Social Neuroscience: More Friends,More Problems…More Gray Matter?

The social brain hypothesis generically posits that increasing social group size relates is associated with an increase in neocortex size. A new study identifies, within a species, the specific neural circuit that may confer the primate ability to manage social relationships as they increase in number.     

More genes in vertebrates?

With the acquisition of complete genome sequences from several animals, there is renewed interest in the pattern of genome evolution on our own lineage. One key question is whether gene number increased during chordate or vertebrate evolution. It is argued here that comparing the total number of genes between a fly, a nematode and human is not appropriate to address this question. Extensive gene loss after duplication is one complication; another is the problem of comparing taxa that are phylogenetically very distant. Amphioxus and tunicates are more appropriate animals for comparison to vertebrates. Comparisons of clustered homeobox genes, where gene loss can be identified, reveals a one to four mode of evolution for Hox and ParaHox genes. Analyses of other gene families in amphioxus and vertebrates confirm that gene duplication was very widespread on the vertebrate lineage. These data confirm that vertebrates have more genes than their closest invertebrate relatives, acquired through gene duplication. abbreviations IHGSC, International Human Genome Sequencing Consortium; TCESC, The C. elegans Sequencing Consortium.     

More genes in fish?

Certain species of fish have recently become important model systems in comparative genomics and in developmental biology, in certain instances because of their small genome sizes (e.g., in the pufferfish) and, in other cases, because of the opportunity they provide to combine an easily accessible and experimentally manipulable embryology with the power of genetic approaches (e.g., in the zebrafish). The resulting accumulation of genomic information indicates that, surprisingly, many gene families of fish consist of more members than in mammals. Most modern fish, including the zebrafish and medakka, are diploid organisms; however, the greater number of genes in fish was possibly caused by additional ancient genome duplications which happened in the lineage leading to modern ray-finned fishes but not along the lineage leading to tetrapods. Since these two lineages shared their last common ancestor (in the Devonian about 360 million years ago) individual duplicated members of gene families were later lost in fish. Interestingly, comparative data indicate that, in some cases, genes in mammals even serve somewhat different functions than their homologues in fish, highlighting that the degree of evolutionary relatedness of genes is not always a reliable predictor of their evolutionary conservation and their similarity of function. Since fish are phenotypically probably not more complex than mammals, it is possible that evolution took alternative paths to the “economics of genomics” through alternative solutions to gene regulation. It is suggested that the more complex genomic architecture of fish permitted them to adapt and speciate quickly in response to changing selective regimes. BioEssays 20 :511–515, 1998. © 1998 John Wiley & Sons, Inc.     

More plastids in human parasites?

Trypanosomatid parasites are disease agents with an extraordinarily broad host range including humans, livestock and plants. Recent work has revealed that trypanosomatids harbour numerous genes sharing apparent common ancestry with plants and/or bacteria. Although there is no evidence of a plastid (chloroplast-like organelle) in trypanosomatids, the presence of such genes suggests lateral gene transfer from some photosynthetic organism(s) during trypanosomatid evolution. Remarkably, many products of these horizontally acquired genes now function in the glycosome, a highly modified peroxisome unique to trypanosomatids and their near relatives.     

More Status or More Children? Social Status,Fertility Reduction,and Long-Term Fitness

A model is presented that shows that reduced fertility in humans can be explained as part of an evolved strategy to maximize long-term fitness in the face of periodic calamities that result in demographic crashes. Three conditions must be met for this model to be plausible: (1) human population history has been characterized by local periods of growth punctuated by recurrent crashes caused by calamities such as climatically induced resource shortfalls; (2) a strategy is available to individuals that increases the probability of survival through a crash, but that, to implement, requires diverting resources away from producing more offspring; and (3) long-term fitness benefits to increased survivorship through a crisis must outweigh or equal the fitness benefits that would accrue to putting the same resources into higher fertility. We present a model that shows that increases in survivorship can outweigh the benefits of higher fertility even if crises are neither very frequent nor particularly severe.     

Plant-endophyte-herbivore interactions: More than just alkaloids?

A recent paper by Rasmussen et al., (New Phytol 2007; 173:787–97) describes the interactions between Lolium perenne cultivars with contrasting carbohydrate content and the symbiotic fungal endophyte Neotyphodium lolii at different levels of nitrogen supply. In a subsequent study undertaken by Rasmussen et al., (Plant Physiol 2008; 146:1440–53) 66 metabolic variables were analysed in the same material, revealing widespread effects of endophyte infection, N supply and cultivar carbohydrate content on both primary and secondary metabolites. Here, we link insect numerical responses to these metabolic responses using multiple regression analysis.Key words: Neotyphodium lolii, Lolium perenne, high sugar grasses, metabolomics, insect herbivoresPasture grasses are often infected with symbiotic fungal endophytes and benefits for host plants arising out of these associations are generally ascribed to endophyte produced anti-herbivorous alkaloids. We tested the effects of (i) infection with three strains of endophytes differing in their alkaloid profiles, (ii) high vs. low nitrogen (N) supply, and (iii) ryegrass cultivars with high vs. control levels of water soluble carbohydrates (WSCs) on numerical insect responses (aphids, thrips, mites). A difference in WSC content between the cultivars had no significant effect on insect numbers, whereas high N compared to low N supply increased mites, thrips and alate Rhopalosiphum spp., but decreased apterous Rhopalosiphum spp. The effect of endophyte infection was strain dependant and differed for the different insects.A total of 66 metabolic variables of the same plants analysed prior to insect treatment were linked to insect responses using multiple regression analysis. One of the major conclusions to be drawn is that alkaloids are not always the most important factor influencing numerical insect responses which will also be determined by other metabolites, clearly indicating the importance of metabolomics type studies to point the way toward a mechanistic explanation of grass-endophyte-herbivore interactions.Grass species are often hosts of symbiotic clavicipitaceous endophytic fungi¹ residing in the apoplastic spaces of above ground plant parts and usually not causing any visible symptoms of infection.^2–4 These fungal symbionts confer protection from insect herbivory to their host plants through alkaloids,^5–8 some of which (ergovaline, lolitrem B) are also toxic to grazing mammals.^9,10 Natural endophyte strains lacking these mammalian toxins, but still retaining at least some of their insect deterring features, have been commercialized and are now widely used in ryegrass and tall fescue based pastures.^11,12     

A More Efficient Use of Hospital Beds?

Faced with a shortage of trained nursing staff and a high wastage rate among learners the management of a district general hospital decided to close some of its acute beds. A beds committee attempted to minimize the effects of these closures by introducing a bed bureau, “pooling,” and a simple system for forecasting waiting list admissions.The figures for recruitment and wastage of nurses improved, and a very high turnover per available bed was achieved. This increased efficiency in numerical terms was not mirrored by an improvement in the morale of the doctors and nurses working on the wards, who were subjected to new pressures and considered that at times the standard of patient care deteriorated.     

Protein Interaction Networks—More Than Mere Modules

It is widely believed that the modular organization of cellular function is reflected in a modular structure of molecular networks. A common view is that a “module” in a network is a cohesively linked group of nodes, densely connected internally and sparsely interacting with the rest of the network. Many algorithms try to identify functional modules in protein-interaction networks (PIN) by searching for such cohesive groups of proteins. Here, we present an alternative approach independent of any prior definition of what actually constitutes a “module”. In a self-consistent manner, proteins are grouped into “functional roles” if they interact in similar ways with other proteins according to their functional roles. Such grouping may well result in cohesive modules again, but only if the network structure actually supports this. We applied our method to the PIN from the Human Protein Reference Database (HPRD) and found that a representation of the network in terms of cohesive modules, at least on a global scale, does not optimally represent the network''s structure because it focuses on finding independent groups of proteins. In contrast, a decomposition into functional roles is able to depict the structure much better as it also takes into account the interdependencies between roles and even allows groupings based on the absence of interactions between proteins in the same functional role. This, for example, is the case for transmembrane proteins, which could never be recognized as a cohesive group of nodes in a PIN. When mapping experimental methods onto the groups, we identified profound differences in the coverage suggesting that our method is able to capture experimental bias in the data, too. For example yeast-two-hybrid data were highly overrepresented in one particular group. Thus, there is more structure in protein-interaction networks than cohesive modules alone and we believe this finding can significantly improve automated function prediction algorithms.     

Building Ribosomes: Even More Expensive Than Expected?

Recent quantitative analyses of ribosomal protein trafficking in HeLa cells have revealed a prominent and unexpected role for the proteasome in regulating the availability of ribosomal proteins for subunit assembly.     

Do Women Prefer More Complex Music around Ovulation?

The evolutionary origins of music are much debated. One theory holds that the ability to produce complex musical sounds might reflect qualities that are relevant in mate choice contexts and hence, that music is functionally analogous to the sexually-selected acoustic displays of some animals. If so, women may be expected to show heightened preferences for more complex music when they are most fertile. Here, we used computer-generated musical pieces and ovulation predictor kits to test this hypothesis. Our results indicate that women prefer more complex music in general; however, we found no evidence that their preference for more complex music increased around ovulation. Consequently, our findings are not consistent with the hypothesis that a heightened preference/bias in women for more complex music around ovulation could have played a role in the evolution of music. We go on to suggest future studies that could further investigate whether sexual selection played a role in the evolution of this universal aspect of human culture.     

The Genetic Code—More Than Just a Table

The standard codon table is a primary tool for basic understanding of molecular biology. In the minds of many, the table’s orderly arrangement of bases and amino acids is synonymous with the true genetic code, i.e., the biological coding principle itself. However, developments in the field reveal a much more complex and interesting picture. In this article, we review the traditional codon table and its limitations in light of the true complexity of the genetic code. We suggest the codon table be brought up to date and, as a step, we present a novel superposition of the BLOSUM62 matrix and an allowed point mutation matrix. This superposition depicts an important aspect of the true genetic code—its ability to tolerate mutations and mistranslations.