Genome of an arbuscular mycorrhizal fungus provides insight into the oldest plant symbiosis.

The mutualistic symbiosis involving Glomeromycota, a distinctive phylum of early diverging Fungi, is widely hypothesized to have promoted the evolution of land plants during the middle Paleozoic. These arbuscular mycorrhizal fungi (AMF) perform vital functions in the phosphorus cycle that are fundamental to sustainable crop plant productivity. The unusual biological features of AMF have long fascinated evolutionary biologists. The coenocytic hyphae host a community of hundreds of nuclei and reproduce clonally through large multinucleated spores. It has been suggested that the AMF maintain a stable assemblage of several different genomes during the life cycle, but this genomic organization has been questioned. Here we introduce the 153-Mb haploid genome of Rhizophagus irregularis and its repertoire of 28,232 genes. The observed low level of genome polymorphism (0.43 SNP per kb) is not consistent with the occurrence of multiple, highly diverged genomes. The expansion of mating-related genes suggests the existence of cryptic sex-related processes. A comparison of gene categories confirms that R. irregularis is close to the Mucoromycotina. The AMF obligate biotrophy is not explained by genome erosion or any related loss of metabolic complexity in central metabolism, but is marked by a lack of genes encoding plant cell wall-degrading enzymes and of genes involved in toxin and thiamine synthesis. A battery of mycorrhiza-induced secreted proteins is expressed in symbiotic tissues. The present comprehensive repertoire of R. irregularis genes provides a basis for future research on symbiosis-related mechanisms in Glomeromycota.

Nest distribution varies with dispersal method and familiarity-mediated aggression for two sympatric ants

Dispersal mechanisms and competition together play a key role in the spatial distribution of a population. Species that disperse via fission are likely to experience high levels of localized competitive pressure from conspecifics relative to species that disperse in other ways. Although fission dispersal occurs in many species, its ecological and behavioural effects remain unclear. We compared foraging effort, nest spatial distribution and aggression of two sympatric ant species that differ in reproductive dispersal: Streblognathus peetersi, which disperse by group fission, and Plectroctena mandibularis, which disperse by solitary wingless queens. We found that although both species share space and have similar foraging strategies, they differ in nest distribution and aggressive behaviour. The spatial distribution of S. peetersi nests was extremely aggregated, and workers were less aggressive towards conspecifics from nearby nests than towards distant conspecifics and all heterospecific workers. By contrast, the spatial distribution of P. mandibularis nests was overdispersed, and workers were equally aggressive towards conspecific and heterospecific competitors regardless of nest distance. Finally, laboratory experiments showed that familiarity led to the positive relationship between aggression and nest distance in S. peetersi. While unfamiliar individuals were initially aggressive, the level of aggression decreased within 1 h of contact, and continued to decrease over 24 h. Furthermore, individuals from near nests that were not aggressive could be induced to aggression after prolonged isolation. Overall, these results suggest that low aggression mediated by familiarity could provide benefits for a species with fission reproduction and an aggregated spatial distribution.

Pupal cocoons affect sanitary brood care and limit fungal infections in ant colonies.

BACKGROUND: The brood of ants and other social insects is highly susceptible to pathogens, particularly those that penetrate the soft larval and pupal cuticle. We here test whether the presence of a pupal cocoon, which occurs in some ant species but not in others, affects the sanitary brood care and fungal infection patterns after exposure to the entomopathogenic fungus Metarhizium brunneum. We use a) a comparative approach analysing four species with either naked or cocooned pupae and b) a within-species analysis of a single ant species, in which both pupal types co-exist in the same colony. RESULTS: We found that the presence of a cocoon did not compromise fungal pathogen detection by the ants and that species with cocooned pupae increased brood grooming after pathogen exposure. All tested ant species further removed brood from their nests, which was predominantly expressed towards larvae and naked pupae treated with the live fungal pathogen. In contrast, cocooned pupae exposed to live fungus were not removed at higher rates than cocooned pupae exposed to dead fungus or a sham control. Consistent with this, exposure to the live fungus caused high numbers of infections and fungal outgrowth in larvae and naked pupae, but not in cocooned pupae. Moreover, the ants consistently removed the brood prior to fungal outgrowth, ensuring a clean brood chamber. CONCLUSION: Our study suggests that the pupal cocoon has a protective effect against fungal infection, causing an adaptive change in sanitary behaviours by the ants. It further demonstrates that brood removal-originally described for honeybees as "hygienic behaviour"-is a widespread sanitary behaviour in ants, which likely has important implications on disease dynamics in social insect colonies.

Admissions of patients with alcohol intoxication in the Emergency Department: a growing phenomenon.

QUESTION UNDER STUDY: To investigate the change over time in the number of ED admissions with positive blood alcohol concentration (BAC) and to evaluate predictors of BAC level. METHODS: We conducted a single site retrospective study at the ED of a tertiary referral hospital (western part of Switzerland) and obtained all the BAC performed from 2002 to 2011. We determined the proportion of ED admissions with positive BAC (number of positive BAC/number of admissions). Regression models assessed trends in the proportion of admissions with positive BAC and the predictors of BAC level among patients with positive BAC. RESULTS: A total of 319,489 admissions were recorded and 20,021 BAC tests were performed, of which 14,359 were positive, divided 34.5% female and 65.5% male. The mean (SD) age was 41.7(16.8), and the mean BAC was 2.12(1.04) permille (g of ethanol/liter of blood). An increase in the number of positive BAC was observed, from 756 in 2002 to 1,819 in 2011. The total number of admissions also increased but less: 1.2 versus 2.4 times more admissions with positive BAC. Being male was independently associated with a higher (+0.19 permille) BAC, as was each passing year (+0.03). A significant quadratic association with age indicated a maximum BAC at age 53. CONCLUSION: We observed an increase in the percentage of admissions with positive BAC that was not limited to younger individuals. Given the potential consequences of alcohol intoxication, and the large burden imposed on ED teams, communities should be encouraged to take measures aimed at reducing alcohol intoxication.

Convergent genetic architecture underlies social organization in ants.

Complex adaptive polymorphisms are common in nature, but what mechanisms maintain the underlying favorable allelic combinations [1-4]? The convergent evolution of polymorphic social organization in two independent ant species provides a great opportunity to investigate how genomes evolved under parallel selection. Here, we demonstrate that a large, nonrecombining "social chromosome" is associated with social organization in the Alpine silver ant, Formica selysi. This social chromosome shares architectural characteristics with that of the fire ant Solenopsis invicta [2], but the two show no detectable similarity in gene content. The discovery of convergence at two levels-the phenotype and the genetic architecture associated with alternative social forms-points at general genetic mechanisms underlying transitions in social organization. More broadly, our findings are consistent with recent theoretical studies suggesting that suppression of recombination plays a key role in facilitating coordinated shifts in coadapted traits [5, 6].

Blurred pictures from the crime scene: the growing case for a function of Chlamydiales in plastid endosymbiosis.

A number of recent papers have brought suggestive evidence for an active role of Chlamydiales in the establishment of the plastid. Chlamydiales define a very ancient group of obligate intracellular bacterial pathogens that multiply in vesicles within eukaryotic phagotrophic host cells such as animals, amoebae or other protists, possibly including the hypothetical phagotroph that internalized the cyanobacterial ancestor of the plastid over a billion years ago. We briefly survey the case for an active role of these ancient pathogens in plastid endosymbiosis. We argue that a good understanding of the Chlamydiales infection cycle and diversity may help to shed light on the process of metabolic integration of the evolving plastid.