15 results found
Scheuerl T, Kaitala V, 2021, The effect of dilution on eco-evolutionary dynamics of experimental microbial communities, Ecology and Evolution
Changing environmental conditions can infer structural modifications of predator-prey communities. New conditions often increase mortality which reduces population sizes. Following this, predation pressure may decrease until populations are dense again. Dilution may thus have substantial impact not only on ecological but also on evolutionary dynamics because it amends population densities. Experimental studies, in which microbial populations are maintained by a repeated dilution into fresh conditions after a certain period, are extensively used approaches allowing us to obtain mechanistic insights into fundamental processes. By design, dilution, which depends on transfer volume (modifying mortality) and transfer interval (determining the time of interaction), is an inherent feature of these experiments, but often receives little attention. We further explore previously published data from a live predator-prey (bacteria and ciliates) system which investigated eco-evolutionary principles and apply a mathematical model to predict how various transfer volumes and transfer intervals would affect such an experiment. We find not only the ecological dynamics to be modified by both factors but also the evolutionary rates to be affected. Our work predicts that the evolution of the anti-predator defense in the bacteria, and the evolution of the predation efficiency in the ciliates, both slow down with lower transfer volume, but speed up with longer transfer intervals. Our results provide testable hypotheses for future studies of predator-prey systems, and we hope this work will help improve our understanding of how ecological and evolutionary processes together shape composition of microbial communities.
<jats:title>Abstract</jats:title><jats:p>In this work I analyse how proportions of fatal cases after COVID-19 infection change since outbreak of the disease. Using publicity available data I model the change in deaths probability from day 30 of outbreak until 25 April 2020. The global trend is that the proportion of fatal cases is still increasing and that many countries have not yet reached the maximum deaths proportion. However, there are visual differences between countries and in some countries the proportions are clearly below or above the global trend. A positive correlation between deaths cases and recorded infections indicates that a higher infection number results in increased mortality numbers.</jats:p>
Scheuerl T, Kaitala V, 2020, Mortality and coexistence time both cause changes in predator-prey co-evolutionary dynamics
<jats:title>Abstract</jats:title><jats:p>All organisms are sensitive to the abiotic environment, and in multispecies communities a deteriorating environment increasing mortality and limiting coexistence time can cause ecological changes. When interaction within the community is changed this can impact co-evolutionary processes. Here we use a mathematical model to predict ecological and evolutionary changes in a simple predator-prey community under different mortality rates and times of coexistence, both controlled by various transfer volume and transfer interval. In the simulated bacteria-ciliate system, we find species densities to be surprisingly robust under changed mortality rates and times both species coexist, resulting in stable densities. Confirming a theoretical prediction however, the evolution of anti-predator defence in the bacteria and evolution of predation efficiency in ciliates relax under high mortalities and limited times both partners interact. In contrast, evolutionary trajectories intensify when global mortalities are low, and the predator-prey community has more time for close interaction. These results provide testable hypotheses for future studies of predator-prey systems and we hope this work will help to bridge the gap in our knowledge how ecological and evolutionary process together shape composition of microbial communities.</jats:p>
Kaitala V, Hiltunen T, Becks L, et al., 2020, Co-evolution as an important component explaining microbial predator-prey interaction, JOURNAL OF THEORETICAL BIOLOGY, Vol: 486, ISSN: 0022-5193
Scheuerl T, Hopkins M, Nowell R, et al., 2020, Bacterial adaptation is constrained in complex communities, Nature Communications, Vol: 11, ISSN: 2041-1723
A major unresolved question is how bacteria living in complex communities respond to environmental changes. In communities, biotic interactions may either facilitate or constrain evolution depending on whether the interactions expand or contract the range of ecological opportunities. A fundamental challenge is to understand how the surrounding biotic community modifies evolutionary trajectories as species adapt to novel environmental conditions. Here we show that community context can dramatically alter evolutionary dynamics using a novel approach that ‘cages’ individual focal strains within complex communities. We find that evolution of focal bacterial strains depends on properties both of the focal strain and of the surrounding community. In particular, there is a stronger evolutionary response in low-diversity communities, and when the focal species have a larger genome and are initially poorly adapted. We see how community context affects resource usage and detect genetic changes involved in carbon metabolism and inter-specific interaction. The findings demonstrate that adaptation to new environmental conditions should be investigated in the context of interspecific interactions.
Scheued T, Cairns J, Becks L, et al., 2019, Predator coevolution and prey trait variability determine species coexistence, PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 286, ISSN: 0962-8452
Scheuerl T, Stelzer C-P, 2019, Asexual reproduction changes predator population dynamics in a life predator-prey system, POPULATION ECOLOGY, Vol: 61, Pages: 210-216, ISSN: 1438-3896
Scheuerl T, Stelzer C-P, 2017, Sex initiates adaptive evolution by recombination between beneficial loci, PLOS ONE, Vol: 12, ISSN: 1932-6203
Current theory proposes that sex can increase genetic variation and produce high fitness genotypes if genetic associations between alleles at different loci are non-random. In case beneficial and deleterious alleles at different loci are in linkage disequilibrium, sex may i) recombine beneficial alleles of different loci, ii) liberate beneficial alleles from genetic backgrounds of low fitness, or iii) recombine deleterious mutations for more effective elimination. In our study, we found that the first mechanism dominated the initial phase of adaptive evolution in Brachionus calyciflorus rotifers during a natural selection experiment. We used populations that had been locally adapted to two environments previously, creating a linkage disequilibrium between beneficial and deleterious alleles at different loci in a combined environment. We observed the highest fitness increase when several beneficial alleles of different loci could be recombined, while the other mechanisms were ineffective. Our study thus provides evidence for the hypothesis that sex can speed up adaptation by recombination between beneficial alleles of different loci, in particular during early stages of adaptive evolution in our system. We also suggest that the benefits of sex might change over time and state of adaptive progress.
Barraclough TG, Bell TDC, Rivett D, et al., 2016, Resource-dependent attenuation of species interactions during bacterial succession, ISME Journal, Vol: 10, Pages: 2259-2268, ISSN: 1751-7362
Bacterial communities are vital for many economically and ecologically important processes. The role of bacterial community composition in determining ecosystem functioning depends critically on interactions among bacterial taxa. Several studies have shown that, despite a predominance of negative interactions in communities, bacteria are able to display positive interactions given the appropriate evolutionary or ecological conditions. We were interested in how interspecific interactions develop over time in a naturalistic setting of low resource supply rates. We assembled aquatic bacterial communities in microcosms and assayed the productivity (respiration and growth) and substrate degradation while tracking community composition. The results demonstrated that while bacterial communities displayed strongly negative interactions during the early phase of colonisation and acclimatisation to novel biotic and abiotic factors, this antagonism declined over time towards a more neutral state. This was associated with a shift from use of labile substrates in early succession to use of recalcitrant substrates later in succession, confirming a crucial role of resource dynamics in linking interspecific interactions with ecosystem functioning.
Barraclough TG, Bell T, Scheuerl T, 2015, Saturating effects of species diversity on life-history evolution in bacteria, Proceedings of the Royal Society of London. Series B, Biological Sciences, Vol: 282, ISSN: 0080-4649
Species interactions can play a major role in shaping evolution in new environments. In theory, species interactions can either stimulate evolution by promoting coevolution or inhibit evolution by constraining ecological opportunity. The relative strength of these effects should vary as species richness increases, and yet there has been little evidence for evolution of component species in communities. We evolved bacterial microcosms containing between 1 and 12 species in three different environments. Growth rates and yields of isolates that evolved in communities were lower than those that evolved in monocultures, consistent with recent theory that competition constrains species to specialize on narrower sets of resources. This effect saturated or reversed at higher levels of richness, consistent with theory that directional effects of species interactions should weaken in more diverse communities. Species varied considerably, however, in their responses to both environment and richness levels. Mechanistic models and experiments are now needed to understand and predict joint evolutionary dynamics of species in diverse communities.
Scheuerl T, Stelzer C-P, 2013, Patterns and dynamics of rapid local adaptation and sex in varying habitat types in rotifers, Ecology and Evolution, Vol: 3, Pages: 4253-4264, ISSN: 2045-7758
Local adaptation is an important principle in a world of environmental changeand might be critical for species persistence. We tested the hypothesis thatreplicated populations can attain rapid local adaptation under two varying laboratoryenvironments. Clonal subpopulations of the cyclically parthenogeneticrotifer Brachionus calyciflorus were allowed to adapt to two varying harsh and abenign environment: a high-salt, a food-limited environment and untreatedculture medium (no salt addition, high food). In contrast to most previousstudies, we re-adjusted rotifer density to a fixed value (two individuals per ml)every 3–4 days of unrestricted population growth, instead of exchanging a fixedproportion of the culture medium. Thus our dilution regime specificallyselected for high population growth during the entire experiment and it allowedus to continuously track changes in fitness (i.e., maximum population growthunder the prevailing conditions) in each population. After 56 days (43 asexualand eight sexual generations) of selection, the populations in the harsh environmentsshowed a significant increase in fitness over time relative to the beginningcompared to the population in untreated culture medium. Furthermore,the high-salt population exhibited a significantly elevated ratio of sexual offspringfrom the start of the experiment, which suggested that this environmenteither triggered higher rates of sex or that the untreated medium and the foodlimitedenvironment suppressed sex. In a following assay of local adaptation wemeasured population fitness under “local” versus “foreign” conditions (populationsadapted to this environment compared to those of the other environment)for both harsh habitats. We found significantly higher fitness values forthe local populations (on average, a 38% higher fitness) compared to theforeign populations. Overall, local adaptation was formed rapidly and it seemedto be more pronounced in the high-salt treatment.
Hahn MW, Scheuerl T, Jezberová J, et al., 2012, The passive yet successful way of planktonic life: genomic and experimental analysis of the ecology of a free-living polynucleobacter population, PLOS One, Vol: 7, ISSN: 1932-6203
BACKGROUND: The bacterial taxon Polynucleobacter necessarius subspecies asymbioticus represents a group of planktonic freshwater bacteria with cosmopolitan and ubiquitous distribution in standing freshwater habitats. These bacteria comprise <1% to 70% (on average about 20%) of total bacterioplankton cells in various freshwater habitats. The ubiquity of this taxon was recently explained by intra-taxon ecological diversification, i.e. specialization of lineages to specific environmental conditions; however, details on specific adaptations are not known. Here we investigated by means of genomic and experimental analyses the ecological adaptation of a persistent population dwelling in a small acidic pond. FINDINGS: The investigated population (F10 lineage) contributed on average 11% to total bacterioplankton in the pond during the vegetation periods (ice-free period, usually May to November). Only a low degree of genetic diversification of the population could be revealed. These bacteria are characterized by a small genome size (2.1 Mb), a relatively small number of genes involved in transduction of environmental signals, and the lack of motility and quorum sensing. Experiments indicated that these bacteria live as chemoorganotrophs by mainly utilizing low-molecular-weight substrates derived from photooxidation of humic substances. CONCLUSIONS: Evolutionary genome streamlining resulted in a highly passive lifestyle so far only known among free-living bacteria from pelagic marine taxa dwelling in environmentally stable nutrient-poor off-shore systems. Surprisingly, such a lifestyle is also successful in a highly dynamic and nutrient-richer environment such as the water column of the investigated pond, which was undergoing complete mixis and pronounced stratification in diurnal cycles. Obviously, metabolic and ecological versatility is not a prerequisite for long-lasting establishment of abundant bacterial populations under highly dynamic environmental conditions. Caut
Scheuerl T, Riss S, Stelzer CP, 2011, Phenotypic effects of an allele causing obligate parthenogenesis in a rotifer, Journal of Heredity, Vol: 102, Pages: 409-415, ISSN: 1465-7333
Transitions to obligate asexuality have been documented in almost all metazoan taxa, yet the conditions favoring such transitions remained largely unexplored. We address this problem in the rotifer Brachionus calyciflorus. In this species, a polymorphism at a single locus, op, can result in transitions to obligate parthenogenesis. Homozygotes for the op allele reproduce strictly by asexual reproduction, whereas heterozygous clones (+/op) and wild-type clones (+/+) are cyclical parthenogens that undergo sexual reproduction at high population densities. Here, we examine dosage effects of the op allele by analyzing various life-history characteristics and population traits in 10 clones for each of the 3 possible genotypes (op/op, +/op, and +/+). For most traits, we found that op/op clones differed significantly (P < 0.05) from the 2 cyclical parthenogenetic genotypes (+/+ and +/op). By contrast, the 2 cyclical parthenogenetic genotypes were almost indistinguishable, except that heterozygote individuals were slightly but significantly smaller in body size compared with wild-type individuals. Overall, this indicates that the op allele is selectively neutral in the heterozygous state. Thus, selective sweeps of this allele in natural populations would first require conditions favoring the generation of homozygotes. This may be given by inbreeding in very small populations or by double mutants in very large populations.
Hahn MW, Lang E, Brandt U, et al., 2009, Emended description of the genus Polynucleobacter and the species Polynucleobacter necessarius and proposal of two subspecies, P. necessarius subsp. necessarius subsp nov and P. necessarius subsp asymbioticus subsp nov., INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY, Vol: 59, Pages: 2002-2009, ISSN: 1466-5026
<jats:p id="p1">All organisms are susceptible to the environment and changingenvironmental conditions can infer structural modifications inpredator-prey communities. A change in the environment can influence,for example, the mortality rate of both the prey and the predator, ordetermine how long the interaction between both partners is. This mayhave a substantial impact on ecological, but also evolutionary dynamics.Experimental studies, in which microbial populations are maintained by arepeated dilution into fresh conditions after a certain period of time,are able to dissipate underlying mechanisms in a controlled way. Bydesign, dilution rate (modifying mortality) and transfer interval(determining the time of interaction) are crucial factors, but theyoften receive little attention in experimental design. We study datafrom a live predator-prey (bacteria and ciliates) system used to gaininsight into eco-evolutionary principles and apply a mathematical modelto predict how various dilution rates and transfer intervals wouldaffect such an experiment. We find the ecological dynamics to besurprisingly robust for both factors. However, the evolutionary ratesare expected to be affected. Our work predicts that the evolution of theanti-predator defence in the bacteria, and the evolution of thepredation efficiency in the ciliates, both decrease with higher dilutionrate, but increase with longer transfer intervals. Our results providetestable hypotheses for future studies of predator-prey systems and wehope this work will help improving our understanding how ecological andevolutionary processes together shape composition of microbialcommunities.</jats:p>
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