Interaction of a biotic factor (predator presence) and an abiotic factor (low oxygen) as an influence on benthic invertebrate communities

We examined the response of benthic invertebrates to hypoxia and predation risk in bioassay and behavioral experiments. In the bioassay, four invertebrate species differed widely in their tolerance of hypoxia. The mayfly, Callibaetis montanus, and the beetle larva, Hydaticus modestus, exhibited a low tolerance of hypoxia, the amphipod, Gammarus lacustris, was intermediate in its response and the caddisfly, Hesperophylax occidentalis, showed high tolerance of hypoxia. In the behavioral experiments, we observed the response of these benthic invertebrates, which differ in locomotor abilities, to vertical oxygen and temperature gradients similar to those in an ice-covered pond. With adequate oxygen, invertebrates typically remained on the bottom substrate. As benthic oxygen declined in the absence of fish, all taxa moved above the benthic refuge to areas with higher oxygen concentrations. In the presence of fish mayflies increased activity whereas all other taxa decreased activity in response to hypoxia. Mayflies and amphipods remained in the benthic refuge longer and endured lower oxygen concentrations whereas the vertical distribution of caddisflies and beetle larvae was not influenced by the presence of fish. As benthic oxygen declined in the presence of fish, all but the beetle larva reduced activity over all oxygen concentrations compared to when fish were absent. As benthic oxygen continued to decline, mayflies and amphipods moved above the benthic refuge and were preyed upon by fish. Thus, highly mobile taxa unable to tolerate hypoxia (mayflies and amphipods) responded behaviorally to declining oxygen concentrations by migrating upward in the water column. Taxa that were less mobile (beetle larvae) or hypoxia-tolerant (caddisflies) showed less of a response. Taxa most vulnerable to fish predation (mayflies and amphipods) showed a stronger behavioral response to predator presence than those less vulnerable (caddisflies and beetle larvae). Because invertebrates differ in their ability to withstand hypoxia, episodes of winter hypoxia could have long-lasting effects on benthic invertebrate communities either by direct mortality or selective predation on less tolerant taxa.     

Trade-offs in the response of mayflies to low oxygen and fish predation

Summary We examined how mayfly larvae (Ephemeroptera,Callibaetis montanus) balance the conflicting demands of avoiding both benthic hypoxia and fish predators. Using vertical oxygen and temperature gradients typical of ice-covered lakes, we observed the behavior of mayflies in the presence and absence of fish. In the absence of fish and with adequate oxygen, mayflies spent most of the time on the bottom substrate. As benthic oxygen concentration declined, mayflies increased their activity and moved up in the water column. In the presence of fish and with adequate oxygen, mayflies spent even more time associated with the bottom substrate and reduced their activity levels. As benthic oxygen concentrations declined, mayflies increased their activity and moved up in the water column, but to a lesser extent than when fish were absent. Because of this depression in activity and reluctance to leave the bottom substrate, mayflies endured lower oxygen concentrations in the face of predation threat relative to when fish were absent. Despite this trade-off, benthic hypoxia resulted in increased mortality due to fish predation. Because benthic invertebrates vary in their ability to tolerate hypoxia and in their vulnerability to fish predators, periods of benthic hypoxia could lead to selective predation on some taxa and be an important force structuring benthic invertebrate assemblages.     

A conserved dileucine motif mediates clathrin and AP-2-dependent endocytosis of the HIV-1 envelope protein

During the assembly of enveloped viruses viral and cellular components essential for infectious particles must colocalize at specific membrane locations. For the human and simian immunodeficiency viruses (HIV and SIV), sorting of the viral envelope proteins (Env) to assembly sites is directed by trafficking signals located in the cytoplasmic domain of the transmembrane protein gp41 (TM). A membrane proximal conserved GYxx? motif mediates endocytosis through interaction with the clathrin adaptor AP-2. However, experiments with SIV(mac239) Env indicate the presence of additional signals. Here we show that a conserved C-terminal dileucine in HIV(HxB2) also mediates endocytosis. Biochemical and morphological assays demonstrate that the C-terminal dileucine motif mediates internalization as efficiently as the GYxx? motif and that both must be removed to prevent Env internalization. RNAi experiments show that depletion of the clathrin adaptor AP-2 leads to increased plasma membrane expression of HIV Env and that this adaptor is required for efficient internalization mediated by both signals. The redundancy of conserved endocytosis signals and the role of the SIV(mac239) Env GYxx? motif in SIV pathogenesis, suggest that these motifs have functions in addition to endocytosis, possibly related to Env delivery to the site of viral assembly and/or incorporation into budding virions.     

Activation of the macroautophagy pathway by Yersinia enterocolitica promotes intracellular multiplication and egress of yersiniae from epithelial cells

The virulence strategy of pathogenic Yersinia spp. involves cell‐invasive as well as phagocytosis‐preventing tactics to enable efficient colonisation of the host organism. Enteropathogenic yersiniae display an invasive phenotype in early infection stages, which facilitates penetration of the intestinal mucosa. Here we show that invasion of epithelial cells by Yersinia enterocolitica is followed by intracellular survival and multiplication of a subset of ingested bacteria. The replicating bacteria were enclosed in vacuoles with autophagy‐related characteristics, showing phagophore formation, xenophagy, and recruitment of cytoplasmic autophagosomes to the bacteria‐containing compartments. The subsequent fusion of these vacuoles with lysosomes and concomitant vesicle acidification were actively blocked by Yersinia. This resulted in increased intracellular proliferation and detectable egress of yersiniae from infected cells. Notably, deficiency of the core autophagy machinery component FIP200 impaired the development of autophagic features at Yersinia‐containing vacuoles as well as intracellular replication and release of bacteria to the extracellular environment. These results suggest that Y. enterocolitica may take advantage of the macroautophagy pathway in epithelial cells to create an autophagosomal niche that supports intracellular bacterial survival, replication, and, eventually, spread of the bacteria from infected cells.     

Prediction of Long-Term Mortality by Preoperative Health-Related Quality-of-Life in Elderly Onco-Surgical Patients

Objective

Aim of this study was to evaluate the association between preoperative health-related quality of life (HRQoL) and mortality in a cohort of elderly patients (>65 years) with gastrointestinal, gynecological and genitourinary carcinomas.

Design

Prospective cohort pilot study.

Setting

Tertiary university hospital in Germany.

Patients

Between June 2008 and July 2010 and after ethical committee approval and written informed consent, 126 patients scheduled for onco-surgery were included. Prior to surgery as well as 3 and 12 months postoperatively all participants completed the EORTC-QLQ-C30 questionnaire (measuring self-reported health-related quality of life). Additionally, demographic and clinical data including the Mini Mental State Examination (MMSE) were collected. Surgery and anesthesia were conducted according to the standard operating procedures. Primary endpoint was the cumulative mortality rate over 12 months after one year. Changes in Quality of life were considered as secondary outcome.

Results

Mortality after one year was 28%. In univariable and multivariable logistic regression analysis baseline HRQoL self-reported cognitive function (OR per point: 0.98; CI 95% 0.96–0.99; p = 0.024) and higher symptom burden for appetite loss (per point: OR 1.02; CI 95% 1.00–1.03; p = 0.014) were predictive for long-term mortality. Additionally the MMSE as an objective measure of cognitive impairment (per point: OR 0.69; CI 95% 0.51–0.96; p = 0.026) as well as severity of surgery (OR 0.31; CI 95% 0.11–0.93; p = 0.036) were predictive for long-term mortality. Global health status 12 months after surgery was comparable to the baseline levels in survivors despite moderate impairments in other domains.

Conclusion

This study showed that objective and self-reported cognitive functioning together with appetite loss were prognostic for mortality in elderly cancer patients. In addition, impaired cognitive dysfunction and severity of surgery were predictive for one-year mortality whereas in this selected population scheduled for surgery age, gender, cancer site and metastases were not.     

Estimating Deer Populations Using Camera Traps and Natural Marks

Despite the ubiquity of camera traps in wildlife monitoring projects, the data gathered are rarely used to estimate wildlife population demographics, a critical step in detecting declines, managing populations, and understanding ecosystem health. In contrast to abundant white-tailed deer (Odocoileus virginianus) in the eastern United States, black-tailed deer (Odocoileus hemionus columbianus) in the western United States have declined over the past several decades. We tested whether passively operating camera traps can be used to quantify population characteristics for black-tailed deer. We used images of naturally occurring physical characteristics of deer to develop movement and activity data and inform a Bayesian spatial mark-resight model that estimates deer abundance, density, sex ratio, ratio of fawns to adult females, and home range size. We developed the model to account for the effect of attractants (bait) on encounter rate. We placed 13 cameras on all known water sources of a private ranch in California and provided bait once a month in front of each camera. Over 9,000 visits occurred between 24 May 2012 and 21 January 2013, and we identified 50 individual deer from ear notches or antler characteristics. We estimated density at 7.7 deer/km² in summer and 8.6 deer/km² in fall. In the summer, home ranges were 2.3 km² for females and fawns and 16.8 km² for males. Home ranges constricted slightly in fall. We estimated a sex ratio of 12.5 males/100 females, and a ratio of 47.0 fawns/100 adult females. Bait increased baseline encounter rates (visits/week) by 3.7 times in summer and 4.95 times in fall. We found slightly higher densities of deer in our study area compared to other recent studies in more mountainous areas of California, and lower male:female sex ratios. This approach shows that commonly deployed camera traps can be used to quantify population characteristics, monitor populations, and inform harvest or habitat management decisions. © 2019 The Wildlife Society.     

Acid-shifted isoelectric point profiles of the proteins in a hypersaline microbial mat: an adaptation to life at high salt concentrations?

In a metagenomic analysis of a stratified hypersaline (9?% salt) microbial mat in Guerrero Negro, Mexico, Kunin et al. (Mol Systems Biol 4:198, 2008) detected a significantly acid-shifted proteome, and concluded that adaptation by enriching proteins with acidic amino acids is more widespread than previously assumed. We here reevaluate these data and conclusions by comparing the isoelectric point profiles of the Guerrero Negro microbial mats (average isoelectric point 6.8) with those of the proteins encoded by the genomes of prokaryotes adapted to different salt concentrations ranges and belonging to different phylogenetic and physiological groups. Average isoelectric points below 6.8 were found not only in the proteomes of the moderately halophilic aerobic bacteria Halomonas elongata and Chromohalobacter salexigens, but even in common types of marine bacteria of the genera Alteromonas and Aliivibrio. We did not find clear evidence that the isoelectric point profile of the Guerrero Negro microbial mat can be considered to be the result of species-independent molecular convergence of the members of the microbial community determined by the salinity of the overlaying brine.