@article{EinumFossenParryetal.2019, author = {Einum, Sigurd and Fossen, Erlend I. F. and Parry, Victor and Pelabon, Christophe}, title = {Genetic variation in metabolic rate and correlations with other energy budget components and life history in Daphnia magna}, series = {Evolutionary Biology}, volume = {46}, journal = {Evolutionary Biology}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0071-3260}, doi = {10.1007/s11692-019-09473-x}, pages = {170 -- 178}, year = {2019}, abstract = {Much is known about the genetic variance in certain components of metabolism, most notably resting and maximum metabolic rate. This is in stark contrast to the lack of information on genetic variance in the metabolic rate of individuals that feed and express routine activity, and how this rate correlates with other components of the energy budget or life history traits. Here we quantify genetic variance in metabolic rate (MR) under such conditions, as well as food consumption, juvenile somatic growth rate and age at maturation under ad lib food availability in a set of 10 clones of Daphnia magna from a natural population. Broad sense evolvabilities (0.16 0.56\%) were on the same order of magnitude as those typically observed for physiological and life history traits, and suggest that all these traits have the potential to evolve within this population. We did not find support for the previously hypothesized positive genetic correlation between metabolic rate and growth rate. Rather, the patterns of genetic correlations suggest that genetic variance in food consumption is the single most influential trait shaping somatic growth rate, but that additional variance in growth can be explained by considering the joint effect of consumption and MR. The genetic variance in consumption and MR also translated into genetic variance in age at maturation, creating a direct link between these energy budget components and a life history trait with strong fitness effects. Moreover, a weak positive correlation between MR and food consumption suggests the presence of substantial amounts of independent genetic control of these traits, consistent with results obtained using genomic approaches.}, language = {en} } @phdthesis{Guislain2019, author = {Guislain, Alexis}, title = {Eco-physiological consequences of fluctuating light on phytoplankton}, doi = {10.25932/publishup-46927}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-469272}, school = {Universit{\"a}t Potsdam}, pages = {161}, year = {2019}, abstract = {Phytoplankton growth depends not only on the mean intensity but also on the dynamics of the light supply. The nonlinear light-dependency of growth is characterized by a small number of basic parameters: the compensation light intensity PARcompμ, where production and losses are balanced, the growth efficiency at sub-saturating light αµ, and the maximum growth rate at saturating light µmax. In surface mixed layers, phytoplankton may rapidly move between high light intensities and almost darkness. Because of the different frequency distribution of light and/or acclimation processes, the light-dependency of growth may differ between constant and fluctuating light. Very few studies measured growth under fluctuating light at a sufficient number of mean light intensities to estimate the parameters of the growth-irradiance relationship. Hence, the influence of light dynamics on µmax, αµ and PARcompμ are still largely unknown. By extension, accurate modelling predictions of phytoplankton development under fluctuating light exposure remain difficult to make. This PhD thesis does not intend to directly extrapolate few experimental results to aquatic systems - but rather improving the mechanistic understanding of the variation of the light-dependency of growth under light fluctuations and effects on phytoplankton development. In Lake TaiHu and at the Three Gorges Reservoir (China), we incubated phytoplankton communities in bottles placed either at fixed depths or moved vertically through the water column to mimic vertical mixing. Phytoplankton at fixed depths received only the diurnal changes in light (defined as constant light regime), while phytoplankton received rapidly fluctuating light by superimposing the vertical light gradient on the natural sinusoidal diurnal sunlight. The vertically moved samples followed a circular movement with 20 min per revolution, replicating to some extent the full overturn of typical Langmuir cells. Growth, photosynthesis, oxygen production and respiration of communities (at Lake TaiHu) were measured. To complete these investigations, a physiological experiment was performed in the laboratory on a toxic strain of Microcystis aeruginosa (FACBH 1322) incubated under 20 min period fluctuating light. Here, we measured electron transport rates and net oxygen production at a much higher time resolution (single minute timescale). The present PhD thesis provides evidence for substantial effects of fluctuating light on the eco-physiology of phytoplankton. Both experiments performed under semi-natural conditions in Lake TaiHu and at the Three Gorges Reservoir gave similar results. The significant decline in community growth efficiencies αµ under fluctuating light was caused for a great share by different frequency distribution of light intensities that shortened the effective daylength for production. The remaining gap in community αµ was attributed to species-specific photoacclimation mechanisms and to light-dependent respiratory losses. In contrast, community maximal growth rates µmax were similar between incubations at constant and fluctuating light. At daily growth saturating light supply, differences in losses for biosynthesis between the two light regimes were observed. Phytoplankton experiencing constant light suffered photo-inhibition - leading to photosynthesis foregone and additional respiratory costs for photosystems repair. On the contrary, intermittent exposure to low and high light intensities prevented photo-inhibition of mixed algae but forced them to develop alternative light strategy. They better harvested and exploited surface irradiance by enhancing their photosynthesis. In the laboratory, we showed that Microcystis aeruginosa increased its oxygen consumption by dark respiration in the light few minutes only after exposure to increasing light intensities. More, we proved that within a simulated Langmuir cell, the net production at saturating light and the compensation light intensity for production at limiting light are positively related. These results are best explained by an accumulation of photosynthetic products at increasing irradiance and mobilization of these fresh resources by rapid enhancement of dark respiration for maintenance and biosynthesis at decreasing irradiance. At the daily timescale, we showed that the enhancement of photosynthesis at high irradiance for biosynthesis of species increased their maintenance respiratory costs at limiting light. Species-specific growth at saturating light µmax and compensation light intensity for growth PARcompμ of species incubated in Lake TaiHu were positively related. Because of this species-specific physiological tradeoff, species displayed different light affinities to limiting and saturating light - thereby exhibiting a gleaner-opportunist tradeoff. In Lake TaiHu, we showed that inter-specific differences in light acquisition traits (µmax and PARcompμ) allowed coexis¬tence of species on a gradient of constant light while avoiding competitive exclusion. More interestingly we demonstrated for the first time that vertical mixing (inducing fluctuating light supply for phytoplankton) may alter or even reverse the light utilization strategies of species within couple of days. The intra-specific variation in traits under fluctuating light increased the niche space for acclimated species, precluding competitive exclusion. Overall, this PhD thesis contributes to a better understanding of phytoplankton eco-physiology under fluctuating light supply. This work could enhance the quality of predictions of phytoplankton development under certain weather conditions or climate change scenarios.}, language = {en} } @article{AttermeyerGrossartFluryetal.2017, author = {Attermeyer, Katrin and Grossart, Hans-Peter and Flury, Sabine and Premke, Katrin}, title = {Bacterial processes and biogeochemical changes in the water body of kettle holes - mainly driven by autochthonous organic matter?}, series = {Aquatic sciences : research across boundaries}, volume = {79}, journal = {Aquatic sciences : research across boundaries}, publisher = {Springer}, address = {Basel}, issn = {1015-1621}, doi = {10.1007/s00027-017-0528-1}, pages = {675 -- 687}, year = {2017}, abstract = {Kettle holes are small inland waters formed from glacially-created depressions often situated in agricultural landscapes. Due to their high perimeter-to-area ratio facilitating a high aquatic-terrestrial coupling, kettle holes can accumulate high concentrations of organic carbon and nutrients, fueling microbial activities and turnover rates. Thus, they represent hotspots of carbon turnover in the landscape, but their bacterial activities and controlling factors have not been well investigated. Therefore, we aimed to assess the relative importance of various environmental factors on bacterial and biogeochemical processes in the water column of kettle holes and to disentangle their variations. In the water body of ten kettle holes in north-eastern Germany, we measured several physico-chemical and biological parameters such as carbon quantity and quality, as well as bacterial protein production (BP) and community respiration (CR) in spring, early summer and autumn 2014. Particulate organic matter served as an indicator of autochthonous production and represented an important parameter to explain variations in BP and CR. This notion is supported by qualitative absorbance indices of dissolved molecules in water samples and C: N ratios of the sediments, which demonstrate high fractions of autochthonous organic matter (OM) in the studied kettle holes. In contrast, dissolved chemical parameters were less important for bacterial activities although they revealed strong differences throughout the growing season. Pelagic bacterial activities and dynamics might thus be regulated by autochthonous OM in kettle holes implying a control of important biogeochemical processes by internal primary production rather than facilitated exchange with the terrestrial surrounding due to a high perimeter-to-area ratio.}, language = {en} }