Cell-growth gene expression reveals a direct fitness cost of grazer-induced toxin production in red tide dinoflagellate prey

Induced prey defences against consumers are conspicuous in microbes, plants and animals. In toxigenic prey, a defence fitness cost should result in a trade-off between defence expression and individual growth. Yet, previous experimental work has failed to detect such induced defence cost in toxigenic phytoplankton. We measured a potential direct fitness cost of grazer-induced toxin production in a red tide dinoflagellate prey using relative gene expression (RGE) of a mitotic cyclin gene (cyc), a marker that correlates to cell growth. This approach disentangles the reduction in cell growth from the defence cost from the mortality by consumers. Treatments where the dinoflagellate Alexandrium catenella were exposed to copepod grazers significantly increased toxin production while decreasing RGE of cyc, indicating a defence-growth trade-off. The defence fitness cost represents a mean decrease of the cell growth rate of 32%. Simultaneously, we estimate that the traditional method to measure mortality loss by consumers is overestimated by 29%. The defence appears adaptive as the prey population persists in quasi steady state after the defence is induced. Our approach provides a novel framework to incorporate the fitness cost of defence in toxigenic prey–consumer interaction models.     

A lifetime perspective on foraging and mortality

Food intake carries many potential risks which may impair an animal's reproductive success not only in the current breeding cycle, but also for the rest of its lifetime. We examine the lifetime trade-off between the costs and benefits of food intake by presenting a simple animal foraging model, where each unit of food eaten carries with it a risk of mortality. We show that the optimal food intake rate over an animal's lifetime, for both semelparous and iteroparous animals, is not maximal. Instead, animals are required to strike a balance between the immediate reproductive benefits of gathering food and the future reproductive costs incurred by the food's mortality risk. This balance depends upon the lifespan of the animal as well as the nature of the risk. Different mortality risks are compared and it is shown that a mortality risk per unit time spent foraging is not, in general, equivalent to a mortality risk per unit of food consumed. The results suggest that a mortality risk per unit of food consumed, such as that presented by the presence of a toxin or of a parasite in the diet, has important consequences for feeding behaviour and is a possible factor involved in food intake regulation.     

An evolutionary model of stature, age at first birth and reproductive success in Gambian women

We have built a model to predict optimal age at first birth for women in a natural fertility population. The only existing fully evolutionary model, based on Ache hunter-gatherers, argues that as women gain weight, their fertility (rate of giving birth) increases-thus age at first birth represents a trade-off between time allocated to weight gain and greater fertility when mature. We identify the life-history implications of female age at first birth in a Gambian population, using uniquely detailed longitudinal data collected from 1950 to date. We use height rather than weight as an indicator of growth as it is more strongly correlated with age at first birth. Stature does not greatly influence fertility in this population but has a significant effect on offspring mortality. We model age at first reproduction as a trade-off between the time spent growing and reduced infant mortality after maturation. Parameters derived from this population are fitted to show that the predicted optimal mean age of first birth, which maximizes reproductive success, is 18 years, very close to that observed. The reaction norm associated with variation in growth rate during childhood also satisfactorily predicts the variation in age at first birth.     

Evolutionary classification of toxin mediated interactions in microorganisms

A trade-off between the parameters of Lotka–Volterra systems is used to give verifications of relations between intrinsic growth rate and limiting capacity and the stability type of the resulting dynamical system. The well known rock–paper–scissors game serves as a template for toxin mediated interactions, which is best represented by the bacteriocin producing Escherichia coli bacteria. There, we have three strains of the same species. The producer produces a toxin lethal to the sensitive, while the resistant is able to protect itself from that toxin. Due to the fact that there are costs for production and for resistance, a dynamics similar to the rock–paper–scissors game results. By using an adaptive dynamics approach for competitive Lotka–Volterra systems and assuming an inverse relation (trade-off) between intrinsic growth rate (IGR) and limiting capacity (LC) we obtain evolutionary and convergence stable relations between the IGR’s and the LC’s. Furthermore this evolutionary process leads to a phase topology of the population dynamics with a globally stable interior fixed point by leaving the interaction parameters constant. While the inverse trade-off stabilizes coexistence and does not allow branching, toxicity itself can promote diversification. The results are discussed in view of several biological examples indicating that the above results are structurally valid.     

Phenotypic plasticity and optimal timing of metamorphosis under uncertain time constraints

Life-history theory suggests that optimal timing of metamorphosis should depend on growth conditions and time constraints under which individuals develop. Current models cannot make reliable predictions for species in ephemeral habitats where individuals often face an increasing mortality risk over time because these models assume time-invariant mortality rates (i.e., daily mortality rates remain constant) and fixed seasons. We examined the plasticity of growth, development, and body mass at metamorphosis in tadpoles of the tree-hole breeding frog Phrynobatrachus guineensis in relation to an unpredictable time constraint in the field and in controlled experiments along a fixed density and food gradient. Mean mass and age at metamorphosis of sibships were positively correlated with per capita food level. Based on our results, we developed a simple model of the optimal timing of metamorphosis under time-dependent mortality rates showing that development rates are not only adjusted to growth conditions but also to time-variant mortality rates. The increasing mortality rate represents a time constraint that favors a reduced larval period, but because it is based on probabilities of survival it allows a trade-off between development time and mass. We extend this model to different types of time constraints and show that it can predict the range of documented reaction norms. Differences between species in␣the correlation of age and mass at metamorphosis may have evolved due to differences in their time-variant mortality rates.     

Determination of T-2 toxin,HT-2 toxin,and three other type A trichothecenes in layer feed by high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS)—comparison of two sample preparation methods

A sensitive method for the simultaneous determination of T-2 toxin, HT-2 toxin, neosolaniol, T-2 triol, and T-2 tetraol in layer feed using high-performance liquid chromatography coupled to triple quadrupole mass spectrometry in the positive ionization mode (LC-ESI-MS/MS) is described. Two fast and easy clean-up methods—with BondElut Mycotoxin and MycoSep 227 columns, respectively—were tested. The separation of the toxins was conducted on a Pursuit XRs Ultra 2.8 HPLC column using 0.13 mM ammonium acetate as eluent A and methanol as eluent B. Detection of the mycotoxins was carried out in the multiple reaction monitoring (MRM) mode using ammonium adducts as precursor ions. Quantification of all analytes was performed with d₃-T-2 toxin as an internal standard. The clean-up method with MycoSep 227 columns gave slightly better results for layer feed compared to the method using BondElut Mycotoxin columns (MycoSep 227: recovery between 50 and 63 %, BondElut Mycotoxin: recovery between 32 and 67 %) and was therefore chosen as the final method. The limits of detection ranged between 0.9 and 7.5 ng/g depending on the mycotoxin. The method was developed for the analysis of layer feed used at carry-over experiments with T-2 toxin in laying hens. For carry-over experiments, it is necessary that the method includes not only T-2 toxin but also the potential metabolites in animal tissues HT-2 toxin, neosolaniol, T-2 triol, and T-2 tetraol which could naturally occur in cereals used as feed stuff as well.     

Sedimentation of Nodularia spumigena and distribution of nodularin in the food web during transport of a cyanobacterial bloom from the Baltic Sea to the Kattegat

Nodularia spumigena is a toxic cyanobacteria that blooms in the Baltic Sea every year. In the brackish water of the Baltic Sea, its toxin, nodularin, mainly affects the biota in the surface water due to the natural buoyancy of this species. However, the fate of the toxin is unknown, once the cyanobacteria bloom enters the more saline waters of the Kattegat. In order to investigate this knowledge gap, a bloom of N. spumigena was followed during its passage, carried by surface currents, from the Baltic Sea into the Kattegat area, through the Öresund strait. N. spumigena cells showed an increased cell concentration through the water column during the passage of the bloom (up to 130 10³ cells ml⁻¹), and cells (4.2 10³ cells ml⁻¹) could be found down to 20 m depth, below a pycnocline. Sedimentation trap samples from below the pycnocline (10–12 m depth) also showed an increased sedimentation of N. spumigena filaments during the passage of the bloom. The toxin nodularin was detected both in water samples (0.3–6.0 μg l⁻¹), samples of sedimenting material (a toxin accumulation rate of 20 μg m^-2 day⁻¹), zooplankton (up to 0.1 ng ind.⁻¹ in copepods), blue mussels (70–230 μg kg⁻¹ DW), pelagic and benthic fish (herring (1.0–3.4 μg kg⁻¹ DW in herring muscle or liver) and flounder (1.3-6.2 μg kg⁻¹ DW in muscle, and 11.7-26.3 μg kg⁻¹ DW in liver). A laboratory experiment showed that N. spumigena filaments developed a decreased buoyancy at increased salinities and that they were even sinking with a rate of up to 1,7 m day⁻¹ at the highest salinity (32 PSU). This has implications for the fate of brackish water cyanobacterial blooms, when these reach more saline waters. It can be speculated that a significant part of the blooms content of nodularin will reach benthic organisms in this situation, compared to blooms decaying in brackish water, where most of the bloom is considered to be decomposed in the surface waters.     

Bacterial growth and grazing loss in contrasting areas of North and South Atlantic

Samples were collected from the top 200 m of the water columnat 50 stations during two cruises in different, near equinoctialseasons on an Atlantic transect near the 20°W meridian between50°N and 50°S. These samples were analysed to determinecharacteristics of the heterotrophic bacterial populations.Flow cytometry was used to enumerate these bacteria and determinetheir average size so as to calculate their biomass. Heterotrophicbacterial production, and the rate of grazing of these bacteriaby heterotrophic nanoplankton in the main depth layers, weredetermined using ³H thymidine and ¹⁴C leucine techniques. Thebiomass of heterotrophic nanoplankton in these layers was determinedusing a glucosaminidase assay. Five provinces were distinguishedalong the transect and characterized by average values of allmeasured parameters. The relative composition and activity ofthe microbial community in the water columns within each provincechanged little between the two cruises. Lowest heterotrophicbacterial biomass of 1–2 mg C m^–3 and productionof 0.1–0.2 mg C m^–3 day^–1 were found in thenorthern and southern Atlantic gyres, and were relatively similarin both seasons. Biomass and production were 2–4 timeshigher in the northern and southern temperate waters, and inequatorial waters, than in the gyres and tended to show moreseasonal variation. Production and biomass in the layer belowthe pycnocline were lower by 10–30% and about 50%, respectively,than values determined in the surface mixed layer, and variedless with latitude. Depth-integrated values of these two parameterswere generally of similar size in the mixed water layer andthe layer of the chlorophyll maximum and pycnocline, and tendedto vary with season. The specific growth rate of heterotrophicbacteria was in the range 0.05 to 0.12 day^–1 in the topmixed layer at all latitudes. In spite of the elevated temperatures,bacterial growth appears to be restricted by a shortage of nutrientsso that the microbial community cycles very slowly, with a turnovertime of the order of 1 week or more. The depth-integrated biomassof heterotrophic nanoplankton was generally about 100% of theheterotrophic bacterial biomass in the same water. Grazing bythese nanoplankton at the rate measured could consume all ofthe new production of heterotrophic bacteria in all waters,and they probably control the populations of both heterotrophicand phototrophic bacteria.     

The effect of different initial density on Amphidinium carterae Hulburt and Krenia mikimotoi Hansen

The experimental study of the interaction between Amphidinium carterae Hulburt and Krenia mikim otoi Hansen is carried in ecological conditions..The results showed tha in single culture system,A.carterae and K.mikimotoi growth curves Karen Logistic growth model,different initial density ratio could have a significant impact on the growth of two microalgae:With the initial density increases,the exponential phase and stationary phase is due to come earlier,and instantaneous population growth rate(r)and environmental carrying capacity(K)decreased.     

Scrounging behavior regulates population dynamics

The integration of behavioral and population ecology is necessary when behavior both feeds into demographic parameters and depends on population parameters. We show that scrounging behavior, the exploitation of others' resources, can affect both demographic parameters and population dynamics, including the stability of interactions with prey. Scrounging is a common tactic and its pay-offs exhibit both density- and frequency-dependence. We demonstrate that scrounging can act as a population regulator through its effects on individuals' reproductive rate and mortality. We also explore its effects on predator-prey population dynamics and show that the presence of scrounging predators allows an increased predator population size and contributes to the regulation of both predator and prey populations. Behavioral ecologists will appreciate that although scrounging is often pictured as imposing a social foraging cost to group membership, at the population level it also allows higher numbers of both prey and predators to coexist at equilibrium.     

A one-dimensional model of vertical stratification of Lake Shira focussed on winter conditions and ice cover

In meromictic lakes such as Lake Shira, horizontal inhomogeneity is small in comparison with vertical gradients. To determine the vertical distribution of temperature, salinity, and density of water in a deep zone of a Lake Shira, or other saline lakes, a one-dimensional (in vertical direction) mathematical model is presented. A special feature of this model is that it takes into account the process of ice formation. The model of ice formation is based on the one-phase Stefan problem with the linear temperature distribution in the solid phase. A convective mixed layer is formed under an ice cover due to salt extraction in the ice formation process. To obtain analytical solutions for the vertical distribution of temperature, salinity, and density of water, we use a scheme of vertical structure in the form of several layers. In spring, the ice melts as top and bottom. These processes are taken into account in the model. The calculated profiles of salinity and temperature of Shira Lake are in good agreement with field measurement data for each season. Additionally, we focussed on the redox zone, which is the zone in which the aerobic layers of a water column meet the anaerobic ones. Hyperactivity of plankton communities is observed in this zone in lakes with hydrogen sulphide monimolimnion, and Lake Shira is among them. The location of the redox zone in the lake, which is estimated from field measurements, coincides with a sharp increase in density (the pycnocline) during autumn and winter. During spring and summer, the redox zone is deeper than the pycnocline. The location of pycnocline calculated with the hydro physical model is in good agreement with field measurement data.     

Advection-induced oxygen variability in the North Sea-Baltic Sea transition

Instances of strong oxygen variations are described for two shallow water stations in the Kattegat, situated at the fluctuating frontal zone between outflowing surface water from the Baltic and inflowing bottom water from the Skagerrak/North Sea.The events consist of both a rapid emergence and a rapid disappearance of oxygen-depletion. Changes in oxygen concentration amounted to more than 20 g m^–2 d^–1 for the total water columns. Such high rates of change can not be explained by net local bottom oxygen consumption (0.6 g m^–2 d^–1) or net local water oxygen consumption (1.6 g m^–2 d^–1). The oxygen variations were influenced by the local and regional meteorological conditions. The observed instance of shallow water oxygen-depletion was connected to upward movement of the pycnocline and associated advective transport of oxygen-depleted Kattegat bottom waters to a shallow water area. Similarly, rapid disappearance of the bottom water oxygen deficit in a shallow water area was found to depend more on pycnocline lowering in connection with advective transport, than on the effect of local wind driven mixing.     

Phylogenetic and functional diversity of Bacteria and Archaea in a unique stratified lagoon, the Clipperton atoll (N Pacific)

The Clipperton lagoon in the North Pacific Ocean has been isolated from the surrounding sea for c. 160 years. It has a stratified water column that comprises an oxic and brackish upper water layer (mixolimnion) and a deep sulfuric anoxic saline layer (monimolimnion), separated by a steep pycnocline. Here, we test whether the Clipperton lagoon with its distinctive physico-chemical features, geographic isolation, recent water column stratification, and large nutrient input harbors original microbial communities. The combination of capillary electrophoresis single-strand polymorphism (CE-SSCP) fingerprinting and sequencing of cloned bacterial and archaeal 16S rRNA genes, and functional genes for methanogenesis (mcrA), methanotrophy (pmoA), and sulfate reduction (dsrAB), revealed that microbial communities and pathways were highly stratified down the water column. The mixolimnion contained ubiquitous freshwater clades of Alpha- and Betaproteobacteria, while the pycnocline contained mostly green sulfur bacteria (phylum Chlorobi). Sequences of the upper layers were closely related to sequences found in other aquatic ecosystems, suggesting that they have a strong potential for dispersal and colonization. In contrast, the monimolimnion contained new deeply branching bacterial divisions within the OP11 cluster and the Bacteroidetes, and was the most diverse of the layers. The unique environmental conditions characterizing the deep layers of the lagoon may explain the novelty of the microbial communities found at the Clipperton atoll.     

Viruses' Life History: Towards a Mechanistic Basis of a Trade-Off between Survival and Reproduction among Phages

Life history theory accounts for variations in many traits involved in the reproduction and survival of living organisms, by determining the constraints leading to trade-offs among these different traits. The main life history traits of phages—viruses that infect bacteria—are the multiplication rate in the host, the survivorship of virions in the external environment, and their mode of transmission. By comparing life history traits of 16 phages infecting the bacteria Escherichia coli, we show that their mortality rate is constant with time and negatively correlated to their multiplication rate in the bacterial host. Even though these viruses do not age, this result is in line with the trade-off between survival and reproduction previously observed in numerous aging organisms. Furthermore, a multiple regression shows that the combined effects of two physical parameters, namely, the capsid thickness and the density of the packaged genome, account for 82% of the variation in the mortality rate. The correlations between life history traits and physical characteristics of virions may provide a mechanistic explanation of this trade-off. The fact that this trade-off is present in this very simple biological situation suggests that it might be a fundamental property of evolving entities produced under constraints. Moreover, such a positive correlation between mortality and multiplication reveals an underexplored trade-off in host–parasite interactions.     

Viruses' Life History: Towards a Mechanistic Basis of a Trade-Off between Survival and Reproduction among Phages

Life history theory accounts for variations in many traits involved in the reproduction and survival of living organisms, by determining the constraints leading to trade-offs among these different traits. The main life history traits of phages—viruses that infect bacteria—are the multiplication rate in the host, the survivorship of virions in the external environment, and their mode of transmission. By comparing life history traits of 16 phages infecting the bacteria Escherichia coli, we show that their mortality rate is constant with time and negatively correlated to their multiplication rate in the bacterial host. Even though these viruses do not age, this result is in line with the trade-off between survival and reproduction previously observed in numerous aging organisms. Furthermore, a multiple regression shows that the combined effects of two physical parameters, namely, the capsid thickness and the density of the packaged genome, account for 82% of the variation in the mortality rate. The correlations between life history traits and physical characteristics of virions may provide a mechanistic explanation of this trade-off. The fact that this trade-off is present in this very simple biological situation suggests that it might be a fundamental property of evolving entities produced under constraints. Moreover, such a positive correlation between mortality and multiplication reveals an underexplored trade-off in host–parasite interactions.     

Variabilité à court terme des propriétés physiques,chimiques et biologiques du Saguenay,fjord subarctique du Quebec (Canada)

Tidal variability of water mass characteristics has been assessed in the upper 100 metres of the Saguenay, a subarctic fjord in Québec, Canada. Temperature and salinity show a maximum variability in the 5-15 m layer in which vertical oscillations of a very sharp pycnocline are observed. Phosphates, nitrates and chlorophyll a are highly variable above this pycnocline during a tidal cycle, but dissolved oxygen content is remarkably stable in the whole water column. It is concluded that fluctuations of many variables in the subsurface waters might be large enough to hinder high rates of primary production.     

Killer-sensitive coexistence in metapopulations of micro-organisms

Many micro-organisms are known to produce efficient toxic substances against conspecifics and closely related species. The widespread coexistence of killer (toxin producer) and sensitive (non-producer) strains is a puzzle calling for a theoretical explanation. Based on stochastic cellular automaton simulations and the corresponding semi-analytical configuration-field approximation models, we suggest that metapopulation dynamics offers a plausible rationale for the maintenance of polymorphism in killer-sensitive systems. A slight trade-off between toxin production and population growth rate is sufficient to maintain the regional coexistence of toxic and sensitive strains, if toxic killing is a local phenomenon restricted to small habitat patches and local populations regularly go extinct and are renewed via recolonizations from neighbouring patches. Pattern formation on the regional scale does not play a decisive part in this mechanism, but the local manner of interactions is essential.     

Year class splitting in the woodlouse Philoscia muscorum explained through studies of growth and survivorship

Year class splitting has been observed in a population of the terrestrial isopod Philoscia muscorum (Scopoli) in a fixed dune grassland. In this population, individuals born in one season differentiate into two forms, one of which grows to maturity in one year, the other in two.
Laboratory investigations of growth, fecundity and survivorship of individuals showed fundamental positive relationships between rate of growth and the ambient temperature/day light regime and between parental size and the number of offspring produced. Size also affected survivorship, with adults surviving better than juveniles. A link between survivorship and the temperature/day light regime was only obvious in small juveniles.
No direct physiological cause for the year class split could be derived from the laboratory studies, but a trade-off between the need for delayed or early breeding could result in the patterns of growth and reproduction observed in the field population. Delayed breeding allows continued growth of adults and hence larger numbers of offspring. Early breeding allows more growth of juveniles which greatly improves their chances of winter survival.     

Scaling up phenotypic plasticity with hierarchical population models

Individuals respond to different environments by developing different phenotypes, which is generally seen as a mechanism through which individuals can buffer adverse environmental conditions and increase their fitness. To understand the consequences of phenotypic plasticity it is necessary to study how changing a particular trait of an individual affects either its survival, growth, reproduction or a combination of these demographic vital rates (i.e. fitness components). Integrating vital rate changes due to phenotypic plasticity into models of population dynamics allows detailed study of how phenotypic changes scale up to higher levels of integration and forms an excellent tool to distinguish those plastic trait changes that really matter at the population level. A modeling approach also facilitates studying systems that are even more complex: traits and vital rates often co-vary or trade-off with other traits that may show plastic responses over environmental gradients. Here we review recent developments in the literature on population models that attempt to include phenotypic plasticity with a range of evolutionary assumptions and modeling techniques. We present in detail a model framework in which environmental impacts on population dynamics can be followed analytically through direct and indirect pathways that importantly incorporate phenotypic plasticity, trait-trait and trait-vital rate relationships. We illustrate this framework with two case studies: the population-level consequences of phenotypic responses to nutrient enrichment of plant species occurring in nutrient-poor habitats and of responses to changes in flooding regimes due to climate change. We conclude with exciting prospects for further development of this framework: selection analyses, modeling advances and the inclusion of spatial dynamics by considering dispersal traits as well.     

An Assessment of the Annual Mortality Rate and Population Demographics Status in Birds Based on Ring-Recovery Data

A new method for assessing the annual mortality rate in bird populations is described. Ring recoveries from birds that died from various causes serve as the basis for such an assessment. The commonly accepted technique for such an assessment performed with the help of MARK software is laborious, yet fails to ensure a highly precise assessment. To calculate the mortality rate, we propose an exponential demographic model that is based on the geometric progression of a decrease in the annual numbers in some arbitrarily selected set of birds in a population. The equation of the model allows calculating the annual mortality rate of a bird population or even a species in a simple way, if the ringing data covers a vast area, for example, the territory of Russia. In addition, the proposed equation permits producing “a mortality pattern,” namely, to present a chart of interrelations between the theoretical and real rates of the decrease in numbers in a given cohort of birds. The interrelations between the theoretical and real annual mortality rates allow understanding the status of a bird population each year during a period of ringing and recovery collecting: this makes it possible to reveal the population trend about whether the population is stable or decreasing or increasing in numbers.