ON THE EVOLUTION OF HARMING AND RECOGNITION IN FINITE PANMICTIC AND INFINITE STRUCTURED POPULATIONS

Natural selection may favor two very different types of social behaviors that have costs in vital rates (fecundity and/or survival) to the actor: helping behaviors, which increase the vital rates of recipients, and harming behaviors, which reduce the vital rates of recipients. Although social evolutionary theory has mainly dealt with helping behaviors, competition for limited resources creates ecological conditions in which an actor may benefit from expressing behaviors that reduce the vital rates of neighbors. This may occur if the reduction in vital rates decreases the intensity of competition experienced by the actor or that experienced by its offspring. Here, we explore the joint evolution of neutral recognition markers and marker-based costly conditional harming whereby actors express harming, conditional on actor and recipient bearing different conspicuous markers. We do so for two complementary demographic scenarios: finite panmictic and infinite structured populations. We find that marker-based conditional harming can evolve under a large range of recombination rates and group sizes under both finite panmictic and infinite structured populations. A direct comparison with results for the evolution of marker-based conditional helping reveals that, if everything else is equal, marker-based conditional harming is often more likely to evolve than marker-based conditional helping.     

A Posterior Centre Establishes and Maintains Polarity of the Caenorhabditis elegans Embryo by a Wnt-Dependent Relay Mechanism

Cellular polarity is a general feature of animal development. However, the mechanisms that establish and maintain polarity in a field of cells or even in the whole embryo remain elusive. Here we provide evidence that in the Caenorhabditis elegans embryo, the descendants of P₁, the posterior blastomere of the 2-cell stage, constitute a polarising centre that orients the cell divisions of most of the embryo. This polarisation depends on a MOM-2/Wnt signal originating from the P₁ descendants. Furthermore, we show that the MOM-2/Wnt signal is transduced from cell to cell by a relay mechanism. Our findings suggest how polarity is first established and then maintained in a field of cells. According to this model, the relay mechanism constantly orients the polarity of all cells towards the polarising centre, thus organising the whole embryo. This model may also apply to other systems such as Drosophila and vertebrates.     

Ozone effects on visible foliar injury and growth of Fagus sylvatica and Viburnum lantana seedlings grown in monoculture or in mixture

Seedlings of Fagus sylvatica (beech) and Viburnum lantana (Viburnum) grown in monoculture and mixture were exposed to ambient and sub-ambient (charcoal-filtered) ozone concentrations in open-top chambers over the course of the 2003 and 2004 growing seasons at the WSL Lattecaldo open-top chamber facility in southern Switzerland. The aim of the study was to determine how the sensitivity to ozone in ambient air of these two species would differ between monocultures and mixtures in terms of growth and visible foliar injury development. Ambient ozone concentrations were consistently higher from the end of April to the middle of October in 2003 than in 2004 with seasonal peaks and means reaching 147 and 50 parts-per-billion (ppb) in 2003 compared to 124 and 40 ppb in 2004. Ambient AOT40 (ozone concentration accumulated over a threshold of 40 ppb during daylight hours with global radiation >50 W m^?2) values from the end of April to the middle of October reached 48.3 and 26.8 parts-per-billon hours (ppm h) in 2003 and 2004, respectively. In general, Viburnum was a stronger competitor than beech over the course of this 2-year study. Seedlings of Viburnum benefited from interspecific competition in terms of both height growth and above-ground biomass accumulation at the expense of beech seedlings, which showed significantly reduced growth in the mixture as compared to the monoculture. However, as this was only the case for Viburnum growing in the charcoal-filtered treatment, ozone seemed to counteract the beneficial effect of interspecific competition on above-ground biomass accumulation in Viburnum, while at the same time decreasing relative biomass allocation to roots. Foliar sensitivity of the two species was also altered under interspecific competition suggesting that results based on seedlings of single species grown in monocultures may significantly over- or under-estimate foliar sensitivity to ozone. These results demonstrate that competition is an important factor affecting plant responses to ozone stress, but the direction and severity of these effects depend on the interacting species.     

Viral-mediated activation and inhibition of programmed cell death

Viruses are ubiquitous intracellular genetic parasites that heavily rely on the infected cell to complete their replication life cycle. This dependency on the host machinery forces viruses to modulate a variety of cellular processes including cell survival and cell death. Viruses are known to activate and block almost all types of programmed cell death (PCD) known so far. Modulating PCD in infected hosts has a variety of direct and indirect effects on viral pathogenesis and antiviral immunity. The mechanisms leading to apoptosis following virus infection is widely studied, but several modalities of PCD, including necroptosis, pyroptosis, ferroptosis, and paraptosis, are relatively understudied. In this review, we cover the mechanisms by which viruses activate and inhibit PCDs and suggest perspectives on how these affect viral pathogenesis and immunity.     

Running demands and activity profile of men’s rugby sevens: a tournament scenario

This study profiled the changes in running performances and collisions within a Rugby sevens tournament. Sixteen male players were equipped with global positioning system units while competing at the 2015 and 2016 Asia Rugby Sevens series held in Colombo and Hong Kong, respectively. Both tournaments consisted of 4 matches each, and were played over 2 days (i.e., 2 matches/day). Total distance (TD) covered increased in match 3 compared with matches 1 (19 ± 19%; p < 0.001) and 2 (16 ± 11%; p = 0.001), whilst a decrease in TD in match 4 compared with match 3 (8 ± 9%; p = 0.019) was observed. Distances covered within 6.1–12 km·h^-1 and 12.1–14 km·h^-1 speed bands were generally higher in matches 3 and/or 4 when compared with match 1 and/or 2 (p < 0.05). Frequency of entries into 14.1–18 km·h^-1 speed zone was decreased in match 4 compared with match 3 (45 ± 41%; p = 0.009), whilst incidences of heavy, very heavy and severe collisions were generally higher in matches 3 or 4 compared with matches 1 or 2 (p < 0.05). In conclusion, while some decrements in the final match were evident, running performance were generally maintained throughout despite the competitive and congested nature of Rugby Sevens tournaments