Lack of geographic variation in anonymous nuclear polymorphisms in the American oyster, Crassostrea virginica

Comparing geographic variation of noncoding nuclear DNA polymorphisms, which presumably are neutral to natural selection, with geographic variation of allozymes is potentially a good way to detect the effects of selection on allozyme polymorphisms. A previous study of four anonymous nuclear markers in the American oyster, Crassostrea virginica, found dramatic differences in allele frequency between the Gulf of Mexico and the Atlantic Ocean. In contrast, 14 allozyme polymorphisms were fairly uniform in frequency between the two areas. This led to the conclusion that all of the allozyme polymorphisms were kept uniform in frequency by balancing selection. To test the robustness of this pattern, six additional anonymous nuclear DNA polymorphisms were surveyed in oysters from Panacea, Fla, and Charleston, S.C. on the Gulf and Atlantic coasts, respectively. Unlike the previously studied DNA markers, the six DNA polymorphisms examined here show geographic variation that is not significantly greater than that of allozymes. The reason for the discrepancy between the two sets of DNA polymorphisms is unclear.      

Noninvasive Measurement of Vulnerability to Drought-Induced Embolism by X-Ray Microtomography

Hydraulic failure induced by xylem embolism is one of the primary mechanisms of plant dieback during drought. However, many of the methods used to evaluate the vulnerability of different species to drought-induced embolism are indirect and invasive, increasing the possibility that measurement artifacts may occur. Here, we utilize x-ray computed microtomography (microCT) to directly visualize embolism formation in the xylem of living, intact plants with contrasting wood anatomy (Quercus robur, Populus tremula × Populus alba, and Pinus pinaster). These observations were compared with widely used centrifuge techniques that require destructive sampling. MicroCT imaging provided detailed spatial information regarding the dimensions and functional status of xylem conduits during dehydration. Vulnerability curves based on microCT observations of intact plants closely matched curves based on the centrifuge technique for species with short vessels (P. tremula × P. alba) or tracheids (P. pinaster). For ring porous Q. robur, the centrifuge technique significantly overestimated vulnerability to embolism, indicating that caution should be used when applying this technique to species with long vessels. These findings confirm that microCT can be used to assess the vulnerability to embolism on intact plants by direct visualization.Theory describing the physiological mechanism that allows plants to extract water from the soil and transport it many tens of meters in height has often been the subject of intense debate (Tyree, 2003). Plants have evolved a water-transport system that relies on water sustaining a tensile force; as a result, xylem sap is at negative absolute pressures (Dixon and Joly, 1895; Melcher et al., 1998; Wei et al., 1999). However, this transport mechanism comes with its own set of problems. Most notably, water under tension is prone to cavitation, which results in the formation of gas bubbles (emboli) that block xylem conduits. Embolism reduces the capacity of the xylem tissue to deliver water to the canopy, where it is required to maintain adequate levels of cellular hydration (Tyree and Sperry, 1989). The probability of embolism occurring in the xylem increases during drought, with increasing tension in the xylem sap. During prolonged and severe droughts, xylem embolism can reach lethal levels, causing branch dieback and, ultimately, plant death (Davis et al., 2002; Brodribb and Cochard, 2009; Hoffmann et al., 2011; Choat, 2013; Urli et al., 2013). Water stress-induced embolism is now recognized as one of the principal causes of plant mortality in response to extreme drought events (Anderegg, 2015). In the face of increasingly severe droughts expected with rising global temperatures, hydraulic failure due to embolism has the potential to cause widespread dieback of trees across all major forest biomes (Choat et al., 2012).The majority of techniques used to estimate cavitation resistance are indirect and/or invasive, increasing the possibility of artifacts occurring during measurement (Cochard et al., 2013). Artifacts relating to invasive techniques are particularly relevant in this case, since xylem sap under tension is in a metastable state and may easily vaporize as a result of disturbance. Noninvasive imaging techniques offer the potential to make direct observations of xylem function in intact plants at high resolution and in real time. Noninvasive techniques include magnetic resonance imaging (MRI; Holbrook et al., 2001; Kaufmann et al., 2009; Choat et al., 2010) and, more recently, x-ray computed microtomography (microCT; Brodersen et al., 2010; Charra-Vaskou et al., 2012; McElrone et al., 2012). MicroCT provides superior spatial resolution to MRI, with resolutions below 2 μm attainable for a plant stem of 4 to 5 mm in diameter. This allows for detailed analysis of embolism formation and repair in the xylem, including spatial patterns of embolism spread between conduits (Brodersen et al., 2013; Dalla-Salda et al., 2014).However, noninvasive imaging techniques have seldom been used to validate indirect or invasive techniques used to estimate cavitation resistance. At this stage, only a handful of studies have utilized imaging technology to measure cavitation resistance in trees (Torres-Ruiz et al., 2014; Cochard et al., 2015), and these studies employed a destructive mode of the technique in which small branches were cut off the plant before scanning took place. Thus far, noninvasive imaging on intact plants has only been used to measure cavitation resistance in two species, grapevine (Vitis vinifera; Choat et al., 2010; Brodersen et al., 2013) and Sequoia sempervirens (Choat et al., 2015). Further measurement of cavitation resistance using noninvasive imaging on intact plants across a range of species, therefore, is a high priority.These comparisons are particularly important because of the current debate surrounding the invasive techniques (Cochard et al., 2013). Specifically, evidence from a variety of experiments suggests that centrifuge and air injection techniques underestimate cavitation resistance in species with long xylem vessels (Choat et al., 2010; Cochard et al., 2010; Ennajeh et al., 2011; Martin-StPaul et al., 2014; Torres-Ruiz et al., 2014; Wang et al., 2014). This artifact occurs when samples placed into centrifuge rotors or air injection collars have a large proportion of vessels that are cut open at both ends of the segment. A number of studies have disputed this open-vessel hypothesis and suggested that some versions of the centrifuge and air injection techniques provide reliable estimates of cavitation resistance (Jacobsen and Pratt, 2012; Sperry et al., 2012; Tobin et al., 2013). Because there will always be uncertainties associated with indirect measurements, noninvasive imaging using intact plants provides the best option for resolving these methodological issues.In this study, synchrotron-based microCT was utilized to investigate the formation of drought-induced embolism in the xylem of intact, potted plants. Three species were selected to provide a range of contrasting xylem structures: Quercus robur (ring porous), Populus tremula × Populus alba (diffuse porous), and Pinus pinaster (tracheid bearing). Visualizations of xylem embolism in the stems of these species during a sequence of natural dehydration were used to construct embolism vulnerability curves. We hypothesized that (1) vulnerability curves based on microCT observations would match vulnerability curves based on the centrifuge technique for species with short vessels (P. tremula × P. alba) or tracheid-based xylem (P. pinaster) and (2) the centrifuge technique would overestimate vulnerability to embolism in the long-vesseled species (Q. robur) due to the open-vessel artifact.     

Recruitment dynamics and first year growth of the coral reef surgeonfish Ctenochaetus striatus,with implications for acanthurid growth models

Newly recruited Ctenochaetus striatus were monitored over a 16-month period in American Samoa, 2002–2003. During this period, a mass recruitment of age-0 C. striatus occurred in March 2002 with numbers reaching 22.9 recruits m^?2. This program provided an invaluable opportunity to (1) analyze the dynamics of a mass recruitment episode and to assess its significance with respect to more typical patterns of recruitment and (2) establish the pattern of recruit growth during their first year of life. Age-based analysis indicated that the mass recruitment generated about 90 % of annual recruitment, but recruit mortality was high; thus, most recruitment was provided by continuous settlement throughout the year. The mass event appeared to be a short-lived pulse with recruits residing on the reef an average of 14.1 d compared with 161.1 d for other recruits. Recruits grew rapidly, achieving 90 % of their adult size during their first year, and they formed their first otolith annulus after 1 yr, thereby providing a firm basis for otolith interpretation of fish ages during the early life history phase of this species. The extensive age-based documentation of their first year growth in this study validates the distinctive “square” growth pattern exhibited by acanthurids as described in the literature (i.e., long life span with rapid initial growth that quickly reaches an asymptotic size), and it demonstrates the impact that the presence of age-0 fish has when generating growth parameters for populations exhibiting square growth. We found that the parameters from the re-parameterized von Bertalanffy growth function have preferred characteristics when modeling square growth in fish and that fixing age-at-length zero to pelagic larval duration is a preferable method to constrain growth models when lacking age-0 fish.     

Rituximab treatment in rheumatoid arthritis: how does it work?

Treatment with the chimerical monoclonal antibody rituximab results in CD20-directed B cell depletion. Although this depletion is almost complete in the peripheral blood of nearly all patients with rheumatoid arthritis, a proportion of patients does not exhibit a clinical response. The paper by Nakou and colleagues suggests that a decrease in CD19+CD27+ memory B cells in both peripheral blood and bone marrow precedes the clinical response to rituximab. This finding adds to the emerging evidence that lack of response to rituximab is associated with persistence of B lineage cells in specific body compartments.     

The world’s largest parrotfish has slow growth and a complex reproductive ecology

Coral Reefs - The bumphead parrotfish (Bolbometopon muricatum) is an iconic coral reef species of commercial, subsistence, and cultural value that has faced severe declines across the Indo-Pacific....     

Molecular docking of alkaloid compounds with the matrix metalloproteinase 2

Matrix metalloproteinase protein-2 (MMP-2) is linked to the human oral squamous cell carcinoma. Therefore, it is of interest to design new inhibitors for MMP-2 to combat the disease. Thus, we document the molecular docking features of Aristolochic acid, Cryptopleurine, Epipodophyllotoxin, and Fagaronine with MMP-2 for further consideration.     

Patterns and processes in the evolutionary history of parrotfishes (Family Labridae)

Phylogenetic reconstruction of the evolutionary relationships among 61 of the 70 species of the parrotfish genera Chlorurus and Scarus (Family Labridae) based on mitochondrial and nuclear gene sequences retrieved 15 well‐supported clades with mid Pliocene/Pleistocene diversification. Twenty‐two reciprocally monophyletic sister‐species pairs were identified: 64% were allopatric, and the remainder were sympatric. Age of divergence was similar for allopatric and sympatric species pairs. Sympatric sister pairs displayed greater divergence in morphology, ecology, and sexually dimorphic colour patterns than did allopatric pairs, suggesting that both genetic drift in allopatric species pairs and ecologically adaptive divergence between members of sympatric pairs have played a role in diversification. Basal species typically have small geographical ranges and are restricted to geographically and ecologically peripheral reef habitats. We found little evidence that a single dominant process has driven diversification, nor did we detect a pattern of discrete, sequential stages of diversification in relation to habitat, ecology, and reproductive biology. The evolution of Chlorurus and Scarus has been complex, involving a number of speciation processes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 529–557.