Intermediate Age (intermediate + age)

Distribution by Scientific Domains


Selected Abstracts


Host age and fitness-related traits in a koinobiont aphid parasitoid

ECOLOGICAL ENTOMOLOGY, Issue 4 2005
H. Colinet
Abstract., 1.,Trade-offs play a key role in species evolution and should be found in host,parasitoid interactions where the host quality may differ between host age categories. 2.,The braconid wasp, Aphidius ervi, is a solitary endoparasitoid that allows its aphid hosts to continue to feed and grow after parasitisation. The hypotheses that host age influences their quality and that female parasitoids exploit their hosts based on that quality were tested under laboratory conditions using no-choice tests. 3.,Aphidius ervi females accepted the aphid Myzus persicae for oviposition and their progeny developed successfully in all host ages. The fitness-related traits of parasitoids did not increase linearly with the host age in which they developed. Host quality was found to be optimal at intermediate host ages and the females preferred to parasitise these hosts. The shortest progeny development time and a more female-biased sex ratio were observed in hosts of intermediate age. 4.,This study suggests the existence of multiple interactive trade-offs occurring during host,parasitoid interactions according to host age related quality. [source]


Soil carbon fluxes and stocks in a Great Lakes forest chronosequence

GLOBAL CHANGE BIOLOGY, Issue 1 2009
JIANWU TANG
Abstract We measured soil respiration and soil carbon stocks, as well as micrometeorological variables in a chronosequence of deciduous forests in Wisconsin and Michigan. The chronosequence consisted of (1) four recently disturbed stands, including a clearcut and repeatedly burned stand (burn), a blowdown and partial salvage stand (blowdown), a clearcut with sparse residual overstory (residual), and a regenerated stand from a complete clearcut (regenerated); (2) four young aspen (Populus tremuloides) stands in average age of 10 years; (3) four intermediate aspen stands in average age of 26 years; (4) four mature northern hardwood stands in average age of 73 years; and (5) an old-growth stand approximately 350-years old. We fitted site-based models and used continuous measurements of soil temperature to estimate cumulative soil respiration for the growing season of 2005 (days 133,295). Cumulative soil respiration in the growing season was estimated to be 513, 680, 747, 747, 794, 802, 690, and 571 g C m,2 in the burn, blowdown, residual, regenerated, young, intermediate, mature, and old-growth stands, respectively. The measured apparent temperature sensitivity of soil respiration was the highest in the regenerated stand, and declined from the young stands to the old-growth. Both, cumulative soil respiration and basal soil respiration at 10 °C, increased during stand establishment, peaked at intermediate age, and then decreased with age. Total soil carbon at 0,60 cm initially decreased after harvest, and increased after stands established. The old-growth stand accumulated carbon in deep layers of soils, but not in the surface soils. Our study suggests a complexity of long-term soil carbon dynamics, both in vertical depth and temporal scale. [source]


Formation and evolution of dwarf elliptical galaxies , II.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2009
Spatially resolved star formation histories
ABSTRACT We present optical Very Large Telescope spectroscopy of 16 dwarf elliptical galaxies (dEs) comparable in mass to NGC 205, and belonging to the Fornax cluster and to nearby groups of galaxies. Using full-spectrum fitting, we derive radial profiles of the SSP-equivalent ages and metallicities. We make a detailed analysis with ulyss and steckmap of the star formation history in the core of the galaxies and in an aperture of one effective radius. We resolved the history into one to four epochs. The statistical significance of these reconstructions was carefully tested; the two programs give remarkably consistent results. The old stellar population of the dEs, which dominates their mass, is likely coeval with that of massive ellipticals or bulges, but the star formation efficiency is lower. Important intermediate age (1,5 Gyr) populations and frequently tails of star formation until recent times are detected. These histories are reminiscent of their lower mass dwarf spheroidal counterparts of the Local Group. Most galaxies (10/16) show significant metallicity gradients, with metallicity declining by 0.5 dex over one half-light radius on average. These gradients are already present in the old population. The flattened (or discy), rotating objects (6/16) have flat metallicity profiles. This may be consistent with a distinct origin for these galaxies or it may be due to their geometry. The central single stellar population equivalent age varies between 1 and 6 Gyr, with the age slowly increasing with radius in the vast majority of objects. The group and cluster galaxies have similar radial gradients and star formation histories. The strong and old metallicity gradients place important constraints on the possible formation scenarios of dEs. Numerical simulations of the formation of spherical low-mass galaxies reproduce these gradients, but they require a longer time for them to build up. A gentle depletion of the gas, by ram pressure stripping or starvation, could drive the gas-rich, star-forming progenitors to the present dEs. [source]


Root canal morphology of mandibular permanent molars at different ages

INTERNATIONAL ENDODONTIC JOURNAL, Issue 10 2008
H. R. D. Peiris
Abstract Aim, To investigate differences in the root canal morphology of permanent mandibular molar teeth at various ages. Methodology, Four hundred and eighty permanent mandibular first and second molars were examined. First and second molars were divided into six and five groups, respectively, according to the age of the patient at the time of extraction. Root canal morphology was studied using a clearing technique. The canal morphology of the mesial root was classified into three stages depending on its developmental pattern. When the root canal system was completely differentiated, the canal classification and the number of lateral canals and inter-canal communications were recorded. Vertucci's classification was taken as the main reference. Canal morphology was compared amongst age groups. Results, In both first and second molars, developmental stages of canal morphology amongst age groups were significantly different (P < 0.0001). The prevalence of inter-canal communications was highly significantly different in the first (P < 0.0001) and less significant in the second molar (P < 0.05). After completion of the canal differentiation, the mesial roots of first molars had type IV and II canal forms. The majority of the mesial roots of second molars had type I and III canals. C-shaped canals were found in 3% of second molars. Conclusions, Mesial roots of first and second molars mostly had one large canal until 11 and 15 years of age, respectively. In both molars, the canal system was completely defined at 30,40 years. The prevalence of inter-canal communications was low at young and old ages but high at intermediate ages. [source]


Fitness, developmental instability, and the ontogeny of fluctuating asymmetry in Daphnia magna

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2006
LEIF CHRISTIAN STIGE
Fluctuating asymmetry (FA) is the most commonly used measure of developmental instability. The relation between FA and individual fitness remains controversial, partly due to limited knowledge on the mechanisms behind variation in FA. To address this, we investigated the associations between FA, growth and reproduction as well as the ontogeny of FA in a clonal population of Daphnia magna. FA was not correlated with growth and reproduction, either at the between- or the within-individual level, in a high (N = 48 individuals) or in a low (N = 52 individuals) food-quantity regime. There were therefore no indications of functional effects of FA or of phenotypic trade-offs between developmental stability, growth and reproduction. Individual asymmetries varied randomly in sign and magnitude between subsequent molts (N = 19 individuals, 9,11 instars), but the levels of FA were generally lowest at intermediate ages. No feedback between right and left sides was detected. This suggests that FA only reflects the most recent growth history, that developmental instability may increase in old age, and that FA depends on processes operating on each side of the body independently. The results also suggest that FA differences within and among individual Daphnia are largely random, with limited biological significance. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88, 179,192. [source]