Mathematical models for estimating fluxes at the sediment-water interface in benthic chamber experiments

Experimental data collected by means of benthic chambers have been used to develop simple mathematical models in order to predict heavy metal and non-metal fluxes at the sediment-water interface. In particular, two mathematical models have been applied to Ba, Co, Fe, Pb, Mn and Cu.Both models estimate benthic fluxes by means of Fick's law but they differ in the modelling of partition between liquid and solid phases. The first model, which is appropriate for Ba and Co, assumes that sorption is the most important process in determining partition. The second model, which gives discrete results for Fe and Pb, assumes that precipitation is the most important process determining the time variation of concentrations. Neither model is suitable to explain experimental data for Mn and Cu.This paper demonstrates the benefit of the use of mathematical models in the interpretation of benthic chambers experiments and in the identification of the relevant processes occurring at the sediment-water interface.     

Becoming a Sign: The Mimic’s Activity in Biological Mimicry

From a semiotic perspective biological mimicry can be described as a tripartite system with a double structure that consists of ecological relations between species and semiotic relations of sign. In this article the focus is on the mimic who is the individual benefiting from its resemblance to the cues or signals of other species or to the environment. In establishing the mimetic resemblance the question of mimic’s activity becomes crucial, and the activity can range from the fixed bodily patterns to fully dynamic behavioural displays. The mimic’s activity can be targeted at two other participants of the mimicry system—either at the model or at the receiver. The first possibility is quite common in camouflage and there are several possibilities for mimic’s activity to occur: selecting a resting place or habitat based on conformity with the environment, changing body coloration to correspond to the surrounding environment, covering oneself with particles of the soil. In its activity aimed at the model, the mimic develops a strong semiotic connection with its specific perceptual environment or part of it and obtains a representational character. In the second possibility the activity of a mimetic organism is aimed at the receiver who is confused by the resemblance, and between the two participants an active communicative interaction is established. Such type of mimicry can be exemplified by abstract threat displays found in various groups of animals, for instance a toad’s upright posture as a response to the presence of a snake. From the semiotic viewpoint it can be interpreted as the motive of fear in the predator’s Umwelt being entered into the mimic’s subjective world and manifested in its behaviour. The mimetic organism ends up in an ambiguous position, where it needs to pretend to be something other than it is. In the final part of the article it is argued that the mimetic sign is basically a false designator as the mimic’s activity to become a sign is aimed at a specific type of signs. Rather than signifying belonging to its own species or group, a mimetic sign indicates that its carrier belongs to the type of some other species. The tension between the form and behaviour of mimetic organisms arises from the discrepancy between the type of organism that it essentially is and the type of organism that the mimetic sign it carries imposes on it.     

Life is more than a computer running DNA software

In his recent interview for the Guardian Craig Venter is elaborating about a household appliance for the future, Digital Biological Converter(DBC). Current prototype, which can produce DNA, is a box attached to the computer which receives DNA sequences over the internet to synthesize DNA; later in future also viruses, proteins, and living cells. This would help the household members to produce, e.g., insulin, virus vaccines or phages that fight antibiotic resistant bacteria. In more distant future, Craig Venter's hope is that the DBC will generate living cells via so-called "Universal Recipient Cell". This platform will allow digitally transformed genomes, downloaded from the internet, to form new cells fitted for the particular needs such as therapeutics, food, fuel or cleaning water. In contrast to this, the authors propose that DNA sequences of genomes do not represent 1:1 depictions of unequivocal coding structures such as genes. In light of the variety of epigenetic markings, DNA can store a multitude of further meanings hidden under the superficial grammar of nucleic acid sequences.     

A mini-review on the effects of COVID-19 on younger individuals

Coronavirus disease 2019 (COVID-19) pandemic has uprooted our lives like never before since its onset in the late December 2019. The world has seen mounting infections and deaths over the past few months despite the unprecedented measures countries are implementing, such as lockdowns, social distancing, mask-wearing, and banning gatherings in large groups. Interestingly, young individuals seem less likely to be impacted by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19. While the rate of transmission, symptom presentation, and fatality is lower in children than people from other age groups, they have been disproportionately affected by strict lockdown measures needed to curb viral spread. In this review, we describe the association between patient age and COVID-19, epidemiology of SARS-CoV-2 infection in children, psychological effects associated with lockdowns and school closures, and possible mechanisms underlying lower transmission rate of COVID-19 in children.     

High levels of multiple metal resistance and its correlation to antibiotic resistance in environmental isolates of Acinetobacter

Forty strains of Acinetobacter were isolated from different environmental sources. All the strains were classified into four genospecies, i.e. A. baumannii (33 isolates), A. calcoaceticus (three isolates), A. junii (three isolates) and A. genospecies3 (one isolate). Susceptibility of these 40 strains to salts of 20 heavy metals and 18 antibiotics was tested by the agar dilution method. All environmental isolates of Acinetobacter were resistant to multiple metal ions (minimum 13 metal ions) while all but one of the strains were resistant to multiple antibiotics (minimum four antibiotics). The maximum number of strains were found to be sensitive to mercury (60% strains) while all strains were resistant to copper, lead, boron and tungsten even at 10 mm concentration. Salts of these four metal ions may be added to the growth medium to facilitate selective isolation of Acinetobacter. Rifampicin and nalidixic acid were the most toxic antibiotics, inhibiting 94.5 and 89.5% of the acinetobacters, respectively. A. genospecies3 was found to be the most resistant species, tolerating high concentrations of all the 20 metal ions and also to a greater number of antibiotics than any other species of Acinetobacter tested. An inhibitory concentration (10 mm) of Ni²⁺ and Zn²⁺ was observed to inhibit the growth of all of the clinical isolates but allowed the growth of the environmental isolates, facilitating the differentiation between pathogenic and non-pathogenic acinetobacters.     

The lunule of caligid copepods: an evolutionarily novel structure

Nearly half of the genera of the family Caligidae possess an evolutionarily novel structure called the “lunule” on the ventral surface of the frontal plate. Lunules are paired cup‐like suckers that assist in securing attachment of the copepod parasite to its host. Although present in genera such as Caligus and Pseudocaligus, lunules are absent in other caligid genera such as Lepeophtheirus as well as in more primitive caligiforms such as members of the families Trebiidae and Dissonidae. We compared the morphology and development of the anterior margin of the frontal plates between two caligids, Pseudocaligus fugu and Lepeophtheirus sekii, and a more basal caligiform, Dissonus heronensis (a dissonid), using scanning electron, transmission electron, and laser confocal microscopes. Our observations suggest that the lunules originated as a modification of the marginal membranes of the ancestral frontal plates. We also demonstrated the presence of an anlagen cell population for the lunule and marginal membrane in the developing frontal plate. These primordial cells can be detected as early as the first stage of the chalimus phase. Based on these observations, an evolutionary scenario for the lunule is proposed based on cytological evidence. This case study enhances our understanding of “evolutionary novelty,” which is a main focus of contemporary evolutionary developmental biology.     

Ion channels in plants: From bioelectricity,via signaling,to behavioral actions

In his recent opus magnum review paper published in the October issue of Physiology Reviews, Rainer Hedrich summarized the field of plant ion channels.¹ He started from the earliest electric recordings initiated by Charles Darwin of carnivorous Dionaea muscipula,^1,2 known as Venus flytrap, and covered the topic extensively up to the most recent discoveries on Shaker-type potassium channels, anion channels of SLAC/SLAH families, and ligand-activated channels of glutamate receptor-like type (GLR) and cyclic nucleotide-gated channels (CNGC).¹