Bigger is not always better: when brains get smaller

Many studies assume that an increase in brain size is beneficial. However, the costs of producing and maintaining a brain are high, and we argue that brain size should be secondarily reduced by natural selection whenever the costs outweigh the benefits. Our results confirm this by showing that brain size is subject to bidirectional selection. Relative to the ancestral state, brain size in bats has been reduced in fast flyers, while it has increased in manoeuvrable flyers adapted to flight in complex habitats. This study emphasizes that brain reduction and enlargement are equally important, and they should both be considered when investigating brain size evolution.     

Silicon does not always mitigate zinc toxicity in maize

We have investigated the influence of silicon on higher zinc concentration reducing the growth of aboveground parts by ca 50 % in young maize plants (hybrid Novania) grown in hydroponics. Eight different treatments were used: control, Zn (800 μM ZnSO₄·7H₂O), Si1/Si2.5/Si5 (1/2.5/5 mM Na₂SiO₇) and Zn+Si (combination of zinc and all silicon concentrations). The concentration of Zn and Si and their distribution in plants was determined. The growth parameters (length of primary seminal root, leaf area of first and second leaves, fresh and dry weight of below- and above-ground plant parts) of plants grown in various Zn+Si treatments were significantly decreased in comparison to all other treatments. Increasing concentration of Si in combination with Zn treatment and selected hybrid (Novania) resulted in increased physiological stress in comparison to Zn treatment. However, roots and shoots of all Zn+Si treated plants contained significantly lower amount of Zn than Zn treatment. The Si concentration in roots was the same in Si and Zn+Si plants. In general, higher amount of Si was observed in shoots than in roots of Si1- and Si2.5-treated plants and opposite was observed in Si5-treated plants. In spite of significantly decreased root and shoot accumulation of Zn in the presence of Si, no positive effect of Si on Zn toxicity in young maize plants under experimental conditions used in this work and used maize hybrid was observed.     

Warming does not always benefit the small - Results from a plankton experiment

The concern about climate change has re-vitalised the interest in the relationships between body-size of organisms and temperature both at the intraspecific level (James’ rule, Temperature-Size-Rule) and at the interspecific level (Bergmann's rule). In order to test the expected shifts towards smaller body size under warming conditions, a mesocosm experiment using plankton from the Baltic Sea at three temperature levels was performed in April 2010. The hypothesis was tested, that a tendency well established under monoculture conditions, would also be found in phytoplankton embedded in a semi-natural food-web. Six out of seven phytoplankton species abundant enough for analysis did not show the expected shrinkage of cell volume with increasing temperature, while volume shrinkage of the 7th species (Eutreptiella sp.) could be attributed exclusively to the axis which is affected by cell division. Thus it could not be ruled out, that the populations grown at different temperature levels were just at a different stage of the cell cycle. Similarly, we could not find an indication for a replacement of larger species by smaller ones under higher temperature. As a consequence, mean cell size did not respond to temperature. Therefore, we could not support the hypothesis, that warming should benefit the small.     

Local adaptation does not always predict high mating success

The hypothesis that adaptation to local environments can increase mating success was tested using ten replicate lines of Drosophila melanogaster adapted either to 16 °C or to 25 °C. Competitive mating trials at both temperatures were performed with males taken from a pair of lines, one adapted to each temperature. There was no average increase in mating success for males adapted to the local environment. Although one pair of lines showed the expected pattern, another pair showed the reverse pattern. More data are needed on this hypothesis, preferably with lines that have more strongly adapted to local environments.     

Generation of tissue-specific cells from MSC does not require fusion or donor-to-host mitochondrial/membrane transfer

Human mesenchymal stem cells (MSC) hold great promise for cellular replacement therapies. Despite their contributing to phenotypically distinct cells in multiple tissues, controversy remains regarding whether the phenotype switch results from a true differentiation process. Here, we studied the events occurring during the first 120 h after human MSC transplantation into a large animal model. We demonstrate that MSC, shortly after engrafting different tissues, undergo proliferation and rapidly initiate the differentiative process, changing their phenotype into tissue-specific cells. Thus, the final level of tissue-specific cell contribution is not determined solely by the initial level of engraftment of the MSC within that organ, but rather by the proliferative capability of the ensuing tissue-specific cells into which the MSC rapidly differentiate. Furthermore, we show that true differentiation, and not cell fusion or transfer of mitochondria or membrane-derived vesicles between transplanted and resident cells, is the primary mechanism contributing to the change of phenotype of MSC upon transplantation.     

Adaptive foraging does not always lead to more complex food webs

Recent modeling studies exploring the effect of consumers’ adaptivity in diet composition on food web complexity invariably suggest that adaptivity in foraging decisions of consumers makes food webs more complex. That is, it allows for survival of a higher number of species when compared with non-adaptive food webs. Population-dynamical models in these studies share two features: parameters are chosen uniformly for all species, i.e. they are species-independent, and adaptive foraging is described by the search image model. In this article, we relax both these assumptions. Specifically, we allow parameters to vary among the species and consider the diet choice model as an alternative model of adaptive foraging. Our analysis leads to three important predictions. First, for species-independent parameter values for which the search image model demonstrates a significant effect of adaptive foraging on food web complexity, the diet choice model produces no such effect. Second, the effect of adaptive foraging through the search image model attenuates when parameter values cease to be species-independent. Finally, for the diet choice model we observe no (significant) effect of adaptive foraging on food web complexity. All these observations suggest that adaptive foraging does not always lead to more complex food webs. As a corollary, future studies of food web dynamics should pay careful attention to the choice of type of adaptive foraging model as well as of parameter values.     

Why overgrowth of intertidal encrusting algae does not always cause competitive exclusion

Encrusting algae are well-known to be able, for long periods, to withstand shading and overgrowth by other organisms. How this is achieved remains a mystery. It had been proposed that connections with unshaded (non-overgrown) parts of the thallus may allow transfer of nutrients to the shaded part. From this model, I proposed and tested the hypothesis that shaded patches of the intertidal red alga, Hildenbrandia rubra, would survive overgrowth longer, or better, when connected to unshaded thallus than when experimentally separated from surrounding alga. Experimental treatments were shading (black or transparent 80 mm perspex discs or no cover) and scraping (scraped around the disc to remove contacts, a control for effects of scraping, no treatment). The 9 orthogonal combinations of cover and scraping were applied to 3 independent, random replicates (i.e. 27 plots) in each of four randomly chosen sites.

In all 4 sites, over 13 months, shaded H. rubra survived in greater abundance (as % cover) where in contact with surrounding thallus. In one site, there was no effect of shading unless the thallus was isolated. In two sites, shading reduced cover, but was more deleterious where the thallus was isolated. In the fourth site, there were artefacts due to a perspex cover, but still less cover of alga where it was isolated.

This encrusting alga can withstand a long period of complete shading, provided there is connection to unshaded thallus. Interpreting or predicting overgrowth interactions in terms of competitive outcomes is therefore dependent on consideration of whether the overgrown species is actually being affected. It also depends on the duration of overgrowth and, as shown here, the extent to which connectivity with unshaded thallus is effective at preventing or reducing any consequences. Observations and experiments that do not ascertain these are difficult to interpret.     

Wolbachia modification of sperm does not always require residence within developing sperm

Wolbachia are maternally inherited intracellular bacteria known to manipulate the reproduction of their arthropod hosts. Wolbachia commonly affect the sperm of infected arthropods. Wolbachia-modified sperm cannot successfully fertilize unless the female is infected with the same Wolbachia type. A study of spermatogenesis in the parasitic wasp Nasonia vitripennis reveals that Wolbachia are not required in individual spermatocytes or spermatids to modify sperm. In N. vitripennis, Wolbachia modify nearly all sperm, but are found only in approximately 28% of developing sperm, and are also found in surrounding cyst and sheath cells. In the beetle Chelymorpha alternans, Wolbachia can modify up to 90% of sperm, but were never observed within the developing sperm or within the surrounding cyst cells; they were abundant within the outer testis sheath. We conclude that the residence within a developing sperm is not a prerequisite for Wolbachia-induced sperm modification, suggesting that Wolbachia modification of sperm may occur across multiple tissue membranes or act upstream of spermiogenesis.     

Hematopoiesis: how does it happen?

Hematopoiesis entails the generation of stem cells, the proliferation and maintenance of multipotential progenitors, and lineage commitment and maturation. During the past year, critical components of these steps have been defined. Notable are gene-targeting experiments in mice in which one or more hematopoietic lineages have been shown to be ablated upon inactivation of several nuclear regulatory proteins (GATA-2, Tal-1/SCL, Rbtn2/LMO2, PU.1, Ikaros, E2A, and Pax-5), and experiments that establish GATA-1 as a factor capable of programming at least three lineages (erythroid, thrombocytic, and eosinophilic) from a transformed avian progenitor cell.     

Why preferential hydration does not always stabilize the native structure of globular proteins

The observed preferential hydration of proteins in aqueous MgCl2 solutions at low pH and low salt concentration (Arakawa et al., 1990) prompted a scrutiny of possible protein stabilization by MgCl2 under the same conditions, in view of earlier observations in aqueous solutions of sugars, amino acids, and a number of salts that preferential hydration is usually accompanied by the stabilization of the native structure of globular proteins. The results of thermal transition experiments on five proteins (ribonuclease A, lysozyme, beta-lactoglobulin, chymotrypsinogen, and bovine serum albumin) revealed neither significant stabilization nor destabilization of the protein structures by MgCl2 both at acid conditions (except for ribonuclease A, which was stabilized, but to a much smaller extent than by MgSO4) and at higher pH at which MgCl2 displayed little preferential hydration. This was in contrast to the great stabilizing action of MgSO4 at the same conditions. 2-Methyl-2,4-pentanediol (MPD), which gives a very large preferential hydration of native ribonuclease A at pH 5.8 [Pittz & Timasheff (1978) Biochemistry 17, 615-623], was found to be a strong destabilizer of that protein at the same conditions. Analysis of the preferentially hydrating solvent systems led to their classification into two categories: those in which the preferential hydration is independent of solution conditions and those in which it varies with conditions. The first always stabilize protein structure, while the second do not. In the first category the predominant interaction is that of cosolvent exclusion, determined by solvent properties, with the protein being essentially inert. In the second category interactions are determined to a major extent by the chemical nature of the protein surface.(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlation between glycosyl torsion angle and sugar ring pucker does not always exist.

A survey of the conformational parameters of deoxypyrimidine nucleosides and nucleotides shows that the correlation between glycosyl torsion angle and sugar pucker, which has often been considered to be well-established, does not always exist. This may be of significance when interactions between DNA and other molecules are considered.     

Major histocompatibility complex similarity and sexual selection: different does not always mean attractive

Females that mate multiply have the possibility to exert postcopulatory choice and select more compatible sperm to fertilize eggs. Prior work suggests that dissimilarity in major histocompatibility complex (MHC) plays an important role in determining genetic compatibility between partners. Favouring a partner with dissimilar MHC alleles would result in offspring with high MHC diversity and therefore with enhanced survival thanks to increased resistance to pathogens and parasites. The high variability of MHC genes may further allow discrimination against the sperm from related males, reducing offspring homozygosity and inbreeding risk. Despite the large body of work conducted at precopulatory level, the role of MHC similarity between partners at postcopulatory level has been rarely investigated. We used an internal fertilizing fish with high level of multiple matings (Poecilia reticulata) to study whether MHC similarity plays a role in determining the outcome of fertilization when sperm from two males compete for the same set of eggs. We also controlled for genomewide similarity by determining similarity at 10 microsatellite loci. Contrary to prediction, we found that the more MHC‐similar male sired more offspring while similarity at the microsatellite loci did not predict the outcome of sperm competition. Our results suggest that MHC discrimination may be involved in avoidance of hybridization or outbreeding rather than inbreeding avoidance. This, coupled with similar findings in salmon, suggests that the preference for MHC‐dissimilar mates is far from being unanimous and that pre‐ and postcopulatory episodes of sexual selection can indeed act in opposite directions.     

Legumes tolerance to rhizobia is not always observed and not always deserved

Rhizobia display dual lifestyle. These bacteria are soil inhabitants but can also elicit the formation of a special niche on the root of legume plants, the nodules. In such organs, rhizobia can promote the growth of their host by providing them nitrogen they captured from atmosphere. All along the infection process, the plant innate immunity has to be controlled to maintain compatible interaction. However, nodulation does not always result in profit for the plant as compatible interactions include both nitrogen‐fixing and non‐fixing associations. In recent years, our knowledge on the mechanisms involved in the control of plant innate immunity during rhizobia‐legume interactions has greatly improved notably by the identification of bacterial and plant genes activating or suppressing the plant defences. Surprisingly, results also demonstrated that in some cases, plant defence reactions result in abortion of the nodulation process despite that the rhizobial strain has all the genetic potential to establish mutualism. In such situation, experimental evolution approaches highlighted possible rapid switches of incompatible rhizobia either to mutualistic or parasitic behaviour. Here, we review this recent literature.     

Genetic evidence does not support an etruscan origin in Anatolia

The debate on the origins of Etruscans, documented in central Italy between the eighth century BC and the first century AD, dates back to antiquity. Herodotus described them as a group of immigrants from Lydia, in Western Anatolia, whereas for Dionysius of Halicarnassus they were an indigenous population. Dionysius' view is shared by most modern archeologists, but the observation of similarities between the (modern) mitochondrial DNAs (mtDNAs) of Turks and Tuscans was interpreted as supporting an Anatolian origin of the Etruscans. However, ancient DNA evidence shows that only some isolates, and not the bulk of the modern Tuscan population, are genetically related to the Etruscans. In this study, we tested alternative models of Etruscan origins by Approximate Bayesian Computation methods, comparing levels of genetic diversity in the mtDNAs of modern and ancient populations with those obtained by millions of computer simulations. The results show that the observed genetic similarities between modern Tuscans and Anatolians cannot be attributed to an immigration wave from the East leading to the onset of the Etruscan culture in Italy. Genetic links between Tuscany and Anatolia do exist, but date back to a remote stage of prehistory, possibly but not necessarily to the spread of farmers during the Neolithic period. Am J Phys Anthropol 152:11–18, 2013. © 2013 Wiley Periodicals, Inc.