2,449 research outputs found

    Plasticity facilitates sustainable growth in the commons

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    In the commons, communities whose growth depends on public goods, individuals often rely on surprisingly simple strategies, or heuristics, to decide whether to contribute to the common good (at risk of exploitation by free-riders). Although this appears a limitation, here we show how four heuristics lead to sustainable growth by exploiting specific environmental constraints. The two simplest ones --contribute permanently or switch stochastically between contributing or not-- are first shown to bring sustainability when the public good efficiently promotes growth. If efficiency declines and the commons is structured in small groups, the most effective strategy resides in contributing only when a majority of individuals are also contributors. In contrast, when group size becomes large, the most effective behavior follows a minimal-effort rule: contribute only when it is strictly necessary. Both plastic strategies are observed in natural systems what presents them as fundamental social motifs to successfully manage sustainability

    Species-diagnostic microsatellite loci for the fig wasp genus Pegoscapus

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    To obtain tools for the estimation of inbreeding and assignment of offspring to matrilines, we developed 13 microsatellite loci from the fig wasps that pollinate Ficus obtusifolia. Based on morphological studies, it was thought that a single species (Pegoscapus hoffmeyer) pollinated this fig. However, our data revealed the presence of two coexisting cryptic species. Several diagnostic microsatellite markers may be used to distinguish these two cryptic species. The new microsatellites can be used across a wide range of fig-pollinating wasp species for both evolutionary and population genetic studies

    Patient-Centered Outcomes From Multiparametric MRI and MRI-Guided Biopsy for Prostate Cancer: A Systematic Review.

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    OBJECTIVE: To identify and characterize patient-centered outcomes (PCOs) relating to multiparametric MRI (mpMRI) and MRI-guided biopsy as diagnostic tests for possible prostate cancer. METHODS: Medline via OVID, EMBASE, PsycInfo, and the Cochrane Central register of Controlled Trials (CENTRAL) were searched for relevant articles. Hand searching of reference lists and snowballing techniques were performed. Studies of mpMRI and MRI-guided biopsy that measured any PCO were included. There were no restrictions placed on year of publication, language, or country for study inclusion. All database search hits were screened independently by two reviewers, and data were extracted using a standardized form. RESULTS: Overall, 2,762 database search hits were screened based on title and abstract. Of these, 222 full-text articles were assessed, and 10 studies met the inclusion criteria. There were 2,192 participants featured in the included studies, all of which were conducted in high-income countries. Nineteen different PCOs were measured, with a median of four PCOs per study (range 1-11). Urethral bleeding, pain, and urinary tract infection were the most common outcomes measured. In the four studies that compared mpMRI or MRI-guided biopsy to transrectal ultrasound biopsy, most adverse outcomes occurred less frequently in MRI-related tests. These four studies were assessed as having a low risk of bias. DISCUSSION: PCOs measured in studies of mpMRI or MRI-guided biopsy thus far have mostly been physical outcomes, with some evidence that MRI tests are associated with less frequent adverse outcomes compared with transrectal ultrasound biopsy. There was very little evidence for the effect of mpMRI and MRI-guided biopsy on emotional, cognitive, social, or behavioral outcomes

    Signalling through AMPA receptors on oligodendrocyte precursors promotes myelination by enhancing oligodendrocyte survival

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    Myelin, made by oligodendrocytes, is essential for rapid information transfer in the central nervous system. Oligodendrocyte precursors (OPs) receive glutamatergic synaptic input from axons but how this affects their development is unclear. Murine OPs in white matter express AMPA receptor (AMPAR) subunits GluA2, GluA3 and GluA4. We generated mice in which OPs lack both GluA2 and GluA3, or all three subunits GluA2/3/4, which respectively reduced or abolished AMPAR-mediated input to OPs. In both double- and triple-knockouts OP proliferation and number were unchanged but ~25% fewer oligodendrocytes survived in the subcortical white matter during development. In triple knockouts, this shortfall persisted into adulthood. The oligodendrocyte deficit resulted in ~20% fewer myelin sheaths but the average length, number and thickness of myelin internodes made by individual oligodendrocytes appeared normal. Thus, AMPAR-mediated signalling from active axons stimulates myelin production in developing white matter by enhancing oligodendrocyte survival, without influencing myelin synthesis per se

    Change and Aging Senescence as an adaptation

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    Understanding why we age is a long-lived open problem in evolutionary biology. Aging is prejudicial to the individual and evolutionary forces should prevent it, but many species show signs of senescence as individuals age. Here, I will propose a model for aging based on assumptions that are compatible with evolutionary theory: i) competition is between individuals; ii) there is some degree of locality, so quite often competition will between parents and their progeny; iii) optimal conditions are not stationary, mutation helps each species to keep competitive. When conditions change, a senescent species can drive immortal competitors to extinction. This counter-intuitive result arises from the pruning caused by the death of elder individuals. When there is change and mutation, each generation is slightly better adapted to the new conditions, but some older individuals survive by random chance. Senescence can eliminate those from the genetic pool. Even though individual selection forces always win over group selection ones, it is not exactly the individual that is selected, but its lineage. While senescence damages the individuals and has an evolutionary cost, it has a benefit of its own. It allows each lineage to adapt faster to changing conditions. We age because the world changes.Comment: 19 pages, 4 figure

    Endogenous GABA controls oligodendrocyte lineage cell number, myelination, and CNS internode length

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    Adjusting the thickness and internodal length of the myelin sheath is a mechanism for tuning the conduction velocity of axons to match computational needs. Interactions between oligodendrocyte precursor cells (OPCs) and developing axons regulate the formation of myelin around axons. We now show, using organotypic cerebral cortex slices from mice expressing eGFP in Sox10-positive oligodendrocytes, that endogenously released GABA, acting on GABAA receptors, greatly reduces the number of oligodendrocyte lineage cells. The decrease in oligodendrocyte number correlates with a reduction in the amount of myelination but also an increase in internode length, a parameter previously thought to be set by the axon diameter or to be a property intrinsic to oligodendrocytes. Importantly, while TTX block of neuronal activity had no effect on oligodendrocyte lineage cell number when applied alone, it was able to completely abolish the effect of blocking GABAA receptors, suggesting that control of myelination by endogenous GABA may require a permissive factor to be released from axons. In contrast, block of AMPA/KA receptors had no effect on oligodendrocyte lineage cell number or myelination. These results imply that, during development, GABA can act as a local environmental cue to control myelination and thus influence the conduction velocity of action potentials within the CNS. GLIA 2017;65:309-321

    Parasitic Cape honeybee workers, Apis mellifera capensis, evade policing

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    Relocation of the Cape honeybee, Apis mellifera capensis, by bee-keepers from southern to northern South Africa in 1990 has caused widespread death of managed African honeybee, A. m. scutellata, colonies. Apis mellifera capensis worker bees are able to lay diploid, female eggs without mating by means of automictic thelytoky (meiosis followed by fusion of two meiotic products to restore egg diploidy), whereas workers of other honeybee subspecies are able to lay only haploid, male eggs. The A. m. capensis workers, which are parasitizing and killing A. m. scutellata colonies in northern South Africa, are the asexual offspring of a single, original worker in which the small amount of genetic variation observed is due to crossing over during meiosis (P. Kryger, personal communication). Here we elucidate two principal mechanisms underlying this parasitism. Parasitic A. m. capensis workers activate their ovaries in host colonies that have a queen present (queenright colonies), and they lay eggs that evade being killed by other workers (worker policing)—the normal fate of worker-laid eggs in colonies with a queen. This unique parasitism by workers is an instance in which a society is unable to control the selfish actions of its members

    Evolutionary instability of Zero Determinant strategies demonstrates that winning isn't everything

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    Zero Determinant (ZD) strategies are a new class of probabilistic and conditional strategies that are able to unilaterally set the expected payoff of an opponent in iterated plays of the Prisoner's Dilemma irrespective of the opponent's strategy, or else to set the ratio between a ZD player's and their opponent's expected payoff. Here we show that while ZD strategies are weakly dominant, they are not evolutionarily stable and will instead evolve into less coercive strategies. We show that ZD strategies with an informational advantage over other players that allows them to recognize other ZD strategies can be evolutionarily stable (and able to exploit other players). However, such an advantage is bound to be short-lived as opposing strategies evolve to counteract the recognition.Comment: 14 pages, 4 figures. Change in title (again!) to comply with Nature Communications requirements. To appear in Nature Communication

    Population Dynamics Constrain the Cooperative Evolution of Cross-Feeding

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    Cross-feeding is the exchange of nutrients among species of microbes. It has two potential evolutionary origins, one as an exchange of metabolic wastes or byproducts among species, the other as a form of cooperation known as reciprocal altruism. This paper explores the conditions favoring the origin of cooperative cross-feeding between two species. There is an extensive literature on the evolution of cooperation, and some of the requirements for the evolution of cooperative cross-feeding follow from this prior work–specifically the requirement that interactions be limited to small groups of individuals, such as colonies in a spatially structured environment. Evolution of cooperative cross-feeding by a species also requires that cross-feeding from the partner species already exists, so that the cooperating mutant will automatically be reciprocated for its actions. Beyond these considerations, some unintuitive dynamical constraints apply. In particular, the benefit of cooperative cross-feeding applies only in the range of intermediate cell densities. At low density, resource concentrations are too low to offset the cost of cooperation. At high density, resources shared by both species become limiting, and the two species become competitors. These considerations suggest that the evolution of cooperative cross-feeding in nature may be more challenging than for other types of cooperation. However, the principles identified here may enable the experimental evolution of cross-feeding, as born out by a recent study
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