Plant species richness and community productivity: why the mechanism that promotes coexistence matters

This paper stresses that the mechanism of coexistence is the key to understanding the relationship between species richness and community productivity. Using model plant communities, we explored two general kinds of mechanisms based on resource heterogeneity and recruitment limitation, with and without any trade-off between reproductive and competitive abilities. We generated different levels of species richness by changing model parameters, in particular the number of species in the regional pool, the degree of recruitment limitation, and the level of heterogeneity. Different diversity–productivity patterns are obtained with different coexistence mechanisms, indicating there is no reason to expect any general relationship between species richness and productivity. We discuss these results in the context of the within-site and across-site aspects of the relationship between species richness and productivity. Furthermore, we extend these results to hypothesize the relationship between species richness and productivity for other coexistence mechanisms not explicitly considered here.     

Role of silk threads in the dispersal of larvae through stream pools

The slow flow found in stream pools should lead to increased larval deposition in habitat unsuitable to many benthic invertebrates such as the larvae of the black fly Simulium tribulatum . To increase their chances of successfully transiting a pool, these larvae may use silk threads previously thought to facilitate settlement in fast-flowing habitat. In this study, we tested two ways in which these threads can affect a larva's transport in slow flow. First, a significant decrease in the fall velocity, which should lead to increased drift distance, was found between live (with silk) and dead (without silk) larvae falling in a laboratory chamber. The reduction due to the presence of silk varied over the natural range of larval sizes from a maximum of a 36% reduction for neonates to only 14% for the largest late-instar larvae. A second possible role of silk, that of increasing the chance of resuspension in slow flow due to increased drag forces, was tested using dynamically scaled models of neonate and late-instar larvae. The coefficient of drag ( C _d) was determined for both model types, with and without scaled silk threads, under conditions recreating a range of naturally occurring Reynolds numbers ( Re ). A significant increase in C _d was found due to the presence of silk for both life stages across relevant ranges in Re . The results of this study show that the presence of silk threads should significantly increase the distance larvae travel and their chances of being resuspended should they be deposited on the bed of a pool. Further, the same threads may act to both limit transport in regions of preferred fast flow, while maximizing transport through regions of unsuitably slow flow.     

Functional characterization and expression analysis of a glutathione transporter, BjGT1, from Brassica juncea: evidence for regulation by heavy metal exposure

Glutathione and its derivatives play an important role in the tolerance of plants against heavy metals. A glutathione transporter, BjGT1 (AJ561120), was cloned and functionally characterized from Brassica juncea, a plant which may be used for phytoremediation. The full‐length BjGT1 cDNA showed homology with the high affinity glutathione transporter HGT1 from Saccharomyces cerevisiae and shares 92% identity with a putative glutathione transporter from A. thaliana (At4g16370). When expressed in the S. cerevisiae hgt1Δ strain, BjGT1 complemented the mutant on medium with glutathione as the only sulphur source and mediated the uptake of [³H]GSH. Immunoblot analysis with a peptide‐specific antiserum directed against a C‐terminal sequence revealed high BjGT1 expression in leaf tissue and relatively low expression in stem tissue, whereas BjGT1 protein was not detectable in root tissue. The amounts of BjGT1 mRNA and protein were analysed during a 6 d exposure of B. juncea to 25 µm Cd(NO₃)₂. BjGT1 mRNA was strongly induced by cadmium in stems and leaves. Unexpectedly, the amount of BjGT1 protein in leaves showed a pronounced decrease with a minimum after 96 h of Cd exposure, followed by partial recovery. The strong regulation of BjGT1 by cadmium suggests a role of this glutathione transporter during heavy metal exposure.     

Context-dependent reproductive site choice in a Neotropical frog

In organisms whose offspring develop in discrete habitat patchessuch as pools, studies have frequently shown that adults avoidsites based on a single risk factor facing offspring. However,natural reproductive sites often vary in multiple risk factorsin both space and time. In this study, I used choice tests amongfield mesocosms to determine whether adults of a Neotropicalanuran, Edalorhina perezi, select the safest pools for offspringbased on two biotic risks of different magnitude: insect predatorsand conspecific competitors. I also investigated whether adultsite-choice was context dependent (i.e., whether it varied bysex or by season or whether it was based on local pool quality).I found that both sexes avoided pools containing predatory insects,but only females significantly avoided those containing conspecifictadpoles. When offered two risky options, both sexes favoredpools with competitors over those with predators. Site-choicebehavior also varied depending on the temporal and spatial context.Female sensitivity to insect predators decreased late in theseason. In addition, both sexes exhibited dampened reproductiveactivity when only risky sites were available locally. Thisstudy emphasizes that social and environmental factors simultaneouslyimpact reproductive site choice. Whether a site is acceptedultimately depends not only on the assessment of mortality risksto offspring but also on the sex and spatiotemporal contextof the decision maker.     

尿苷对线粒体功能的影响

尿苷是生物体内必需的营养物之一,需将尿苷浓度维持在一定浓度水平才能维持胞内正常的生长代谢。近年来,有研究发现尿苷可通过多种机制缓解生物体炎症反应,并能参与胞内糖酵解等代谢途径,且可调节胞内糖基化、乙酰化等蛋白修饰作用。此外,其还能通过减轻胞内氧化应激、促进高能化合物合成等方式保护细胞免受缺氧性损伤。研究表明,这些保护作用与尿苷对线粒体功能的调节作用息息相关。因此,本文主要综述了尿苷及其代谢反应(物)对线粒体功能的研究进展。     

Modifying the endogenous electron fluxes of Rhodobacter sphaeroides 2.4.1 for improved electricity generation

The purple bacteria Rhodobacter sphaeroides serve as a promising biocatalyst in the photo-microbial fuel cell system (photo-MFC). This gram-negative species performs highly efficient anoxygenic photosynthesis that ensures an anaerobic environment in the anode compartment. Previous studies incorporating R. sphaeroides into photo-MFC were conducted using platinum as the anode electrode. In this study, we detected a steady current generation of R. sphaeroides in a bioelectrochemical system where glassy carbon was the working electrode and a typical growth medium was the electrolyte. The bioelectricity generation synchronized with the supplementation of reduced carbon source and showed immediate response to illumination, which strongly indicated the correlation between the observed current and the cytoplasmic quinone activity. Modifications of the endogenous electron flows mediated by quinone pool are shown to have significantly enhanced the bioelectricity generation. We anticipate that the findings in this study would advance future optimization of R. sphaeroides as an anode strain, as well as facilitate the study of bioenergetics in photosynthetic bacteria.     

COSTS AND LIMITS OF PHENOTYPIC PLASTICITY IN ISLAND POPULATIONS OF THE COMMON FROG RANA TEMPORARIA UNDER DIVERGENT SELECTION PRESSURES

Costs and limits are assumed to be the major constraints on the evolution of phenotypic plasticity. However, despite their expected importance, they have been surprisingly hard to find in natural populations. It has therefore been argued that natural selection might have removed high-cost genotypes in all populations. However, if costs of plasticity are linked to the degree of plasticity expressed, then high costs of plasticity would only be present in populations where increased plasticity is under selection. We tested this hypothesis by investigating costs and limits of adaptive phenotypic plasticity in development time in a common garden study of island populations of the common frog Rana temporaria , which have varying levels of development time and phenotypic plasticity. Costs of plasticity were only found in populations with high-plastic genotypes, whereas the populations with the most canalized genotypes instead had a cost of canalization. Moreover, individuals displaying the most extreme phenotypes also were the most plastic ones, which mean we found no limits of plasticity. This suggests that costs of plasticity increase with increased level of plasticity in the populations, and therefore costs of plasticity might be more commonly found in high-plastic populations.     

Assessing and Addressing the Risk of Venous Thromboembolism Across the Spectrum of Gender Affirming Care: A Review

ObjectiveAccumulating evidence demonstrates that gender affirming hormone therapy (GAHT) improves mental health outcomes in transgender persons. Data specific to the risks associated with GAHT for transgender persons continue to emerge, allowing for improvements in understanding, predicting, and mitigating adverse outcomes while informing discussion about desired effects. Of particular concern is the risk of venous thromboembolism (VTE) in the context of both longitudinal GAHT and the perioperative setting. Combining what is known about the risk of VTE in cisgender individuals on hormone therapy (HT) with the evidence for transgender persons receiving HT allows for an informed approach to assess underlying risk and improve care in the transgender community.ObservationsHormone formulation, dosing, route, and duration of therapy can impact thromboembolic risk, with transdermal estrogen formulations having the lowest risk. There are no existing risk scores for VTE that consider HT as a possible risk factor. Risk assessment for recurrent VTE and bleeding tendencies using current scores may be helpful when assessing individual risk. Gender affirming surgeries present unique perioperative concerns, and certain procedures include a high likelihood that patients will be on exogenous estrogens at the time of surgery, potentially increasing thromboembolic risk.Conclusions and RelevanceWithholding GAHT due to potential adverse events may cause negative impacts for individual patients. Providers should be knowledgeable about the management of HT in transgender individuals of all ages, as well as in the perioperative setting, to avoid periods in which transgender individuals are off GAHT. Treatment decisions for both anticoagulation and HT should be individualized and tailored to patients’ overall goals and desired outcomes, given that the physical and mental health benefits of gender affirming care may outweigh the risk of VTE.