Is UAA or UGA part of the recognition signal for ribosomal initiation?

In none of the 92 published prokaryotic sequences is a translation codon preceeded by UAG as the first "termination codon". In most cases the UAA or UGA is close to the initiation codon and may be part of the ribosome recognition signal.     

Why are behavioral and immune traits linked?

Through behavior, animals interact with a world where parasites abound. It is easy to understand how behavioral traits can thus have a differential effect on pathogen exposure. Harder to understand is why we observe behavioral traits to be linked to immune defense traits. Is variation in immune traits a consequence of behavior-induced variation in immunological experiences? Or is variation in behavioral traits a function of immune capabilities? Is our immune system a much bigger driver of personality than anticipated? In this review, I provide examples of how behavioral and immune traits co-vary. I then explore the different routes linking behavioral and immune traits, emphasizing on the physiological/hormonal mechanisms that could lead to immune control of behavior. Finally, I discuss why we should aim at understanding more about the mechanisms connecting these phenotypic traits.     

Why some parasites are widespread and abundant while others are local and rare?

Abundances and distributions of species are usually associated. This implies that as a species declines in abundance so does the number of sites it occupies. Conversely, when there is an increase in a species' range size, it is usually followed by an increase in population size (Gaston et al. 2000 ). This ecological phenomenon, also known as the abundance–occupancy relationship (AOR), is well documented in several species of animals and plants (Gaston et al. 2000 ) but has been little investigated in parasites. In this issue of Molecular Ecology, Drovetski et al. ( 2014 ) investigated the AOR in avian haemosporidians (vector‐borne blood parasites) using data from four well‐sampled bird communities. In support of the AOR, the research group found that the abundance of parasite cytochrome b lineages (a commonly used proxy for species identification within this group of parasites) was positively linked with the abundance of susceptible avian host species and that the most abundant haemospordian lineages were those with larger ranges. Drovetski et al. ( 2014 ) also found evidence for both hypotheses proposed to explain the AOR in parasites: the trade‐off hypothesis (TOH) and the niche‐breadth hypothesis (NBH). Interestingly, the main predictor of the AOR was the number of susceptible hosts (i.e. number of infected birds) and not the number of host species the parasites were able to exploit.     

Why are proteins O-glycosylated?

The O-linked oligosaccharides of glycoproteins are usually clustered within heavily glycosylated regions of the peptide chain. Steric interactions between carbohydrate and peptide within these clusters induce the peptide core to adopt a stiff and extended conformation and this conformational effect appears to represent a major function of O-glycosylation.     

Why are human newborns so big and fat?

Human newborns and infants have morphological and physiological traits protecting them against hypothermia. These traits are unusual for primates, with some of them rarely seen in other mammals evolving in an African environment. We can include the following: 1.) A non-allometric, bigger size of the newborn, resulting in the decrease of surface to body mass ratio (S/W). 2.) Greater amount of subcutaneous fat tissue (SFT) increasing insulation. 3.) Greater amount of brown fat tissue increasing nonshivering thermogenesis. 4.) Active thermoregulation when sleeping. 5.) Thermal balance moved in the direction of heat conservation in a few months' old babies. I here present a hypothesis that it was the risk of nocturnal hypothermia in open habitats of late Pliocene that was the selective pressure promoting evolutionary emergence of these traits inHomo erectus. The inverse radiation at night in open habitats causes strong gradient of temperatures. In effect the temperatures near the ground (even in the tropics) can be low enough to endanger newborns and infants with hypothermia. If earlyHomo was naked, slept on the ground and if mortality of their babies caused by hypothermia was high, then selection pressures could have promoted those traits protecting infants against the risk of hypothermia. Since the most important traits (1. & 2.) in respect of heat conservation, depend on mother size, it is postulated that they appeared when female body size increased dramatically i.e. duringHomo erectus stage of human phylogeny.     

Why some leaves are anthocyanic and why most anthocyanic leaves are red?

The adaptive significance of leaf reddening, as it occurs during specific developmental stages or after stress, has puzzled biologists for more than a century. Theoretically, the accumulation of a non-photosynthetic pigment competing with chlorophylls for photon capture would impose a photosynthetic cost, which should be paid off by the benefits afforded by anthocyanins under some circumstances. Hence, the proposed hypotheses presume protective functions against excess light, UV-B radiation, reactive oxygen species, water stress (osmoregulation) and herbivory. The existing arguments in favor of an anti-oxidant, anti-UV-B and osmoregulatory role are confounded by the co-occurrence in leaves of other compounds having the same properties, not absorbing visible light, attaining much higher concentrations and, in some cases, having a more appropriate location to fulfill the ascribed functions. Moreover, the excess light hypothesis should take into account that anthocyanins mainly absorb green photons, which are used photosynthetically in deeper cell layers needing less photoprotection. The more ecological, anti-herbivore hypotheses, consider red leaf color as a signal denoting high defensive commitment, as a camouflage obscuring the green reflectance indicative of a healthy leaf and/or as a device undermining the folivorous insects camouflage. The anti-herbivore hypotheses have not been thoroughly tested, yet they are compatible with the known optical preferences of insects and their underlying physiology. Overall, although a multiplicity of potential roles can be argued, the primary role may depend on the reference system, i.e. species, developmental stage or specific biotic and abiotic stressors.     

Why are some microorganisms boring?

Microorganisms from diverse environments actively bore into rocks, contributing significantly to rock weathering. Carbonates are the most common substrate into which they bore, although there are also reports of microbial borings into volcanic glass. One of the most intriguing questions in microbial evolutionary biology is why some microorganisms bore. A variety of possible selection pressures, including nutrient acquisition, protection from UV radiation and predatory grazing could promote boring. None of these pressures is mutually exclusive and many of them could have acted in concert with varying strengths in different environments to favour the development of microorganisms that bore. We suggest that microbial boring might have begun in some environments as a mechanism against entombment by mineralization.     

Why are small males aggressive?

Aggression is ubiquitous in the animal kingdom, whenever the interests of individuals conflict. In contests between animals, the larger opponent is often victorious. However, counter intuitively, an individual that has little chance of winning (generally smaller individuals) sometimes initiates contests. A number of hypotheses have been put forward to explain this behaviour, including the "desperado effect" according to which, the likely losers initiate aggression due to lack of alternative options. An alternative explanation suggested recently is that likely losers attack due to an error in perception: they mistakenly perceive their chances of winning as being greater than they are. We show that explaining the apparently maladaptive aggression initiated by the likely loser can be explained on purely economic grounds, without requiring either the desperado effect or perception errors. Using a game-theoretical model, we show that if smaller individuals can accurately assess their chance of winning, if this chance is less than, but close to, a half, and if resources are scarce (or the contested resource is of relatively low value), they are predicted to be as aggressive as their larger opponents. In addition, when resources are abundant, and small individuals have some chance of winning, they may be more aggressive than their larger opponents, as it may benefit larger individuals to avoid the costs of fighting and seek alternative uncontested resources.     

Why are female birds ornamented?

Sexual selection is now widely accepted as the main evolutionary explanation of extravagant male ornaments. By contrast, ornaments occurring in females have received little attention and often have been considered as nonadaptive, correlated effects of selection on males. However, recent comparative evidence suggests that female ornaments have evolved quite independently of male showiness. Also, new theoretical models predict that both male mate choice and female contest competition will occur under certain circumstances. This is supported by recent experimental studies. Thus, selection acting on females might be a widespread cause of female ornaments.     

Why are dimethyl sulfoxide and dimethyl sulfone such good solvents?

We have carried out B3PW91 and MP2-FC computational studies of dimethyl sulfoxide, (CH₃)₂SO, and dimethyl sulfone, (CH₃)₂SO₂. The objective was to establish quantitatively the basis for their high polarities and boiling points, and their strong solvent powers for a variety of solutes. Natural bond order analyses show that the sulfur–oxygen linkages are not double bonds, as widely believed, but rather are coordinate covalent single S⁺→O⁻ bonds. The calculated electrostatic potentials on the molecular surfaces reveal several strongly positive and negative sites (the former including σ-holes on the sulfurs) through which a variety of simultaneous intermolecular electrostatic interactions can occur. A series of examples is given. In terms of these features the striking properties of dimethyl sulfoxide and dimethyl sulfone, their large dipole moments and dielectric constants, their high boiling points and why they are such good solvents, can readily be understood. Figure Dimers of dimethyl sulfoxide (DMSO; left) and dimethyl sulfone (DMSO2; right) showing O S—O -hole bonding and C H—O hydrogen bonding. Sulfur atoms are yellow, oxygens are red, carbons are gray and hydrogens are white     

Why are some snails visibly polymorphic,and others not?

Work on Cepaea land-snails since 1950 is surveyed, and various explanations for their visible polymorphism, including predator selection, the influence of sunlight and temperature, co-adaptation and linkage disequilibrium, and "area effects", are discussed. All of these can modify the genetic make-up of natural populations in particular circumstances, but none provide a satisfactory answer to the question of why some species are visibly polymorphic whereas others present a uniform external appearance. The likely explanation is that probably all species are genetically heterogeneous at numerous loci, as a result of heterozygote advantage, co-adaptation and other selective factors maintaining the different alleles in equilibrium, which may sometimes have visible effects on the phenotype. If these are positively disadvantageous, selection for epistatic genes will suppress the visible polymorphism, without affecting the underlying genetical heterogeneity, preserved by selection for other non-visible pleiotropic effects of the alleles involved. But this will not happen if the visibly distinct effects of these different allelomorphs are selectively more or less neutral. Many examples of polymorphism, including the so-called 'pseudo'-polymorphism, are therefore essentially non-adaptive so far as their visible manifestation is concerned, being maintained as balanced polymorphism by selection for non-visible pleiotropic effects of the genes involved.