Can climate warming save Daphnia from parasites? Reduced parasite prevalence in Daphnia populations from artificially heated lakes

Climate warming might modify infection outcomes and it has been proposed that temperature increase will result in a “sicker world.” We tested this hypothesis by comparing the prevalence of infection in a common freshwater host–parasite system (crustacean Daphnia infected with the ichthyosporean pathogen Caullerya mesnili) between five artificially heated lakes and four nearby non‐heated control lakes. The heated lakes, which receive warm water from two power plants, have experienced an elevation in water temperature of ca. 3–4°C for the last 60 yr. Analyses of 5 yr of field data revealed that Daphnia communities from heated lakes had lower parasite prevalence than communities from control sites. To disentangle a possible direct detrimental effect of elevated temperature on the parasite from differences in baseline levels of host resistance, we compared infection susceptibility between Daphnia clones isolated from heated and control lakes, under laboratory conditions at two different temperatures. Daphnia from heated lakes were less susceptible to infection than clones from control lakes, while experimental temperature did not affect infection outcome. The data did not confirm the “warmer hence sicker world” scenario. Instead, it seems that indirect effects of temperature elevation (via shifts in lake hydrology) may restrict its spread into heated lakes. Then, local adaptation to the host from control lakes further inhibits re‐establishment of the parasite from control to heated lakes. Our results underline the context‐dependency of the impact of temperature increase on host–parasite interactions

Can climate warming save Daphnia from parasites? Reduced parasite prevalence in Daphnia populations from artificially heated lakes

Climate warming might modify infection outcomes and it has been proposed that temperature increase will result in a “sicker world.” We tested this hypothesis by comparing the prevalence of infection in a common freshwater host–parasite system (crustacean Daphnia infected with the ichthyosporean pathogen Caullerya mesnili) between five artificially heated lakes and four nearby non‐heated control lakes. The heated lakes, which receive warm water from two power plants, have experienced an elevation in water temperature of ca. 3–4°C for the last 60 yr. Analyses of 5 yr of field data revealed that Daphnia communities from heated lakes had lower parasite prevalence than communities from control sites. To disentangle a possible direct detrimental effect of elevated temperature on the parasite from differences in baseline levels of host resistance, we compared infection susceptibility between Daphnia clones isolated from heated and control lakes, under laboratory conditions at two different temperatures. Daphnia from heated lakes were less susceptible to infection than clones from control lakes, while experimental temperature did not affect infection outcome. The data did not confirm the “warmer hence sicker world” scenario. Instead, it seems that indirect effects of temperature elevation (via shifts in lake hydrology) may restrict its spread into heated lakes. Then, local adaptation to the host from control lakes further inhibits re‐establishment of the parasite from control to heated lakes. Our results underline the context‐dependency of the impact of temperature increase on host–parasite interactions.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655Fundacja Uniwersytetu im. Adama Mickiewicza http://dx.doi.org/10.13039/100016906Ministerstwo Nauki i Szkolnictwa Wyższego http://dx.doi.org/10.13039/501100004569Narodowe Centrum Nauki http://dx.doi.org/10.13039/50110000428

Aphanizomenon gracile increases in width in the presence of Daphnia. A defence mechanism against grazing?

<p><em>Filamentous cyanobacteria are frequently consumed by grazers like </em>Daphnia<em>, which can break filaments and make them more readily available to filter-feeders. However, various defence mechanisms against grazing have also been observed in cyanobacteria. Data concerning changes in the morphology of filamentous algae, especially their width in the presence of a grazer, are scarce. Field studies of filament morphology of cyanobacteria relate their changes to nutrient availability and temperature. Moreover, filament morphology displays significant differences in filament length and width among seasons. We hypothesised that the morphological changes in filament observed in the field – especially their width – could be a defence mechanism that is induced by the presence of a grazer, such as </em>Daphnia<em>. Thus, two experiments were conducted in order to test the influence of </em>Daphnia <em>(direct grazing and infochemicals together in the first experiment) and the chemicals it released (grazing excluded, only chemicals present in the second experiment) on </em>Aphanizomenon gracile<em>’s morphology, in controlled laboratory conditions. </em>Aphanizomenon <em>filaments became significantly shorter and thicker in both experiments. However, </em>Daphnia<em>’s grazing combined with excreted chemicals had stronger effect than chemicals alone. To our knowledge, this is the first report describing the shortening and thickening of filaments in the presence of </em>Daphnia <em>infochemicals. It seems that the </em>Aphanizomenon <em>filaments in the presence of </em>Daphnia <em>switch their growing mode and invest more heavily in width than length. Our results support the hypothesis that </em>Daphnia <em>is at least partly responsible for the changes in filament width observed in the field. This could be a strategy that helps </em>Aphanizomenon <em>to withstand grazer’s pressure during early stages of a bloom.</em></p

Countergradient variation concealed adaptive responses to temperature increase in Daphnia from heated lakes

To test the general assumption that global warming will induce body size reduction in aquatic organisms, we used a system of lakes continually heated for six decades by warm water discharge from power plants. Their temperature elevation of 3–4°C corresponds with climate change forecasts for the end of the 21st century. We compared body size and reproduction of Daphnia longispina complex communities inhabiting heated and non‐heated (control) lakes nearby. No difference in body size was found, but Daphnia communities from heated lakes had a wider thermal breadth for reproduction. The two lake groups varied in the taxonomic composition of Daphnia communities. Thus, to disentangle inter‐ and intraspecific sources of variation, and to examine evolution vs. phenotypic plasticity of investigated traits, we performed two life history experiments: (1) a between‐species experiment compared D. galeata inhabiting heated lakes with D. longispina typical of nearby control lakes, under three temperature regimes; (2) a within‐species experiment compared D. galeata from heated lakes with conspecifics from high latitude (cold control) and low latitude (warm control) lakes, under two temperature regimes. The experiments revealed countergradient variation: environmental constraints on body size in situ concealed evolution of larger potential body size in Daphnia from heated lakes. In turn, evolution of increased body size plasticity resulted in an efficient resource allocation trade‐off: more effective reproduction at high temperature, at the cost of size reduction. We suggest that large size is adaptive during active overwintering, while plastic size reduction is a coping strategy for high temperatures.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655Ministerstwo Nauki i Szkolnictwa Wyższego http://dx.doi.org/10.13039/501100004569Narodowe Centrum Nauki http://dx.doi.org/10.13039/50110000428

Can climate warming save Daphnia from parasites? Reduced parasite prevalence in Daphnia populations from artificially heated lakes

Climate warming might modify infection outcomes and it has been proposed that temperature increase will result in a “sicker world.” We tested this hypothesis by comparing the prevalence of infection in a common freshwater host–parasite system (crustacean Daphnia infected with the ichthyosporean pathogen Caullerya mesnili) between five artificially heated lakes and four nearby non-heated control lakes. The heated lakes, which receive warm water from two power plants, have experienced an elevation in water temperature of ca. 3–4°C for the last 60 yr. Analyses of 5 yr of field data revealed that Daphnia communities from heated lakes had lower parasite prevalence than communities from control sites. To disentangle a possible direct detrimental effect of elevated temperature on the parasite from differences in baseline levels of host resistance, we compared infection susceptibility between Daphnia clones isolated from heated and control lakes, under laboratory conditions at two different temperatures. Daphnia from heated lakes were less susceptible to infection than clones from control lakes, while experimental temperature did not affect infection outcome. The data did not confirm the “warmer hence sicker world” scenario. Instead, it seems that indirect effects of temperature elevation (via shifts in lake hydrology) may restrict its spread into heated lakes. Then, local adaptation to the host from control lakes further inhibits re-establishment of the parasite from control to heated lakes. Our results underline the context-dependency of the impact of temperature increase on host–parasite interactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/175762/1/lno12257_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/175762/2/lno12257.pd

Differences in cell wall of thin and thick filaments of cyanobacterium Aphanizomenon gracile SAG 31.79 and their implications for different resistance to Daphnia grazing

Recent studies have shown that the filamentous cyanobacterium Aphanizomenon gracile Lemmermann, strain SAG 31.79, consists of two types of filaments that differ in thickness. These two types are known to vary in resistance to Daphnia magna grazing: thin filaments (&lt;2.5 µm) are more vulnerable to grazing than the thick ones (&gt;2.5 µm). In this study, we investigated whether the difference in the vulnerability to grazing of thin and thick filaments is a result of different thickness of their cell walls, a filament stiffness determinant. We expected thick filaments to have thicker cell walls than the thin ones. Additionally, we analysed whether cell wall thickness correlates with filament thickness regardless of the filament type. A morphometric analysis of cell walls was performed using transmission electron micrographs of ultra-thin sections of the batch-cultured cyanobacterial material.  Our study revealed that the thin type of filaments had thinner cell walls than the thick filaments. Moreover, cell wall thickness was positively correlated with filament thickness. TEM (transmission electron microscopy) observations also revealed that the thin type of filaments was often at different stages of autocatalytic cell destruction, which was mainly manifested in the increase in cell vacuolization and degradation of the cytoplasm content. Based on our findings, we assume that previously reported higher resistance of thick filaments to Daphnia grazing results from greater stiffness and excellent physiological conditions of thick filaments. </p

Niche Differentiation of Host-associated Pelagic Microbes and Their Potential Contribution to Biogeochemical Cycling in Artificially Warmed Lakes

It has been proposed that zooplankton-associated microbes provide numerous beneficial services to their “host”. However, there is still a lack of understanding concerning the effect of temperature on the zooplankton microbiome. Furthermore, it is unclear to what extent the zooplankton microbiome differs from free-living and phytoplankton-&-particle-associated (PPA) microbes. Here, we explicitly addressed these issues by investigating (1) the differences in free-living, PPA and zooplankton associated microbes; and (2) the impact of temperature on these microbes in the water column of a series of lakes artificially warmed by two power plants. High-throughput amplicon sequencing of the 16S rRNA gene showed that diversity and composition of the bacterial community associated to zooplankton, PPA, and bacterioplankton varied significantly from one another, grouping in different clusters indicating niche differentiation of pelagic microbes. From the abiotic parameters measured, temperature significantly affected the diversity and composition of all analysed microbiomes. Two phyla (e.g., Proteobacteria and Bacteroidetes) dominated in zooplankton microbiomes whereas Actinobacteria was the dominant phylum in the bacterioplankton. The microbial species richness and diversity was lower in zooplankton compared to bacterioplankton and PPA. Indicator species analysis showed that 9 %, 8 % 12 % and 21% unique OTUs were significantly associated with copepods, cladocerans, bacterioplankton, and PPA, respectively. Surprisingly, genera of methane oxidizing bacteria (MOB), methylotrophs and nitrifiers (e.g., Nitrobacter) significantly associated with the microbiome of zooplankton and PPA. Our study clearly demonstrates niche differentiation of pelagic microbes which is affected by warming with possible impact on biogeochemical cycling in freshwater systems

Biocidal effect of (E)-anethole on the cyanobacterium Aphanizomenon gracile Lemmermann

Biocidal natural substances of botanical origin offer a promising ecofriendly option for controlling toxic cyanobacteria. Herein, we study 11 essential oils and some of their major components for their activity on Aphanizomenon gracile. On the basis of our results we support that Origanum vulgare and O. dictamnus, Ocimum basilicum, Eucalyptus meliodora, Melissa officinalis, and Pimpinella anisum exhibited the strongest activities, and the IC50/1d values of the extracts were calculated to be between 168.43 and 241.97 μg mL−1. When the major components of the biocidal essential oils were tested individually, (E)-anethole was found active, exhibiting an IC50/1d value of 71.35 μg mL−1. On the other hand, the half-life (t1/2) of (E)-anethole was calculated at 1 h. A preliminary attempt of (E)-anethole microencapsulation was conducted, in order to slowly release this biocidal agent, increasing the residual life under open air conditions and thus the biological activity. Results were promising since the microencapsulated product exhibited better activity than did the non-formulated (E)-anethole. This is a first report on the biocidal activity of EOs and (E)-anethole on A. gracile and a preliminary indication of the microencapsulated (E)-anethole potential use as a natural biocidal in fresh waters

Effects of <i>Daphnia</i> exudates and sodium octyl sulphates on filament morphology and cell wall thickness of <i>Aphanizomenon gracile</i> (Nostocales), <i>Cylindrospermopsis raciborskii</i> (Nostocales) and <i>Planktothrix agardhii</i> (Oscillatoriales)

<p>Grazing is recognized as one of the selective factors shaping the morphology and physiology of cyanobacteria. A recent study has shown that the filamentous cyanobacterium <i>Aphanizomenon gracile</i> strain SAG 31.79 thickened in the presence of <i>Daphnia</i> (Cladocera) and its exudates. The aims of our study were: (1) to determine whether this type of response to <i>Daphnia</i> cues is common for other strains of <i>A. gracile</i>, and other species of filamentous cyanobacteria, (2) to test whether the response is due to nutrients recycled by <i>Daphnia</i>, or kairomone induced, and (3) whether it is related to toxin production. Prior to the experiment, cyanobacterial strains were inspected using chromatographic methods for the presence of two toxins, cylindrospermopsin (CYN) and three homologues of microcystin (MC-RR, MC-YR, MC-LR). HPLC analyses showed that all strains were free of cylindrospermopsin, whereas microcystins were detected only in one strain (<i>Planktothrix agardhii</i>). We then tested whether <i>Daphnia</i> exudates can cause thickening of cyanobacterial filaments, which would suggest the morphological changes in cyanobacterial filaments are caused by recycled nutrients. Cyanobacteria were also exposed to sodium octyl sulphate (a commercially available <i>Daphnia</i> kairomone). Transmission electron microscopy (TEM) was used to check whether <i>Daphnia</i> exudates and sodium octyl sulphate trigger thickening of cyanobacterial cell walls, which would be a defence mechanism against grazing. The TEM analysis revealed no significant effect of either <i>Daphnia</i> exudates or kairomone (sodium octyl sulphate) on the cell wall thickness of cyanobacteria. However, our study showed that <i>Daphnia</i> exudates triggered filament thickening in nostocalean cyanobacteria, while filaments of the oscillatorialean strain <i>P. agardhii</i> did not show this response. It was also demonstrated that sodium octyl sulphate alone can also cause filament thickening, which suggests that this might be a specific defence response to the presence of grazers.</p