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Growth Zones (growth + zone)
Selected AbstractsTerminal addition, the Cambrian radiation and the Phanerozoic evolution of bilaterian formEVOLUTION AND DEVELOPMENT, Issue 6 2005David K. Jacobs Summary We examine terminal addition, the process of addition of serial elements in a posterior subterminal growth zone during animal development, across modern taxa and fossil material. We argue that terminal addition was the basal condition in Bilateria, and that modification of terminal addition was an important component of the rapid Cambrian evolution of novel bilaterian morphology. We categorize the often-convergent modifications of terminal addition from the presumed ancestral condition. Our focus on terminal addition and its modification highlights trends in the history of animal evolution evident in the fossil record. These trends appear to be the product of departure from the initial terminal addition state, as is evident in evolutionary patterns within-fossil groups such as trilobites, but is also more generally related to shifts in types of morphologic change through the early Phanerozoic. Our argument is contingent on dates of metazoan divergence that are roughly convergent with the first appearance of metazoan fossils in the latest Proterozoic and Cambrian, as well as on an inference of homology of terminal addition across bilaterian Metazoa. [source] Spatial and Temporal Quantitative Analysis of Cell Division and Elongation Rate in Growing Wheat Leaves under Saline ConditionsJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 1 2008Yuncai Hu Abstract Leaf growth in grasses is determined by the cell division and elongation rates, with the duration of cell elongation being one of the processes that is the most sensitive to salinity. Our objective was to investigate the distribution profiles of cell production, cell length and the duration of cell elongation in the growing zone of the wheat leaf during the steady growth phase. Plants were grown in loamy soil with or without 120 mmol/L NaCl in a growth chamber, and harvested at day 3 after leaf 4 emerged. Results show that the elongation rate of leaf 4 was reduced by 120 mmol/L NaCl during the steady growth phase. The distribution profile of the lengths of abaxial epidermal cells of leaf 4 during the steady growth stage shows a sigmoidal pattern along the leaf axis for both treatments. Although salinity did not affect or even increased the length of the epidermal cells in some locations in the growth zone compared to the control treatment, the final length of the epidermal cells was reduced by 14% at 120 mmol/L NaCl. Thus, we concluded that the observed reduction in the leaf elongation rate derived in part from the reduced cell division rate and either the shortened cell elongation zone or shortened duration of cell elongation. This suggests that more attention should be paid to the effects of salinity on those properties of cell production and the period of cell maturation that are related to the properties of cell wall. [source] Nutritional physiology and colony form in Podocoryna carnea (Cnidaria: Hydrozoa)INVERTEBRATE BIOLOGY, Issue 4 2008Dirk Bumann Abstract. We compared growth rates and final morphological states of the athecate colonial hydroid Podocoryna carnea in two nutritional environments: one varying the quantity of food provided at a fixed interval and the second varying the time between feedings of a fixed quantity. In both environments, replicate colonies were either fed uniformly, or fed on only one side and starved on the other. In addition, we fed colonies fluorescence-labeled cultures of Artemia salina and documented the subsequent distribution of label. We found that both the growth rates and the final morphological state varied logarithmically with food supply. Heterogeneous feeding had a marked effect on colony morphology, with a sharp boundary in polyp number, stolon density, and polyp size forming at the fed,unfed interface. The distribution of fluorescence was correlated with sites of colony growth. These results confirm and extend early work on the priority of growth zones in colonial hydroids, and present new challenges for understanding the relationship among energy metabolism, gastrovascular circulation, and colony form. [source] Validation of roughhead grenadier (Macrourus berglax) otolith readingJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2 2002E. Rodríguez-Marín Roughhead grenadier Macrourus berglax Lacépède 1802, is becoming an important commercial fish in the north-west Atlantic fisheries and reliable age information is needed for its assessment. Macrourus berglax has been aged by counting otolith growth zones assumed to represent anulli. Three validation methods were applied: back-calculation of length-at-age, length,frequency analysis, and analyses of the progression of the length mode of an exceptionally large year class. Results on size-at-age estimated by otolith growth zone counts, length,frequency analysis of pre-anal fin length and modal progression were internally consistent, but estimates by back-calculation were different. This latter method produces unrealistic growth curves for each sex due to the weak relationship between otolith size as measured and pre-anal fin length. Up to age 8,9 the size-at-age were the same for males and females; thereafter males were smaller than females. Male growth rate declined when pre-anal fin length reached 18 cm at around age 9, whereas the growth of females started to decline at about 30 cm at around age 16. The Von Bertalanffy growth model derived from otolith analysis was similar to that obtained by the Multifan length frequency analysis model, and gave realistic values of Linf, close to the maximum anal fin lengths found in catches. The results showed that Macrourus berglax has a prolonged life cycle and differences in growth between males and females. [source] Prograde metamorphic sequence of REE minerals in pelitic rocks of the Central Alps: implications for allanite,monazite,xenotime phase relations from 250 to 610 °CJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2008E. JANOTS Abstract The distribution of REE minerals in metasedimentary rocks was investigated to gain insight into the stability of allanite, monazite and xenotime in metapelites. Samples were collected in the central Swiss Alps, along a well-established metamorphic field gradient that record conditions from very low grade metamorphism (250 °C) to the lower amphibolite facies (,600 °C). In the Alpine metapelites investigated, mass balance calculations show that LREE are mainly transferred between monazite and allanite during the course of prograde metamorphism. At very low grade metamorphism, detrital monazite grains (mostly Variscan in age) have two distinct populations in terms of LREE and MREE compositions. Newly formed monazite crystallized during low-grade metamorphism (<440 °C); these are enriched in La, but depleted in Th and Y, compared with inherited grains. Upon the appearance of chloritoid (,440,450 °C, thermometry based on chlorite,choritoid and carbonaceous material), monazite is consumed, and MREE and LREE are taken up preferentially in two distinct zones of allanite distinguishable by EMPA and X-ray mapping. Prior to garnet growth, allanite acquires two growth zones of clinozoisite: a first one rich in HREE + Y and a second one containing low REE contents. Following garnet growth, close to the chloritoid,out zone boundary (,556,580 °C, based on phase equilibrium calculations), allanite and its rims are partially to totally replaced by monazite and xenotime, both associated with plagioclase (± biotite ± staurolite ± kyanite ± quartz). In these samples, epidote relics are located in the matrix or as inclusions in garnet, and these preserve their characteristic chemical and textural growth zoning, indicating that they did not experience re-equilibration following their prograde formation. Hence, the partial breakdown of allanite to monazite offers the attractive possibility to obtain in situ ages, representing two distinct crystallization stages. In addition, the complex REE + Y and Th zoning pattern of allanite and monazite are essential monitors of crystallization conditions at relatively low metamorphic grade. [source] Characterization of polymetamorphism in the Austroalpine basement east of the Tauern Window using garnet isopleth thermobarometryJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2006F. GAIDIES Abstract Garnet in metapelites from the Wölz and Rappold Complexes of the Austroalpine basement east of the Tauern Window typically shows two distinct growth zones. A first garnet generation usually forms the cores of garnet porphyroblasts and is separated by a prominent microstructural and chemical discontinuity from a second garnet generation, which forms rims of variable width. Whereas the rims were formed during the Eo-Alpine metamorphic overprint, the garnet cores represent remnants of at least two pre-Eo-Alpine metamorphic events. The pressure and temperature estimates obtained from garnet isopleth thermobarometry applied to the first growth increments of the pre-Eo-Alpine garnet cores from the Wölz and Rappold Complexes cluster into two distinct domains: (i) in the Wölz Complex, incipient growth of the first-generation garnet occurred at 4 ± 0.5 kbar and 535 ± 20 °C, (ii) in the Rappold Complex, incipient growth of the oldest garnet cores took place at 5.3 ± 0.3 kbar and 525 ± 15 °C. The Eo-Alpine garnet generation started to grow at 6.5 ± 0.5 kbar and 540 ± 10 °C. According to radiometric dating, the low-pressure garnet from the Wölz complex was formed during a Permian metamorphic event. The first-generation garnet of the Rappold Complex is probably of Variscan age. [source] | |||||||||||||