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The more, the merrier: heterotroph richness stimulates methanotrophic activity.
No full textAlthough microorganisms coexist in the same environment, it is still unclear how their interaction
regulates ecosystem functioning. Using a methanotroph as a model microorganism, we determined
how methane oxidation responds to heterotroph diversity. Artificial communities comprising of a
methanotroph and increasing heterotroph richness, while holding equal starting cell numbers were
assembled. We considered methane oxidation rate as a functional response variable. Our results
showed a significant increase of methane oxidation with increasing heterotroph richness,
suggesting a complex interaction in the cocultures leading to a stimulation of methanotrophic
activity. Therefore, not only is the methanotroph diversity directly correlated to methanotrophic
activity for some methanotroph groups as shown before, but also the richness of heterotroph
interacting partners is relevant to enhance methane oxidation too. In this unprecedented study, we
provide direct evidence showing how heterotroph richness exerts a response in methanotroph–
heterotroph interaction, resulting in increased methanotrophic activity. Our study has broad
implications in how methanotroph and heterotroph interact to regulate methane oxidation, and is
particularly relevant in methane-driven ecosystems
Contrasting effects of rising CO2 on primary production and ecological stoichiometry at different nutrient levels
No full textAlthough rising CO2 concentrations are thought to promote the growth and alter the carbon : nutrient stoichiometry of primary producers, several studies have reported conflicting results. To reconcile these contrasting results, we tested the following hypotheses: rising CO2 levels (1) will increase phytoplankton biomass more at high nutrient loads than at low nutrient loads, but (2) will increase their carbon : nutrient stoichiometry more at low than at high nutrient loads. We formulated a mathematical model to predict dynamic changes in phytoplankton population density, elemental stoichiometry and inorganic carbon chemistry in response to rising CO2. The model was tested in chemostat experiments with the freshwater cyanobacterium Microcystis aeruginosa. The model predictions and experimental results confirmed the hypotheses. Our findings provide a novel theoretical framework to understand and predict effects of rising CO2 concentrations on primary producers and their nutritional quality as food for herbivores under different nutrient conditions
The role of social environment on parental care: offspring benefit more from the presence of female than male helpers
No full text1.Investment in offspring depends on the costs and benefits to the carer, which can vary with sex and social status. Investment also depends on the effort of others by allowing for compensation (load-lightening), with biparental care studies showing that this depends on the state and type of the other carer. By contrast, studies on cooperative breeders have solely focussed on the effects of group size rather than its composition (i.e. social environment).
2.Here we propose and provide the first test of the ‘Social Environment’ hypothesis, that is, how the characteristics (here the sex) of other helpers present in the group affect parental care and how this in turn affects offspring fitness in cooperatively breeding red-winged fairy-wrens (Malurus elegans).
3.Breeders provisioned nestlings at a higher rate than helpers, but there was no sex difference in provisioning rate. Compensation to increasing group size varied little with sex and status, but strongly depended on social environment. All group members reduced their provisioning rates in response to an increasing number of male (load-lightening), but not female helpers (additive care).
4.As a result, nestlings received more food and grew faster in the presence of female helpers. The increased nestling growth did convey a fitness advantage due to a higher post-fledging survival to adulthood.
5.Our study provides the first evidence that parental care can depend on social environment. This could be an important overlooked aspect to explain variation in parental care in cooperative breeders in general and in particular the enormous variation between the sexes, which we reveal in a literature overview.
Epigenetic variation in asexually reproducing organisms
No full textThe role that epigenetic inheritance can play in adaptation may differ between sexuals and asexuals because (1) the dynamics of adaptation differ under sexual and asexual reproduction and the opportunities offered by epigenetic inheritance may affect these dynamics differently; and (2) in asexual reproduction epigenetic reprogramming mechanisms that are associated with meiosis can be bypassed, which could promote the buildup of epigenetic variation in asexuals. Here, we evaluate current evidence for an epigenetic contribution to adaptation in asexuals. We argue that two aspects of epigenetic variation should have particular relevance for asexuals, namely epigenetics-mediated phenotypic plasticity within and between generations, and heritable variation via stochastic epimutations. An evaluation of epigenetic reprogramming mechanisms suggests that some, but not all, forms of asexual reproduction enhance the likelihood of stable transmission of epigenetic marks across generations compared to sexual reproduction. However, direct tests of these predicted sexual–asexual differences are virtually lacking. Stable transmission of DNA methylation, transcriptomes, and phenotypes from parent to clonal offspring are demonstrated in various asexual species, and clonal genotypes from natural populations show habitat-specific DNA methylation. We discuss how these initial observations can be extended to demonstrate an epigenetic contribution to adaptation.
Distinguishing autotrophic and heterotrophic respiration based on diel oxygen change curves: revisiting Dr. Faustus
No full text* In his paper ‘Climate change, nutrient pollution and the bargain of Dr. Faustus’, Moss (Freshwater Biology, 55, 2010, 175) described the interacting and mutually reinforcing effects of climate change and nutrient pollution on aquatic ecosystems. * Among other things, Moss (Freshwater Biology, 55, 2010, 175) proposed a simple method for determining autotrophic and heterotrophic respiration rates (Ra and Rh) based on the diel oxygen change technique. Here, we show that one of the assumptions on which the method is based is flawed and that Ra and Rh cannot be derived mathematically from diel oxygen change curves. [KEYWORDS: autotrophs ecosystem respiration heterotrophs methods primary production]
Impact of elevated pCO2 on paralytic shellfish poisoning toxin content and composition in Alexandrium tamarense
No full textOcean acidification is considered a major threat to marine ecosystems and may particularly affect primary producers. Here we investigated the impact of elevated pCO2 on paralytic shellfish poisoning toxin (PST) content and composition in two strains of Alexandrium tamarense, Alex5 and Alex2. Experiments were carried out as dilute batch to keep carbonate chemistry unaltered over time. We observed only minor changes with respect to growth and elemental composition in response to elevated pCO2. For both strains, the cellular PST content, and in particular the associated cellular toxicity, was lower in the high CO2 treatments. In addition, Alex5 showed a shift in its PST composition from a non-sulfated analogue towards less toxic sulfated analogues with increasing pCO2. Transcriptomic analyses suggest that the ability of A. tamarense to maintain cellular homeostasis is predominantly regulated on the post-translational level rather than on the transcriptomic level. Furthermore, genes associated to secondary metabolite and amino acid metabolism in Alex5 were down-regulated in the high CO2 treatment, which may explain the lower PST content. Elevated pCO2 also induced up-regulation of a putative sulfotransferase sxtN homologue and a substantial down-regulation of several sulfatases. Such changes in sulfur metabolism may explain the shift in PST composition towards more sulfated analogues. All in all, our results indicate that elevated pCO2 will have minor consequences for growth and elemental composition, but may potentially reduce the cellular toxicity of A. tamarense.
No effects of experimental warming but contrasting seasonal patterns for soil peptidase and glycosidase enzymes in a sub-arctic peat bog
No full textThe nature of linkages between soil C and N cycling is important in the context of terrestrial ecosystem responses to global environmental change. Extracellular enzymes produced by soil microorganisms drive organic matter decomposition, and are considered sensitive indicators of soil responses to environmental variation. We investigated the response of eight hydrolytic soil enzymes (four peptidases and four glycosidases) to experimental warming in a long-term climate manipulation experiment in a sub-arctic peat bog, to determine to what extent the response of these two functional groups are similar. We found no significant effect of experimental spring and summer warming and/or winter snow addition on either the potential activity or the temperature sensitivity (of Vmax) of any of the enzymes. However, strong and contrasting seasonal patterns in both variables were observed. All of the peptidases, as well as alpha-glucosidase, had lower potential activity at the end of summer (August) compared to the beginning (June). Conversely, beta-glucosidase had significantly higher potential activity in August. Peptidases had consistently higher temperature sensitivities in June compared to August, while all four glycosidases showed the opposite pattern. Our results suggest that warming effects on soil enzymes are small compared to seasonal differences, which are most likely mediated by the seasonality of substrate supply and microbial nutrient demand. Furthermore the contrasting seasonal patterns for glycosidases and peptidases suggest that enzyme-based models of soil processes need to allow for potential divergence between the production and activity of these two enzyme functional groups.