Age–size–habitat relationships for <Emphasis Type="Italic">Polylepis australis</Emphasis>: dealing with endangered forest ecosystems

Assessing tree ages is important for the understanding of forest recruitment patterns and tree growth. However, little experience exists in the subtropics and accurate aging usually involves potentially damaging techniques such as tree coring or even the use of entire cross sections, which is not recommendable in endangered species or ecosystems. We provide an example of how age may be predicted on the basis of tree size and site conditions, using Polylepis australis of Central Argentina. Our study was conducted in two entire river basins where 96 independent trees were successfully cored for age analysis. Site and tree characteristics were registered and tree age determined through standard dendrochronological techniques. The multiple regression procedure selected tree circumference and proportion of rock under the tree canopy as significant variables explaining 48% of the variation in number of growth rings. Trees surrounded by rock clearly grew slower than those surrounded by a higher proportion of soil and vegetation. A comparison with a one site study shows that the ability to predict P. australis age is clearly reduced when geographical range is extended but the explanatory power of our model is still high enough for certain applications and within the range of other one site studies. We suggest that tree size and site characteristics may be used to predict age in other subtropical mountain forests with a well marked growth season.     

Expression of Tight Junction Proteins and Cadherin 17 in the Small Intestine of Young Goats Offered a Reduced N and/or Ca Diet

Diets fed to ruminants should contain nitrogen (N) as low as possible to reduce feed costs and environmental pollution. Though possessing effective N-recycling mechanisms to maintain the N supply for rumen microbial protein synthesis and hence protein supply for the host, an N reduction caused substantial changes in calcium (Ca) and phosphate homeostasis in young goats including decreased intestinal transepithelial Ca absorption as reported for monogastric species. In contrast to the transcellular component of transepithelial Ca transport, the paracellular route has not been investigated in young goats. Therefore, the aim of the present study was to characterise the effects of dietary N and/or Ca reduction on paracellular transport mechanisms in young goats. Electrophysiological properties of intestinal epithelia were investigated by Ussing chamber experiments. The expression of tight junction (TJ) and adherens junction (AJ) proteins in intestinal epithelia were examined on mRNA level by qPCR and on protein level by western blot analysis. Dietary N reduction led to a segment specific increase in tissue conductances in the proximal jejunum which might be linked to concomitantly decreased expression of cadherin 17 mRNA. Expression of occludin (OCLN) and zonula occludens protein 1 was increased in mid jejunal epithelia of N reduced fed goats on mRNA and partly on protein level. Reduced dietary Ca supply resulted in a segment specific increase in claudin 2 and claudin 12 expression and decreased the expression of OCLN which might have been mediated at least in part by calcitriol. These data show that dietary N as well as Ca reduction affected expression of TJ and AJ proteins in a segment specific manner in young goats and may thus be involved in modulation of paracellular Ca permeability.     

Multiple common garden experiments suggest lack of local adaptation in an invasive ornamental plant

Aims Adaptive evolution along geographic gradients of climatic conditions is suggested to facilitate the spread of invasive plant species, leading to clinal variation among populations in the introduced range. We investigated whether adaptation to climate is also involved in the invasive spread of an ornamental shrub, Buddleja davidii, across western and central Europe.Methods We combined a common garden experiment, replicated in three climatically different central European regions, with reciprocal transplantation to quantify genetic differentiation in growth and reproductive traits of 20 invasive B. davidii populations. Additionally, we compared compensatory regrowth among populations after clipping of stems to simulate mechanical damage.Important findings Our results do not provide evidence for clinal variation among invasive B. davidii populations: populations responded similarly to the different environments, and trait values were not correlated to climatic conditions or geographic coordinates of their home sites. Moreover, we did not detect differences in the compensatory ability of populations. We suppose that the invasive spread of B. davidii has been facilitated by phenotypic plasticity rather than by adaptation to climate and that continent-wide shuffling of cultivars due to horticultural trade may have limited local adaptation so far.     

Post-Fire Population Dynamics of Two Tree Species in High-Altitude Polylepis Forests of Central Ecuador

Fire is considered the main cause for the patchy distribution of high-montane tropical forests growing below the upper limit of tree growth, but there are little quantitative data on the impacts of burning on the respective tree populations. This study compares adult tree survival as well as sapling (0.05–1.3 m) and seedling (<0.05 m) recruitment of Polylepis incana , and the coexisting Gynoxis acostae in burned and unburned forest stands in the Páramo de Guamaní, central Ecuador. In P. incana , adult survival after burning was low, whereas all G. acostae individuals survived through resprouting. Two years after fire, the density of P. incana seedlings and saplings was higher than that of G. acostae , but still not sufficient for forest recovery. A sowing experiment revealed a significantly lower seedling emergence of both species in the burned than in the unburned plots. Seedling emergence was comparable to laboratory studies performed under optimal conditions, suggesting there was no evidence for climate constraining emergence at the given altitude. Interactions between seedling survival and burning for P. incana indicate higher seedling survival after burning, which could not be shown for G. acostae . Our data imply that single fire events strongly decrease adult and seedling population sizes in P. incana and thus may be the main reason for the discontinuous forest distribution below the upper distribution limit of the species. In contrast, the high resprouting potential of G. acostae explains its relatively high percentage in the remaining Ecuadorian P. incana stands.     

The words of the regulatory code are arranged in a variable manner in highly conserved enhancers

The mammillary body, a ventral specialization of the caudal hypothalamus, lies close to the transition between epichordal and prechordal parts of the forebrain (Puelles and Rubenstein, 2003). This report examines its presumed causal connection with either prechordal or notochordal mesodermal induction, as well as the timing of its specification, in the context of early ventral forebrain patterning. It was recently found that the ephrin receptor gene EphA7 is selectively expressed in the mammillary pouch from early stages of development (HH14: García-Calero et al., 2006). We used mammillary EphA7 expression as well as ventral hypothalamic expression of the gene markers Nkx2.1 and Shh to analyze experimental effects on mammillary specification and morphogenesis after axial mesoderm ablation at stages HH4+ to HH6. Progressively delayed ablation of the prechordal plate revealed its sequential implication in molecular specification of the entire ventral forebrain, including the mammillary and tuberal regions of the hypothalamus. We observed differential contact requirements for induction by the prechordal plate of all the forebrain regions expressing Shh and Nkx2.1, including distant subpallial ones. In contrast, ablation of the anterior notochordal tip at these stages did not elicit significant patterning changes, particularly no effects on mammillary EphA7 expression or mammillary pouch development.     

Mercapturic acids of acrylamide and glycidamide as biomarkers of the internal exposure to acrylamide in the general population

Acrylamide (AA), a widely used industrial monomer which is categorised to be carcinogenic, was found to be generated in starch-containing foods during the heating process. This discovery has caused reasonable concern about possible health risks to humans due to dietary acrylamide uptake. In order to gain more information on human metabolism of acrylamide and to contribute to the assessment of the human carcinogenic risk due to AA uptake we measured the mercapturic acid of AA and its epoxide glycidamide (GA) i.e. N-acetyl-S-(2-carbamoylethyl)-L-cysteine (AAMA) and N-(R,S)-acetyl-S-(2-carbamoyl-2-hydroxyethyl)-L-cysteine (GAMA) in human urine. The relation between AAMA and GAMA is important in this context because GA is thought to be the ultimate carcinogenic metabolite of AA.The median levels in smokers (n = 13) were found to be about four times higher than in non-smokers (n = 16) with median levels of 127 μg/l versus 29 μg/l for AAMA and 19 μg/l versus 5 μg/l for GAMA. Therefore cigarette smoke proved to be an important source of acrylamide exposure. The level of AAMA in the occupationally non-exposed collective (n = 29) ranged from 3 to 338 μg/l, the level of GAMA from <LOD to 45 μg/l. The ratio of GAMA:AAMA varied from 0.03 to 0.53, median was 0.16 which is in reasonable agreement with results of different studies on rats. Thus the metabolic conversion of acrylamide to its genotoxic epoxide glycidamide seems to occur to a comparable extent in rats and humans. Consequently, risk estimations by various authorities based on experimental data obtained in rats are supported by our findings. Besides we also measured the haemoglobin adducts of AA and GA in the blood of 26 participants. From these results compared to the mercapturic acids, we deduce a steady state for AA uptake, and we demonstrate a higher reactivity of GA in comparison to AA towards haemoglobin compared to glutathione in humans.