Production of protoplasts from the fungi Curvularia inaequalis and Trichoderma reesei

Summary Protoplast formation in Curvularia inaequalis was achieved using non-commercial and commercial snail gut enzymes or Trichoderma harzianum enzymes. The cells were grown for enzyme treatment on cellophane sheets or in liquid cultures for varying periods of time. The production of T. harzianum enzymes is discussed. The highest protoplast yields were 2.6x10⁷ protoplasts/ml enzyme solution. Protoplasts were shown to have zero to four nuclei. Protoplast regeneration was succesfully carried out in semisolid agar.     

Loss of Competition in the Outside Host Environment Generates Outbreaks of Environmental Opportunist Pathogens

Environmentally transmitted pathogens face ecological interactions (e.g., competition, predation, parasitism) in the outside-host environment and host immune system during infection. Despite the ubiquitousness of environmental opportunist pathogens, traditional epidemiology focuses on obligatory pathogens incapable of environmental growth. Here we ask how competitive interactions in the outside-host environment affect the dynamics of an opportunist pathogen. We present a model coupling the classical SI and Lotka–Volterra competition models. In this model we compare a linear infectivity response and a sigmoidal infectivity response. An important assumption is that pathogen virulence is traded off with competitive ability in the environment. Removing this trade-off easily results in host extinction. The sigmoidal response is associated with catastrophic appearances of disease outbreaks when outside-host species richness, or overall competition pressure, decreases. This indicates that alleviating outside-host competition with antibacterial substances that also target the competitors can have unexpected outcomes by providing benefits for opportunist pathogens. These findings may help in developing alternative ways of controlling environmental opportunist pathogens.     

Genetic and environmental variation in performance of a marine isopod: effects of eutrophication

Environmental variation in food resources modifies performance of herbivores, in addition to genetic variation and maternal effects. In marine benthic habitats, eutrophication may modify herbivores diets by changing host species composition or nutritional quality of algae for herbivores. We studied experimentally the effects of diet breadth and nutrient availability for the host algae on fitness components of the herbivorous isopod Idotea baltica. We fed the adult isopods with the brown algae Fucus vesiculosus and Pilayella littoralis and juveniles with the green alga Cladophora glomerata. By using half-sib families, we were able to separate the genetic, environmental and maternal effects on intermolt duration and size of the juveniles. The mothers confined to the diet consisting of both Fucus and Pilayella grew better and produced larger egg mass than those having consumed Fucus alone. Nutrient enhancement of algae did not influence the performance of the adult herbivores. However, the juveniles achieved twice the weight as well as shorter intermolt duration when consuming nutrient-treated C. glomerata. Mothers nutrition, either nutrient enrichment of her food algae or diet breadth, did not affect juvenile survival or growth as such, but we found evidence that the broader diet consumed by the mother mediated offspring performance by further accelerating growth rate of the offspring that fed on nutrient-treated alga. Intermolt duration was a highly heritable trait, but size showed very low heritability. Instead, maternal effects on size were substantial, suggesting that differences among mothers in their egg-provisioning ability strongly affect weight gain of their offspring. A high amount of additive genetic variance in intermolt duration implies potential for quick evolutionary responses in the growth schedule in the face of changes in the selective environment. We conclude that eutrophication, in addition to improving growth and reproduction of I. baltica by enhancing food quality and by providing opportunity for broader, more profitable diets, may act as a selective agent on life-history traits. Eutrophication of coastal waters is thus likely to reflect in herbivore density, population dynamics and eventually, grazing pressure of littoral macroalgae.     

Mate-search efficiency can determine the evolution of separate sexes and the stability of hermaphroditism in animals

Limited availability of mating partners has been proposed as an explanation for the occurrence of simultaneous hermaphroditism in animals with pair mating. When low population density or low mobility of a species limits the number of potential mates, simultaneous hermaphrodites may have a selective advantage because, first, they are able to adjust the allocation of resources between male and female functions in order to maximize fitness; second, in a hermaphroditic population the likelihood of meeting a partner is higher because all individuals are potential mates; and, third, in the absence of mating partners, many simultaneously hermaphroditic animals have the option of reproducing through self-fertilization. Recognizing that mate availability is central to the existing theory of hermaphroditism in animals, it is important to examine the effects of mate search on predictions of the stability of hermaphroditism. Many hermaphroditic animals can increase the number of potential mates they contact by active searching. However, since mate search has costs in terms of time and energy, the increased number of potential mates will be traded off against the amount of resources that can be allocated to the production of gametes. We explore the consequences of this trade-off to the evolution of mating strategies and to the selective advantage of self-fertilization. We show that in low and moderate population densities, poor mate-search efficiency and high costs of searching stabilize hermaphroditism and bias sex allocation toward female function. In addition, in very low population densities, there is strong selective advantage for self-fertilization, but this advantage decreases considerably in species with high mate-search efficiency. Most important, however, we present a novel evolutionary prediction: when mate search is efficient, disruptive frequency-dependent selection on time allocation to mate search leads to the evolution of searching and nonsearching phenotypes and, ultimately, to the evolution of males and females.     

Environmental Variation Generates Environmental Opportunist Pathogen Outbreaks

Many socio-economically important pathogens persist and grow in the outside host environment and opportunistically invade host individuals. The environmental growth and opportunistic nature of these pathogens has received only little attention in epidemiology. Environmental reservoirs are, however, an important source of novel diseases. Thus, attempts to control these diseases require different approaches than in traditional epidemiology focusing on obligatory parasites. Conditions in the outside-host environment are prone to fluctuate over time. This variation is a potentially important driver of epidemiological dynamics and affect the evolution of novel diseases. Using a modelling approach combining the traditional SIRS models to environmental opportunist pathogens and environmental variability, we show that epidemiological dynamics of opportunist diseases are profoundly driven by the quality of environmental variability, such as the long-term predictability and magnitude of fluctuations. When comparing periodic and stochastic environmental factors, for a given variance, stochastic variation is more likely to cause outbreaks than periodic variation. This is due to the extreme values being further away from the mean. Moreover, the effects of variability depend on the underlying biology of the epidemiological system, and which part of the system is being affected. Variation in host susceptibility leads to more severe pathogen outbreaks than variation in pathogen growth rate in the environment. Positive correlation in variation on both targets can cancel the effect of variation altogether. Moreover, the severity of outbreaks is significantly reduced by increase in the duration of immunity. Uncovering these issues helps in understanding and controlling diseases caused by environmental pathogens.     

Bottom-up and cascading top-down control of macroalgae along a depth gradient

On marine rocky shores, macroalgal herbivory is often intense, such that the cascading effects of fish predation may contribute to the control of algal communities. To estimate the magnitudes of top-down and bottom-up control on a macroalgal community, we manipulated the access of carnivorous fish to macroalgal colonization substrates, as well as nutrient availability, at two sub-littoral depths. There were three levels of fish manipulation: natural fish community, no fish and the enclosure of one common species, the perch, Perca fluviatilis. We found a clear cascade effect of fish predation on both the total density and several individual species of macroalgae, which was more pronounced in deep than shallow water. The density of the dominant grazers, i.e. snails, increased in nutrient-enriched conditions; perch were inefficient in controlling herbivores, and had therefore no cascading effect on algal densities under such conditions. Although nutrients enhanced the growth of opportunistic algae, herbivores, in the absence of fish, inhibited this response. While algal diversity was higher in shallow than in deep water, the enrichment effect was opposite at the two depths with lowered diversity in the shallows and increased at depth. Our results indicate that fish predation is an efficient regulator of meso-herbivores and that its effect thereby cascades onto the producer trophic level such that both perennial and opportunistic algae benefit from the presence of fish. This cascade effect is probably stronger at depth where predation efficiency is less disturbed by wave motion.     

High-performance liquid chromatographic analysis of phlorotannins from the brown alga Fucus vesiculosus

Separating individual compounds by HPLC represents an effective method for the detection and quantification of phenolic compounds and has been widely utilised. However, phlorotannins are commonly quantified using colorimetric methods, as the total amount of the whole compound group. In the present paper the separation of a set of individual soluble phlorotannins from the phenolic crude extract of Fucus vesiculosus was achieved by HPLC with UV photodiode array detection. Different gradient programs for reversed- and normal-phase HPLC methods were developed and tested. Normal-phase (NP) conditions with a silica stationary phase and a mobile phase with a linear gradient of increasing polarity were found to separate 16 individual components of the phenolic extract. The suitability of the NP-HPLC method for mass spectrometric application was preliminarily tested. Sample preparation was found to be a critical step in the analysis owing to the rapid oxidation of phlorotannins; ascorbic acid was used as an antioxidant.     

Genotypic variation in tolerance and resistance to fouling in the brown alga <Emphasis Type="Italic">Fucus vesiculosus</Emphasis>

In this study, we examined genetic variation in resistance and tolerance to fouling organisms in the brown alga Fucus vesiculosus. We first grew 30 algal genotypes in the field, where we allowed fouling organisms to colonise the genotypes at natural levels. We then conducted a manipulative experiment, where we grew 20 genotypes of algae in aquaria with or without fouling organisms. We measured host resistance as the load of fouling organisms and tolerance as the slope of the regression of algal performance on fouling level. Fouling organisms decreased host growth and contents of phlorotannins and thus have the potential to act as selective agents on algal defenses. We found significant among-genotype variation in both resistance and tolerance to fouling. We did not find a trade-off between resistance and tolerance. We found a marginally significant cost of resistance, but no cost of tolerance. Our results thus indicate that both the tolerance and resistance of F. vesiculosus can evolve as a response to fouling and that the costs of resistance may maintain genetic variation in resistance.     

Responses of growth and phlorotannins in <Emphasis Type="Italic">Fucus vesiculosus</Emphasis> to nutrient enrichment and herbivory

Discharge from anthropogenic sources may modify both macroalgal growth patterns and resource allocation to carbon based secondary compounds, thereby affecting their susceptibility for herbivory. We tested the effect of eutrophication in terms of nutrient enhancement on growth and phlorotannin concentration of Fucus vesiculosus by conducting manipulative experiments in the field and mesocosms. In the field experiment we utilised fish farms as nutrient sources and in the mesocosm-experiment we manipulated ambient nutrient levels and occurrence of the herbivorous isopod Idotea baltica. Vicinity of a fish farm affected neither growth nor the phlorotannin concentration of Fucus but increased the amount of epiphytes growing on Fucus. Other organisms such as epiphytic filamentous algae and periphyton, which are more capable of quickly utilizing excess nutrients, may restrain the direct effects of nutrient enhancement on Fucus. In a manipulative mesocosm experiment, neither nutrient enrichment nor occurrence of herbivores affected phlorotannin concentration implying lack of induced defences, at least in terms of increasing phlorotannin concentration. Feeding of thallus decreased the growth rate of algae, but the number of reproductive organs, receptacles, was not affected by herbivory. The negative effect of herbivory on the amount of apical tips tended to be stronger under nutrient enriched conditions. We conclude that eutrophication processes, in terms of nutrient enrichment, does not have strong direct effect on growth or phlorotannin production of F. vesiculosus. However, there may be important indirect consequences. First, herbivory may be targeted more to apical parts of the thallus under eutrophicated conditions. Second, the result that Fucus growing close to nutrient sources were smaller than those in control areas may reflect differences in mortality schedules of algae between eutrophicated and control areas.     

Conditions for the spread of conspicuous warning signals: a numerical model with novel insights

The initial evolution of conspicuous warning signals presents an evolutionary problem because selection against rare conspicuous signals is presumed to be strong, and new signals are rare when they first arise. Several possible solutions have been offered to solve this apparent evolutionary paradox, but disagreement persists over the plausibility of some of the proposed mechanisms. In this paper, we construct a deterministic numerical simulation model that allows us to derive the strength of selection on novel warning signals in a wide range of biologically relevant situations. We study the effects of predator psychology (learning, rate of mistaken attacks, and neophobia) on selection. We also study the how prey escape, predation intensity, number of predators, and abundance of different prey types affects selection. The model provides several important results. Selection on novel warning signals is number rather than frequency dependent. In most cases, there exists a threshold number of aposematic individuals below which aposematism is selected against and above which aposematism is selected for. Signal conspicuousness (which increases detection rate) and distinctiveness (which allows predator to distinguish defended from nondefended prey) have opposing effects on evolution of warning signals. A more conspicuous warning signal cannot evolve unless it makes the prey more distinctive from palatable prey, reducing mistaken attacks by predators. A novel warning signal that is learned quickly can spread from lower abundance more easily than a signal that is learned more slowly. However, the relative rate at which the resident signal and the novel signal are learned is irrelevant for the spread of the novel signal. Long-lasting neophobia can facilitate the spread of novel warning signals. Individual selection via the ability of defended prey to escape from predator is not likely to facilitate evolution of conspicuous warning signals if both the resident (cryptic) morph and the novel morph have the same escape probability. Predation intensity (defined as the proportion of palatable prey eaten by the predator) has a strong effect on selection. More intense predation results in strong selection against rare signals, but also strong selective advantage to common signals. The threshold number of aposematic individuals is lower when predation is intense. Thus, the evolution of warning signals may be more likely in environments where predation is intense. The effect of numbers of predators depends on whether predation intensity also changes. When predation intensity is constant, increasing numbers of predators raises the threshold number of aposematic individuals, and thus makes evolution of aposematism more difficult. If predation intensity increases in parallel with number of predators, the threshold number of aposematic individuals does not change much, but selection becomes more intense on both sides of the threshold.