Parallels between sexual strategies and other allocation strategies

Allocation strategies in which a limited resource is apportioned among alternative activities are applicable to diverse structural, genetical and behavioral topics, including male versus female investments. In a model of sex allocation strategies, the absolute fitness of individuals are calculated by summing the production of male and female gametes or offspring, each weighted by its reproductive value. The ESS is obtained by examining the fitness advantage of one phenotype over another. An analogous method is used to obtain a general model of allocation strategies that incorporates some widespread features. Allocation strategies are affected by the sizes and shapes of the reward curves, stochastic factors, and constraints on the allocations permitted. A number of parallels among diverse types of allocation strategies, including the occurrence of fixed, conditional and mixed strategies, and matching rules, are discussed.     

Helical microtubular arrays in onion root hairs

The higher order patterns to which individual plant microtubules contribute are not yet fully described, perhaps because of the problems of reconstructing whole-cell conformations from electron microscope (EM) thin sections. Because microtubules may govern the way in which cellulose microfibrils are deposited in the plant cell wall, it is important to determine the range of permissible conformations for this has implications for the understanding of wall texture. Often, but not always, the EM shows that microtubules occur roughly transversely to the plant cell's long axis and they are usually conceived of as contributing to a series of 'hoops'. However, based on evidence that microtubules can be long relative to the cell's circumference and on the interconnected nature of the cytoskeleton, it was recently proposed that microtubules might be wound helically around the cell; the helical pitch being influenced by the expansion characteristics of the cell. By using whole-cell immunofluorescence and monoclonal antibodies to tubulin, evidence is now presented which confirms that unambiguous helices occur in formaldehyde-fixed onion root hairs.     

Glycerol monoethers in the scent gland secretions of the western diamondback rattlesnake (Crotalus atrox; Serpentes, Crotalinae)

1-O-Monoalkylglycerols with C12 to C20 chains were identified in the scent gland secretions of the western diamondback rattlesnake (Crotalus atrox). This is the first documentation of these compounds in the skin secretions of a reptile.     

The role of the orbitofrontal cortex in the pursuit of happiness and more specific rewards

Cues that reliably predict rewards trigger the thoughts and emotions normally evoked by those rewards. Humans and other animals will work, often quite hard, for these cues. This is termed conditioned reinforcement. The ability to use conditioned reinforcers to guide our behaviour is normally beneficial; however, it can go awry. For example, corporate icons, such as McDonald's Golden Arches, influence consumer behaviour in powerful and sometimes surprising ways, and drug-associated cues trigger relapse to drug seeking in addicts and animals exposed to addictive drugs, even after abstinence or extinction. Yet, despite their prevalence, it is not known how conditioned reinforcers control human or other animal behaviour. One possibility is that they act through the use of the specific rewards they predict; alternatively, they could control behaviour directly by activating emotions that are independent of any specific reward. In other words, the Golden Arches may drive business because they evoke thoughts of hamburgers and fries, or instead, may be effective because they also evoke feelings of hunger or happiness. Moreover, different brain circuits could support conditioned reinforcement mediated by thoughts of specific outcomes versus more general affective information. Here we have attempted to address these questions in rats. Rats were trained to learn that different cues predicted different rewards using specialized conditioning procedures that controlled whether the cues evoked thoughts of specific outcomes or general affective representations common to different outcomes. Subsequently, these rats were given the opportunity to press levers to obtain short and otherwise unrewarded presentations of these cues. We found that rats were willing to work for cues that evoked either outcome-specific or general affective representations. Furthermore the orbitofrontal cortex, a prefrontal region important for adaptive decision-making, was critical for the former but not for the latter form of conditioned reinforcement.     

Rag mutations reveal robust alternative end joining

Mammalian cells repair DNA double-strand breaks (DSBs) through either homologous recombination or non-homologous end joining (NHEJ). V(D)J recombination, a cut-and-paste mechanism for generating diversity in antigen receptors, relies on NHEJ for repairing DSBs introduced by the Rag1-Rag2 protein complex. Animals lacking any of the seven known NHEJ factors are therefore immunodeficient. Nevertheless, DSB repair is not eliminated entirely in these animals: evidence of a third mechanism, 'alternative NHEJ', appears in the form of extremely rare V(D)J junctions and a higher rate of chromosomal translocations. The paucity of these V(D)J events has suggested that alternative NHEJ contributes little to a cell's overall repair capacity, being operative only (and inefficiently) when classical NHEJ fails. Here we find that removing certain portions of murine Rag proteins reveals robust alternative NHEJ activity in NHEJ-deficient cells and some alternative joining activity even in wild-type cells. We propose a two-tier model in which the Rag proteins collaborate with NHEJ factors to preserve genomic integrity during V(D)J recombination.     

A sequence-based variation map of 8.27 million SNPs in inbred mouse strains

A dense map of genetic variation in the laboratory mouse genome will provide insights into the evolutionary history of the species and lead to an improved understanding of the relationship between inter-strain genotypic and phenotypic differences. Here we resequence the genomes of four wild-derived and eleven classical strains. We identify 8.27 million high-quality single nucleotide polymorphisms (SNPs) densely distributed across the genome, and determine the locations of the high (divergent subspecies ancestry) and low (common subspecies ancestry) SNP-rate intervals for every pairwise combination of classical strains. Using these data, we generate a genome-wide haplotype map containing 40,898 segments, each with an average of three distinct ancestral haplotypes. For the haplotypes in the classical strains that are unequivocally assigned ancestry, the genetic contributions of the Mus musculus subspecies--M. m. domesticus, M. m. musculus, M. m. castaneus and the hybrid M. m. molossinus--are 68%, 6%, 3% and 10%, respectively; the remaining 13% of haplotypes are of unknown ancestral origin. The considerable regional redundancy of the SNP data will facilitate imputation of the majority of these genotypes in less-densely typed classical inbred strains to provide a complete view of variation in additional strains.