities can be divided into three groups: spring community, summer–autumn community and winter community associated with distinct indicator species. The results of species richness and community analysis showed that the seasonal succession of zooplankton communities did not have interannual reproducibility. Redundancy analysis revealed that water temperature (WT), conductivity, pH and dissolved oxygen (DO) had significant effects on the zooplankton community. In addition, water level fluctuations, disturbance by wintering waterbirds and artificial water level control during dry season have potential effects on zooplankton community structure too. This study is helpful to further understand the ecosystem stability of lake connected with rivers and provide scientific guidance for protection of lake wetlands.

Seasonal and inter-annual community structure characteristics of zooplankton driven by water environment factors during different hydrological years in a sub-lake of Lake Poyang, China

Adaptation of Brachionus calyciflorus(Rotifera) occurred in winter in Lake Tingtang to water temperature: a life table demography study

Keratella tropica and Keratella valga are very similar in external morphology. K. tropica is a warm water species, and occurs in tropical and subtropical regions. K. valga is a eurythermal and widespread species. In subtropical shallow lakes, K. tropica has a higher density than K. valga . In the present study, K. tropica and K. valga were collected, respectively, from Lake Tingtang and Lake Jinghu in Wuhu city, Anhui, China, and their life history variables were compared at four levels (0.5×106 , 1.0×106 , 2.0×106 and 4.0×106 cells.mL−1 ) of Scenedesmus obliquus at 20°C. The results showed that both rotifer species had the same response to increasing food levels as regards duration of reproductive and post-reproductive periods, average lifespan, life expectancy at hatching, generation time, net reproductive rate and intrinsic rate of population increase, but differed in their duration of pre-reproductive period. The duration of pre-reproductive period of the rotifers was significantly affected by food level, species and their interaction (P were longer or higher than those of K. valga . The higher density of K. tropica in subtropical lakes might be attributed to its longer lifespan and higher reproductive rate.

/pdf/the-effects-of-food-level-on-the-life-history-variables-of-265lbdan4e.pdf

The effects of food level on the life history variables of the two closely related rotifer species Keratella tropica and Keratella valga

Background Sub-lakes are important for the maintenance of the ecosystem integrity of Lake Poyang, and zooplankton play an important role in its substance and energy flow. Methods A seasonal investigation of zooplankton was conducted in spring (April), summer (July), autumn (October) and winter (January of the following year) from 2012 to 2016 in a sub-lake of Lake Poyang. The aim of the present study was to understand the seasonal dynamics and interannual variation of zooplankton communities and their relationship to environmental factors. Results A total of 115 species were identified in all samples in the four years, which comprised of 87 Rotifera, 13 Cladocera and 15 Copepoda. Rotifera was the dominant group in terms of quantity, and its species richness and abundance were significantly higher when compared to Cladocera and Copepoda (P < 0.05), while Cladocera dominated in terms of biomass. The species richness of Rotifera exhibited a significant seasonal difference (P < 0.05). Both the density and biomass of zooplankton revealed significant seasonal differences (P < 0.05). In general, the density and biomass of zooplankton were higher in summer and autumn, when compared to winter and spring. Biodiversity indices were dramatically lower in spring than in the other seasons. The non-metric multidimensional scaling (NMDS) analysis suggested that these zooplankton communities can be divided into three groups: spring community, summer-autumn community, and winter community. The seasonal succession of zooplankton communities did not have interannual reproducibility. In high water level years, the dominant species of zooplankton (Cladocerans and Copepods) in the wet season had a lower density, and the result in low water level years was exactly the opposite. The redundancy analysis revealed that water temperature (WT), conductivity, pH and dissolved oxygen (DO) had significant effects on the zooplankton community. Conclusions The community structure of zooplankton has a significant seasonal pattern, but has no interannual repeatability. In high water level years, the dominant species of zooplankton (Cladocerans and Copepods) in the wet season had a lower density, and the result in low water level years was exactly the opposite. The density, biomass and diversity indices of zooplankton were significantly different in different seasons. The present study was helpful in the further understanding of the ecosystem stability of lakes connected with rivers, providing scientific guidance for the protection of lake wetlands.

Seasonal and inter-annual community structure characteristics of zooplankton driven by water environment factors in a sub-lake of Lake Poyang, China.

Effects of temperature(15,20,25and 30℃) and Scenedesmus obliquus density(1.0×106,3.0×106 and 5.0×106cells/ml) on life history parameters including life expectancy at hatching,generation time,gross reproductive rate,net reproductive rate,intrinsic rate of population increase and proportion of sexual offspring of Brachionus diversicornis were studied by means of individual culture.Results showed that temperature affected significantly life expectancy at hatching,generation time,gross reproductive rate,net reproductive rate and intrinsic rate of population increase,but did not affect proportion of sexual offspring.Food level affected markedly gross reproductive rate and net reproductive rate,but had no effect on life expectancy at hatching,generation time,intrinsic rate of population increase and proportion of sexual offspring.The interaction between food level and temperature did not significantly influence all the life table demographic parameters.Both the life expectancy at hatching and the generation time decreased with increasing temperature.The lowest and highest net reproductive rate was obtained at 15 and 30℃,respectively;while with no difference between 20 and 25℃.The gross reproductive rate was lower at 15℃ than those at 20,25and 30℃,and no difference was observed among those at the latter three temperatures.Both the net reproductive rate and the gross reproductive rate were higher at 3.0×106cells/ml than those at 1.0×106 and 5.0×106cells/ml of Scenedesmus obliquus,and those at the two latter food levels were similar.

/pdf/wen-du-he-shi-wu-mi-du-dui-lie-zu-bi-wei-lun-chong-19h5ct4wxq.pdf

温度和食物密度对裂足臂尾轮虫(Brachionus diversicornis)生命表统计学参数的影响

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温度和食物密度对裂足臂尾轮虫(Brachionus diversicornis)生命表统计学参数的影响