Widespread dieback in a foundation species on a sub-Antarctic World Heritage Island: Fine-scale patterns and likely drivers

Under anthropogenic climate change, emerging diseases and pathogens are increasingly prevalent in high latitude and altitude regions that were previously protected by cold winter temperatures. Ongoing island-wide dieback of a foundation species, the cushion plant Azorella macquariensis, on World Heritage listed Macquarie Island provides the first sub-Antarctic example. To better understand the island-wide progression of cushion dieback and its drivers, we established and quantified plant condition classes and measured microclimate across 62 sites. We then tested whether the drivers of cushion dieback were associated with (i) water stress: represented by vapour pressure deficit, wind exposure and gravel content, (ii) pathogen virulence: using freezing days and extreme humidity as empirically supported surrogates, or (iii) both. There was a strong north-south progression in cushion condition, with dieback most active in the centre of the island and advanced in the north. Dieback was most extensive at sites with fewer freezing days and high humidity. Natural southern refugia were explained by the significantly colder temperatures, associated with a north-south temperature gradient. It is expected that under current climate change trajectories, where Macquarie is likely to continue to become warmer and wetter, cushion dieback will remain pervasive, expanding most slowly in the south and potentially outpacing recovery. We emphasise the need for increased awareness to prevent the establishment of pathogens into and across the landscapes of newly susceptible high latitude and altitude regions. Areas of high conservation significance need to be prioritised for management, to prevent further landscape-scale change under current climate trajectories.     

Efficient infection of cells in culture by type O foot-and-mouth disease virus requires binding to cell surface heparan sulfate.

Foot-and-mouth disease virus (FMDV) enters cells by attaching to cellular receptor molecules of the integrin family, one of which has been identified as the RGD-binding integrin alpha(v)beta3. Here we report that, in addition to an integrin binding site, type O strains of FMDV share with natural ligands of alpha(v)beta3 (i.e., vitronectin and fibronectin) a specific affinity for heparin and that binding to the cellular form of this sulfated glycan, heparan sulfate, is required for efficient infection of cells in culture. Binding of the virus to paraformaldehyde-fixed cells was powerfully inhibited by agents such as heparin, that compete with heparan sulfate or by agents that compete for heparan sulfate (platelet factor 4) or that inactivate it (heparinase). Neither chondroitin sulfate, a structurally related component of the extracellular matrix, nor dextran sulfate appreciably inhibited binding. The functional importance of heparan sulfate binding was demonstrated by the facts that (i) infection of live cells by FMDV could also be blocked specifically by heparin, albeit at a much higher concentration of inhibitor; (ii) pretreatment of cells with heparinase reduced the number of plaques formed compared with that for untreated cells; and (iii) mutant cell lines deficient in heparan sulfate expression were unable to support plaque formation by FMDV, even though they remained equally susceptible to another picornavirus, bovine enterovirus. The results show that entry of type O FMDV into cells is a complex process and suggest that the initial contact with the cell surface is made through heparan sulfate.     

Spatial variation in the ongoing and widespread decline of a keystone plant species

Extensive dieback in dominant plant species in response to climate change is increasingly common. Climatic conditions and related variables, such as evapotranspiration, vary in response to topographical complexity. This complexity plays an important role in the provision of climate refugia. In 2008/2009, an island‐wide dieback event of the keystone cushion plant Azorella macquariensis Orchard (Apiaceae) occurred on sub‐Antarctic Macquarie Island. This signalled the start of a potential regime shift, suggested to be driven by increasing vapour pressure deficit. Eight years later, we quantified cover and dieback across the range of putative microclimates to which the species is exposed, with the aim of explaining dieback patterns. We test for the influence of evapotranspiration using a suite of topographic proxies and other variables as proposed drivers of change. We found higher cover and lower dieback towards the south of the island. The high spatial variation in A. macquariensis populations was best explained by latitude, likely a proxy for macroscale climate gradients and geology. Dieback was best explained by A. macquariensis cover and latitude, increasing with cover and towards the north of the island. The effect sizes of terrain variables that influence evapotranspiration rates were small. Island‐wide dieback remains conspicuous. Comparison between a subset of sites and historical data revealed a reduction of cover in the north and central regions of the island, and a shift south in the most active areas of dieback. Dieback remained comparatively low in the south. The presence of seedlings was independent of dieback. This study provides an empirical baseline for spatial variation in the cover and condition of A. macquariensis, both key variables for monitoring condition and ‘cover‐debt’ in this critically endangered endemic plant species. These findings have broader implications for understanding the responses of fellfield ecosystems and other Azorella species across the sub‐Antarctic under future climates.     

Comprehensive genetic evaluation of common E-cadherin sequence variants and prostate cancer risk: strong confirmation of functional promoter SNP

The E-cadherin gene (CDH1) has been proposed as a prostate cancer (PC) susceptibility gene in several studies. Aberrant protein expression has been related to prognosis and progression in PC. In addition, a functional promoter SNP (rs16260) has been found to associate with PC risk. We performed a comprehensive genetic analysis of CDH1 by using the method of haplotype tagged SNPs in a large Swedish population-based case-control study consisting of 801 controls and 1,636 cases. In addition, Swedish PC families comprising a total of 157 cases sampled for DNA were analyzed for selected SNPs. Seven SNPs, including the promoter SNP rs16260, that captured over 96% of CDH1 haplotype variation were selected as haplotype tagging SNPs and analyzed for associated PC risk. We observed significant confirmation of rs16260 (P=0.003) for cases with a positive family history of PC (FH+) both in an independent case-control population and in PC families. In addition, a common haplotype (HapB, 25%) including the variant allele of rs16260 was associated (P=0.004) with PC risk among FH+ cases. The promoter SNP rs16260 as well as HapB were significantly transmitted to affected offspring in PC families. We report strong confirmation of the association between PC risk in FH+ cases and a functional CDH1 promoter SNP in an independent population. In conjunction with the biological importance of CDH1 our findings encourage further evaluation of genetic variation in CDH1 in relation to PC etiology. Due to the difficulties in replication of genetic association studies, this finding is unusual and novel.     

TNBS-induced inflammation modulates the function of one class of low-threshold rectal mechanoreceptors in the guinea pig

The effects of trinitrobenzene sulfonic acid (TNBS)-induced inflammation on specialized, low-threshold, slowly adapting rectal mechanoreceptors were investigated in the guinea pig. Under isoflurane anesthesia, 300 microl saline or TNBS (15 mg/ml) in 30% ethanol was instilled 7 cm from the anal sphincter. Six or 30 days later, single unit extracellular recordings were made from rectal nerve trunks in flat-sheet in vitro preparations attached to a mechanical tissue stretcher. TNBS treatment caused macroscopic ulceration of the rectal mucosa at 6 days, which fully resolved by 30 days. Muscle contractility was unaffected by TNBS treatment. At 6 days posttreatment, responses of low-threshold rectal mechanoreceptors to circumferential stretch were increased, and the proportion of afferents responding with von Frey hair thresholds 相似文献