Many examples of biased sex ratios are known in natural populations of plants. Proximal causes of these biases are gender diphasy (sex changing), differential mortality between male and female ...genets, differential rates of clonal growth (numbers of ramets per genet), and differential flowering (differences in flowering frequency or age to maturity). In the western North American shrub Oemleria cerasiformis we determined sex ratios for 60 natural populations and found an excess of males in 56 populations. The male bias was greatest in populations with little recent recruitment. Sampling of young and old plants indicated that males flowered at an earlier age than females, which led to a transient flowering bias in very young plants, and that the genet sex ratio was 1:1 in young mature plants but male biased in old plants, as a result of differential mortality. Examination of dead genets confirmed that mature females have higher mortality rates. Females also have greater reproductive effort and slower growth rates than males. The major cause of biased sex ratios in O. cerasiformis is greater mortality of female plants during their reproductive years, which probably arises directly or indirectly from their greater allocation to reproduction.
Abstract In vitro generation of cardiomyocytes (CMs) from human cells opens the possibility to develop patient-specific therapies to various cardiomyopathies. By establishing the in vitro ...reprograming methods that produce human CMs, we learn about what is involved in the development of specific CM subtypes. In this review, we summarize the latest achievements in CM generation technologies, emphasizing the differentiation methods of specific CM subtypes. We also relate the biological properties and functions of the in vitro -generated CMs to those of their in vivo counterparts. Furthermore, we describe the main problem of current CM derivation methods – maturation of CMs. We subsequently discuss biochemical and physical stimuli that are used to overcome the maturation problems of in vitro -derived CMs. As a result, a more holistic approach with controllable environment and timing of specific stimuli for creation of more mature engineered heart tissues is described as well. Finally, we propose a novel approach in which enhancing energy transfer mechanisms in the immature CMs might help to overcome the current hurdle of incomplete in vitro differentiation.
We examined the size, age, and spatial structure of trees in an old Engelmann spruce (Picea engelmannii)-subalpine fir (Abies lasiocarpa) forest based on four stem-mapped, 0.25 ha plots. ...Dendrochronological techniques were used on basal discs of 1,190 trees to reconstruct age and growth pattern, including dates of rapid growth increases. There were no obvious age cohorts or other evidence of past major disturbance. The abundance of both subalpine fir and spruce decreased rapidly with age, especially beyond the ages of 150 years. Very old trees were present, but rare. The best evidence from tree-ring width patterns for past disturbance was a period of release 100 years ago. However, few of the released trees grew into the canopy, which suggests a disturbance of low intensity. Patch dynamics and gap processes were not pronounced in the stand. Clumping was generally weak and only present at small spatial scales (<5 m) for live trees, and largely non-existent for dead trees; mortality was spatially random in this forest. Although spruce were sparse (5.1% of trees) in the forest relative to fir, which is consistent with predictions that fir will ultimately replace spruce in the absence of disturbance, coexistence seems more likely judging from the age structure and numbers of dead trees. In contrast to almost all spruce-fir forests studied previously, the stand we examined showed no record of major disturbances. Thus this stand falls at the limit of the range of dynamics -- from disturbance-structured to near steady-state -- encompassed in current thinking about forest ecosystems.
We used dendrochronological analysis of over 2000 trees in four 50 x 50 m plots to reconstruct the history and dynamics of a 330-year-old, fire-initiated spruce-fir forest. All lodgepole pine (Pinus ...contorta Dougl. ex Loud.), half of the canopy Engelmann spruce (Picea engelmannii Parry ex Engelm.), but less than 10% of the canopy subalpine fir (Abies lasiocarpa (Hook.) Nutt.) dated from the first 50 years of stand development. Tree-ring patterns of individual surviving trees showed no evidence of disturbance during the first 200 years after stand initiation; subsequently, episodes of disturbance are indicated by periods of release in understory fir. Although many fir owe their canopy position to release after disturbance, few canopy fir in the current stand established in response to either the stand-initiating event or subsequent partial disturbances. A seedling bank of long-lived fir appears critical to the dynamics of this forest. In contrast, establishment of almost all canopy spruce can be related to disturbance. This stand, although fire initiated, was structured primarily by a combination of partial disturbances and autogenic processes. We suspect that most old, fire-initiated stands in many forest regions are similarly structured and emphasize that the contribution of partial disturbances and autogenic processes should be fully assessed when examining their dynamics or managing such forests.
Celotno besedilo
Dostopno za:
BF, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The broad utility of protein bioconjugates has created a need for new and diverse strategies for site-selective protein modification. In particular, chemical reactions that target alternative amino ...acid side chains or unnatural functional groups are emerging as a valuable complement to more commonly used lysine- and cysteine-based strategies. Considering their widespread use in organic synthesis, reactions catalyzed by transition metals could provide a particularly powerful set of transformations for the continued expansion of the bioconjugation toolkit. Recent efforts to apply transition metal catalysis to protein modification have resulted in new methods for protein cross-linking, tryptophan modification, tyrosine modification, reductive amination of protein amines, and unnatural amino acid labeling. These strategies have substantially expanded the synthetic flexibility of protein modification, and thus the range of applications for which bioconjugates can be used in chemical biology and materials science.
Tree mortality is a key driver of forest dynamics and its occurrence is projected to increase in the future due to climate change. Despite recent advances in our understanding of the physiological ...mechanisms leading to death, we still lack robust indicators of mortality risk that could be applied at the individual tree scale. Here, we build on a previous contribution exploring the differences in growth level between trees that died and survived a given mortality event to assess whether changes in temporal autocorrelation, variance, and synchrony in time-series of annual radial growth data can be used as early warning signals of mortality risk. Taking advantage of a unique global ring-width database of 3065 dead trees and 4389 living trees growing together at 198 sites (belonging to 36 gymnosperm and angiosperm species), we analyzed temporal changes in autocorrelation, variance, and synchrony before tree death (diachronic analysis), and also compared these metrics between trees that died and trees that survived a given mortality event (synchronic analysis). Changes in autocorrelation were a poor indicator of mortality risk. However, we found a gradual increase in inter-annual growth variability and a decrease in growth synchrony in the last ∼20 years before mortality of gymnosperms, irrespective of the cause of mortality. These changes could be associated with drought-induced alterations in carbon economy and allocation patterns. In angiosperms, we did not find any consistent changes in any metric. Such lack of any signal might be explained by the relatively high capacity of angiosperms to recover after a stress-induced growth decline. Our analysis provides a robust method for estimating early-warning signals of tree mortality based on annual growth data. In addition to the frequently reported decrease in growth rates, an increase in inter-annual growth variability and a decrease in growth synchrony may be powerful predictors of gymnosperm mortality risk, but not necessarily so for angiosperms.
The dynamics of an old-growth Engelmann spruce (Picea engelmannii Parry)-subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forest were investigated using stand-history reconstruction. Age and size ...structures, tree location, and radial increment patterns were used to link establishment and growth to disturbances. The spatial distribution of trees was used to infer patterns of establishment and mortality. The forest originated in the 1650s, probably after fire. Initial establishment took almost 80 years, after which fir continued to recruit effectively, but spruce did not. The tree-ring record showed no evidence of widespread disturbance during the first 200 years, but from about 1855 to 1900 a major period of canopy mortality caused by bark beetles released suppressed trees and provided opportunities for establishment and rapid growth of seedlings of both species. Most current canopy trees established or released during this period of disturbance; thus, many canopy trees are fairly young in this old-growth forest and canopy turnover is high. A short period of disturbance (1927-1932) caused by the balsam bark beetle (Dryocoetes confusus Swaine) resulted in release of suppressed trees but did not promote seedling establishment. At the time of study (1994), the stand was undergoing another minor disturbance caused by this insect. Bark beetles appear to be of fundamental importance in controlling the dynamics of spruce-fir forests during the long intervals that often occur between fires in cool, wet climates.
Clonal herbs that attain maximum development in late-seral forest are often assumed to have similar responses to disturbance and to be functionally equivalent. However, little is known about the ...demographic or physiological responses of these plants to disturbance or to the altered conditions of the post-disturbance environment. Following harvest of a mature coniferous forest, we compared abundance, demographic changes, and physiological acclimation of three clonal herbs (Asarum caudatum, Clintonia uniflora, and Pyrola picta) that differ in belowground morphology and leaf longevity. We measured ramet density, leaf area, and demographic variables (survival, clonal growth, flowering, and seedling establishment) before and for two years after harvest, and in adjacent undisturbed forest. Acclimation to increased solar radiation was assessed two years after harvest, by measuring leaf mass per unit area (LMA) and chlorophyll a:b ratios of leaves produced in the current year. Although initial declines in abundance were similar, demographic responses indicate that patterns of recovery varied greatly among species. Two years after logging, ramet survival and clonal growth (production of new ramets) of Clintonia were greater in the harvest area than in the forest. Asarum had lower survival in the harvest area, but greater clonal growth, and Pyrola showed no difference in either survival or growth between environments. Only Asarum produced seedlings, although their survival was low in the harvest area. All species had higher LMA in the harvest area, but only Clintonia (with annual leaves) had a higher chlorophyll a:b ratio, suggesting the greatest potential for acclimation to increased light. Our results demonstrate that forest herbs with greater rhizome plasticity and shorter leaf duration have greater potential to acclimate after disturbance than those with rigid architectures and persistent leaves. Thus, species with comparable successional roles can vary substantially in their demographic and physiological responses to disturbance, with potential consequences for long-term recovery.
An updated measurement of the single top quark production cross section is presented using the full data set collected by the Collider Detector at Fermilab (CDF), corresponding to 9.5fb super(-1) of ...integrated luminosity from proton-antiproton collisions at 1.96 TeV center-of-mass energy. The events selected contain an imbalance in the total transverse momentum, jets identified as containing b quarks, and no identified leptons. The sum of the s- and t-channel single top quark cross sections is measured to be (ProQuest: Formulae and/or non-USASCII text omitted)pb and a lower limit on the magnitude of the top-to-bottom quark coupling, V sub(t)bof 0.63, is obtained at the 95% credibility level. These measurements are combined with previously reported CDF results obtained from events with an imbalance in total transverse momentum, jets identified as originating from b quarks, and one identified lepton. The combined cross section is measured to be (ProQuest: Formulae and/or non-USASCII text omitted)pb and a lower limit on V sub(t)bof 0.84 is obtained at the 95% credibility level.
We examined the potential of natural regeneration for stocking 1-ha patch cuts in high-elevation Engelmann spruce (Picea engelmannii Parry) - subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forests. ...Using the Sicamous Creek Silvicultural Systems site, which was harvested during winter 1994-1995, we established 1-m2 plots in patch cuts, forest edge, and untreated control forest. We marked and recorded microsite characteristics for all advanced regeneration and new recruits for up to 5 years; over 12 000 individuals were included. Advanced regeneration was abundant and was about one-quarter spruce. Spruce and fir germinants occurred in all years, but numbers varied greatly, with a very large cohort in 1998. Both advanced regeneration and new recruits were concentrated on decaying logs. Mortality of advanced regeneration was high in the patch cuts following harvest, but subsequent survival was good, approaching rates in the untreated forest within 4 years. Survival rates were higher for spruce than fir, but differed little among surface types and microtopographic positions. Survival of new recruits was high, approximately 50% the first year and 70% during the second, and was similar between spruce and fir. If the 1998 cohort has similar survival, the patch cuts could be adequately stocked. Use of natural regeneration, in combination with infill planting, is a viable option for stocking small openings in wet high-elevation forests in southern British Columbia.
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