Narrow Results

This study presents a comprehensive model of predator–prey interactions within a toxic environment, with a particular focus on the effect of toxicant compounds on the development of populations. By incorporating environmental disturbances, the dynamics of the model are investigated to enhance the system’s authenticity. Analytical explanations have been provided for the deterministic system solutions, including positivity, uniform boundedness and persistence. The deterministic portion of the investigation entails a comprehensive examination of occurrence and stability criteria pertaining to every possible equlibria. The bifurcation studies conducted on the system exhibit the appearance of local bifurcations, including transcritical, saddle-node and Hopf bifurcations. Moreover, these evaluations establish the parametric region in which Bautin, Bogdanov–Takens and cusp bifurcation occur. Under a relevant selection of parametric values, the suggested system has the capacity to manifest a wide range of dynamic phenomena, such as bi-stable behavior, emergence of limit cycles, and presence of homoclinic loops. Furthermore, in a stochastic environment, the use of Lyapunov functions explains the existence of a global positive solution. It has additionally been argued that the proposed system exhibits ultimate stochastic boundedness. Subsequently, specific and adequate criteria demonstrate the eradication of both species as well as the long-term survival of prey communities. We have also investigated the impact of the exogenous input rate of toxic substances and the coefficient of toxic substances in both species on the behavior of the whole system, both in deterministic and stochastic scenarios. Theoretical findings have been confirmed by various numerical investigations.

Toxic or allelopathic compounds liberated by toxin-producing phytoplankton (TPP) acts as a strong mediator in plankton dynamics. On an analysis of a set of phytoplankton biomass data that have been collected by our group in the northwest part of the Bay of Bengal, and by analysis of a three-component mathematical model under a constant as well as a stochastic environment, we explore the role of toxin-allelopathy in determining the dynamic behavior of the competing phytoplankton species. The overall results, based on analytical and numerical wings, demonstrate that toxin-allelopathy due to the TPP promotes a stable co-existence of those competitive phytoplankton that would otherwise exhibit competitive exclusion of the weak species. Our study suggests that TPP might be a potential candidate for maintaining the co-existence and diversity of competing phytoplankton species.

In this paper, the issue on the optimal harvesting of fish catching after eliminating toxin during the fish aquaculture is studied. Taking the aquaculture of bighead carp and silver carp as an example, considering the characteristics of the growth and the reproduction of prymnesiacee, and taking prymnesiacee toxin as the pollutant source, a harvesting model of fish aquaculture is built. The finite-time stability of the system is discussed. While the fish aquaculture and the elimination of the algae toxin targeted as pollutant source can be carried out simultaneously, an optimal harvesting method is made by the Pontryagin maximum principle, from which a general algorithm of the optimal harvesting solution can be obtained. The stimulation shows the effectiveness of the result.

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• Asia-Pacific — Scientists call for bolder actions to protect coral reefs
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SK channels are responsible for long-lasting hyperpolarization following action potential and contribute to the neuronal integration signal. This study evaluates the involvement of SK channels on learning and memory in rats, by comparing the effects of two SK channel blockers, i.e., apamin which recognizes SK2 and SK3 channels, and lei-Dab7 which binds SK2 channels only. lei-Dab7 totally competes and contests apamin binding on whole brain sections (IC₅₀: 11.4 nM). Using an olfactory associative task, intracerebroventricular blocker injections were tested on reference memory. Once the task was mastered with one odor pair, it was then tested with a new odor pair. Apamin (0.3 ng), injected before or after the acquisition session, improved new odor pair learning in a retention session 24 hours later, whereas lei-Dab7 (3 ng) did not significantly affect the mnesic processes. These results indicated that the blockage of SK channels by apamin facilitates consolidation on new odor associations; lei-Dab7, containing only SK2 subunits, remains without effect suggesting an involvement of SK3 channels in the modulation of the mnesic processes.

As essential conservative component of the innate immune systems of living organisms, antimicrobial peptides (AMPs) could complement pharmaceuticals that increasingly fail to combat various pathogens exhibiting increased resistance to microbial antibiotics. Among the properties of AMPs that suggest their potential as therapeutic agents, diverse peptides in the venoms of various predators demonstrate antimicrobial activity and kill a wide range of microorganisms. To identify potent AMPs, the study reported here involved a transcriptomic profiling of the tentacle secretion of the sea anemone Cnidopus japonicus. An in silico search algorithm designed to discover toxin-like proteins containing AMPs was developed based on the evaluation of the properties and structural peculiarities of amino acid sequences. The algorithm revealed new proteins of the anemone containing antimicrobial candidate sequences, and 10 AMPs verified using high-throughput proteomics were synthesized. The antimicrobial activity of the candidate molecules was experimentally estimated against Gram-positive and -negative bacteria. Ultimately, three peptides exhibited antimicrobial activity against bacterial strains, which suggests that the method can be applied to reveal new AMPs in the venoms of other predators as well.

A mathematical model describing the dynamics of toxin producing phytoplankton–zooplankton interaction with instantaneous nutrient recycling is proposed. We have explored the dynamics of plankton ecosystem with multiple delays; one due to gestation period in the growth of phytoplankton population and second due to the delay in toxin liberated by TPP. It is established that a sequence of Hopf bifurcations occurs at the interior equilibrium as the delay increases through its critical value. The direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions are determined using the theory of normal form and center manifold. Meanwhile, effect of toxin on the stability of delayed plankton system is also established numerically. Finally, numerical simulations are carried out to support and supplement the analytical findings.

A simple model of phytoplankton-zooplankton interaction with a periodic input nutrient is presented. The model is then used to study a nutrient-plankton interaction with a toxic substance that inhibits the growth rate of phytoplankton. The effects of the toxin upon the existence, magnitude, and stability of the periodic solutions are discussed.

This paper deals with a nutrient-phytoplankton-zooplankton ecosystem model consisting of dissolved limiting nutrient with nutrient uptake functions. We use a Holling type-II harvest function to model density dependent plankton population. It is assumed that phytoplankton release toxic chemical for self defense against their predators. The model system is studied analytically and the threshold conditions for the existence and stability of various steady states are worked out. It is observed that if the rate of toxin produced by phytoplankton population crosses a certain critical value, the system enters into Hopf bifurcation. We have derived the direction of Hopf-bifurcation. Our observations indicate that constant nutrient input and the maximal zooplankton conversion rate influence the nutrient-plankton ecosystem model and maintain stability around the coexistence equilibrium in the presence of toxic chemical release by phytoplankton for self defense. It is observed that harvesting rates of the plankton population play a vital role in changing the stability criteria. Computer simulations have been carried out to illustrate different analytical results.