The colouration of the venomous coral snakes (family Elapidae) and their mimics (families Aniliidae and Golubridae)

The bright coloured, highly venomous coral snakes, Leptomicrurus, Micrurus and Micruroides (family Elapidae) and a series of harmless or mildly toxic mimics form an important component of the snake fauna of the Americas. Coral snake patterns are defined as any dorsal pattern found in any species of venomous coral snake and/or any dorsal pattern containing a substantial amount of red, pink or orange distributed so as to resemble that of some species of venomous coral snake. The components of coral snake colouration are described and four principal dorsal patterns are recognized: unicolour, bicolour, tricolour and quadricolour. The tricolour patterns may be further clustered based on the number of black bands or rings separating the red ones as: monads, dyads, triads, tetrads or pentads. A detailed classification of all coral snake colour patterns is presented and each pattern is illustrated. The taxonomic distribution of these patterns is surveyed for mimics and the 56 species of highly venomous coral snakes. Among the latter, the most frequent encountered patterns are tricolour monads, tricolour triads and bicolour rings, in that order. No venomous coral snakes have a tricolour dyad, tricolour tetrad or quadricolour pattern. As many as 115 species of harmless or mildly toxic species, c. 18% of all American snakes, are regarded as coral snake mimics. The colouration and behavioural traits of venomous coral snakes combine to form a significant antipredator defence of an aposematic type. The mimics in turn receive protection from predators that innately or through learning avoid coral snake colour patterns. The precise resemblances in colouration between sympatric non-coral snakes and venomous coral snakes and the concordant geographic variation between the two strongly support this view. Batesian mimicry with the highly venomous coral snakes as the models and the other forms as the mimics is the favoured explanation for this situation. It is further concluded that a number of species in the genera Elaphe, Farancia, Nerodia and Thamnophis, although having red in their colouration, should not be included in the coral snake mimic guild.     

Sequence-specific base pair mimics are efficient topoisomerase IB inhibitors

Topoisomerase IB controls DNA topology by cleaving DNA transiently. This property is used by inhibitors, such as camptothecin, that stabilize, by inhibiting the religation step, the cleavage complex, in which the enzyme is covalently attached to the 3'-phosphate of the cleaved DNA strand. These drugs are used in clinics as antitumor agents. Because three-dimensional structural studies have shown that camptothecin derivatives act as base pair mimics and intercalate between two base pairs in the ternary DNA-topoisomerase-inhibitor complex, we hypothesized that base pairs mimics could act like campthotecin and inhibit the religation reaction after the formation of the topoisomerase I-DNA cleavage complex. We show here that three base pair mimics, nucleobases analogues of the aminophenyl-thiazole family, once targeted specifically to a DNA sequence were potent topoisomerase IB inhibitors. The targeting was achieved through covalent linkage to a sequence-specific DNA ligand, a triplex-forming oligonucleotide, and was necessary to position and keep the nucleobase analogue in the cleavage complex. In the absence of triplex formation, only a weak binding to the DNA and topoisomerase I-mediated DNA cleavage was observed. The three compounds were equally active once conjugated, implying that the intercalation of the nucleobase upon triplex formation is the essential feature for the inhibition activity.     

Male soldier caste larvae are non-aggressive in the polyembryonic wasp Copidosoma floridanum

Polyembryonic wasps are the only parasitoids in which sociality has evolved. Theory implicates both competition and sex ratio manipulation in the evolution of a sterile soldier caste. However, investment in soldiers by males and females is predicted to differ depending upon how offspring are allocated to hosts and the mating system. Here, we compared male and female soldiers in the polyembryonic wasp Copidosoma floridanum. We found that male and female soldiers are morphologically identical. Unlike females, however, male soldiers were non-aggressive towards all competitors. We discuss these results in relation to theory and polyembryonic wasp biology.     

Engineered conformation-dependent VEGF peptide mimics are effective in inhibiting VEGF signaling pathways

Angiogenesis, or formation of new blood vessels, is crucial to cancer tumor growth. Tumor growth, progression, and metastasis are critically influenced by the production of the pro-angiogenic vascular endothelial growth factor (VEGF). Promising anti-angiogenic drugs are currently available; however, their susceptibilities to drug resistance and long term toxicity are serious impediments to their use, thus requiring the development of new therapeutic approaches for safe and effective angiogenic inhibitors. In this work, peptides were designed to mimic the VEGF-binding site to its receptor VEGFR-2. The VEGF conformational peptide mimic, VEGF-P3(CYC), included two artificial cysteine residues, which upon cyclization constrained the peptide in a loop native-like conformation to better mimic the anti-parallel structure of VEGF. The engineered cyclic VEGF mimic peptide demonstrated the highest affinity to VEGFR-2 by surface plasmon resonance assay. The VEGF peptide mimics were evaluated as inhibitors in several in vitro assays in which VEGF-dependent signaling pathways were observed. All VEGF mimics inhibited VEGFR-2 phosphorylation with VEGF-P3(CYC) showing the highest inhibitory effects when compared with unstructured peptides. Additionally, we show in several angiogenic in vitro assays that all the VEGF mimics inhibited endothelial cell proliferation, migration, and network formation with the conformational VEGF-P3 (CYC) being the best. The VEGF-P3(CYC) also caused a significant delay in tumor development in a transgenic model of VEGF(+/-)Neu2-5(+/-). These results indicate that the structure-based design is important for the development of this peptidomimetic and for its anti-angiogenic effects.     

The functional significance of colouration in cetaceans

Cetaceans show many of the classic mammalian colouration patterns, such as uniform colouration, countershading, and prominent patches of colour, all within one relatively small taxon. We collated all the functional hypotheses for cetacean colouration that have been put forward in the literature and systematically tested them using comparative phylogenetic analyses. We found that countershading is a mechanism by which smaller cetacean species may avoid being seen by their prey. We discovered that prominent markings are associated with group living, fast swimming, and ostentatious behaviour at the surface, suggesting that they function in intraspecific communication. White markings on several parts of the body seem to be involved in the capture of fish, squid, and krill. Therefore, several different selection pressures have shaped the great diversity of skin colouration seen in extant cetaceans, although background matching, disruptive colouration and interspecific communication do not appear to be involved.     

Mastoparan, a peptide toxin from wasp venom, mimics receptors by activating GTP-binding regulatory proteins (G proteins)

Mastoparan, a peptide toxin from wasp venom, is a nonspecific secretagogue. We show here that mastoparan increases the GTPase activity and the rate of nucleotide binding of several purified GTP-binding regulatory proteins (G proteins) whose function is to couple cell-surface receptors to intracellular mediators. Mastoparan accelerated guanosine-5'-(3-O-thiotriphosphate binding and consequent G protein activation in part by promoting the dissociation of bound GDP, the mechanism by which receptors regulate G proteins. ADP-ribosylation by pertussis toxin, which uncouples receptors from G proteins, selectively inhibited mastoparan-stimulated activation. Like receptors, mastoparan was more potent if the G protein was reconstituted in phospholipid vesicles and was active at micromolar concentrations of Mg2+. The structure of mastoparan in a lipid bilayer is similar to that predicted for a cationic intracellular loop of G protein-coupled receptors. Mastoparan thus displays a novel mode of toxicity by acting directly on G proteins to mimic the role normally played by agonist-liganded receptors.     

Laccases for enzymatic colouration of unbleached cotton

The concept presented in this paper is the utilisation of the natural flavonoids present in cotton as anchors to attach other phenolic compounds to the fiber surface. Laccase can catalyze the oxidation of flavonoids in solution producing quinones that can be further polymerised and grafted onto surface of the cotton providing yellow to brown colouration, depending on the external flavonoids used and on the reaction conditions. Factors such as temperature, time of reaction, pretreatment of cotton, mechanical agitation and the role of an organic solvent were studied in order to improve this laccase colouration reaction. After dyeing, colour measurements and fastness tests (washing, friction and weathering fastness) were performed. A strong mechanical agitation, an increased reaction temperature (from 30 to 50 °C), and the addition of an organic solvent improved dyeing.

The natural flavonoids present on cotton were found to play an important role on the grafting reaction, improving dyeing and colour fastness. Since the traditional bleaching pretreatment of cotton removes these natural flavonoids from cotton, the proposed laccase colouration reaction could be carried out without a previous bleaching treatment resulting in a more environmentally friendly process.     

High prevalence of cataracts in birds with pheomelanin-based colouration

The crystalline lens of the eyes of vertebrates focuses light on the retina. Therefore, maintaining the lens clear is necessary for proper visual function. However, oxidative damage to proteins of the lens leads to opacification and lens dysfunction, termed cataract. Antioxidants thus have a role in avoiding the development of cataracts through their reduction of oxidative stress, and glutathione (GSH), a key intracellular antioxidant, belongs to the primary antioxidant defence mechanism of the lens. Other physiological mechanisms that require GSH may compete with the antioxidant mechanism of the eye. Pheomelanin is a main type of melanin, the most common pigment in vertebrates, and its synthesis consumes GSH. Here, we use data on 81 bird species to test the hypothesis that species producing large amounts of pheomelanin should have diminished capacity to use GSH to protect their eyes and, as a consequence, higher prevalence of cataracts. As predicted, the proportion of pheomelanic plumage was positively associated with the proportion of individuals with cataracts across species, suggesting that production of pheomelanin may have profound fitness consequences, as birds with cataracts have limited ability to perform vital activities. This constitutes the first comparative study of cataracts in wild animals.     

Hoverflies (Diptera,Syrphidae) in Agrolandscapes of St. Petersburg and Leningrad Province

A total of 57 species from 32 genera of hoverflies (Diptera, Syrphidae) were found in the agricultural landscapes of St. Petersburg and Leningrad Province. One species, Cheilosia vulpina (Mg.), was recorded in the region for the first time. The largest numbers of species occurred at forest and field edges covered with wild grasses and shrubs, while 21 species of hoverflies were recorded in crops. The species most commonly found in crops were representatives of the genera Melanostoma, Sphaerophoria, and Platycheirus whose larvae feed on aphids.     

The evolution of imperfect mimicry

Examples of imperfect resemblance between Batesian mimics andtheir models appear widespread in the natural world, but sofar few quantitative models have been proposed to explain thephenomenon. I used a simple signal detection model to showthat the relationship between model—mimic similarity and mimic effectiveness is typically nonlinear. In particular, Ifound that there will be little or no further selection toimprove model—mimic resemblance beyond a certain levelif the model species is costly to attack, if the mimic speciesis not particularly profitable (e.g., hard to catch), or ifthe mimic is relatively rare. When there are two different sympatricmodel species, then mimics should usually evolve a phenotypicsimilarity to one or the other model species, but not to both.In contrast, when several model species occur in differentareas (or emerge at different times) and individual mimicsuse each of these areas, then the optimal phenotype should bea "jack-of-all-trades" intermediate phenotype that does notclosely resemble any particular model species. Somewhat surprisingly,the theory predicts that if mimics spend an equal amount oftime with each model species, then the optimal intermediatephenotype should more closely resemble the least numerous andleast noxious model. This phenomenon arises because a vague similarity to an extremely noxious species is usually sufficientto guarantee significant protection, whereas a much closerresemblance to a mildly noxious model species is necessaryto afford a similar level of benefit.     

Aposematic colouration does not explain fear of snakes in humans

Snakes elicit a higher level of fear than other vertebrate animals, yet specific cues responsible for fear of snakes are equivocal. The bright colouration hypothesis suggests that fear responses to snakes are triggered by aposematic colouration, not by snakes per se. We investigated the role of aposematic colouration in fear of snakes in a sample of 10- to 15-year-old Slovak children. Both aposematically and cryptically coloured snakes presented as both colour and black-and-white pictures received higher perceived fear scores than other vertebrates. This suggests that aposematic colouration does not play a crucial role in eliciting fear of snakes. Our results support the snake detection theory suggesting that the human visual system has been influenced by long coexistence between predatory snakes and mammals. As a result, humans have evolved an attentional bias ultimately focused on the correct and rapid detection of these threats.