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Morphological Plasticity (morphological + plasticity)
Selected AbstractsPerformance Trade-offs Driven by Morphological Plasticity Contribute to Habitat Specialization of Bornean Tree SpeciesBIOTROPICA, Issue 4 2009Daisy H. Dent ABSTRACT Growth-survival trade-offs play an important role in niche differentiation of tropical tree species in relation to light-gradient partitioning. However, the mechanisms that determine differential species performance in response to light and soil resource availability are poorly understood. To examine responses to light and soil nutrient availability, we grew seedlings of five tropical tree species for 12 mo at < 2 and 18 percent full sunlight and in two soil types representing natural contrasts in nutrient availability within a lowland dipterocarp forest in North Borneo. We chose two specialists of nutrient-rich and nutrient-poor soils, respectively, and one habitat generalist. Across all species, growth was higher in high than low light and on more nutrient rich soil. Although species differed in growth rates, the ranking of species, in terms of growth, was consistent across the four treatments. Nutrient-rich soils improved seedling survival and increased growth of three species even under low light. Slower-growing species increased root allocation and reduced specific leaf area (SLA) and leaf area ratio (LAR) in response to decreased nutrient supply. All species increased LAR in response to low light. Maximum growth rates were negatively correlated with survival in the most resource-limited environment. Nutrient-poor soil specialists had low maximum growth rates but high survival at low resource availability. Specialists of nutrient-rich soils, plus the habitat generalist, had the opposite suite of traits. Fitness component trade-offs may be driven by both light and belowground resource availability. These trade-offs contribute to differentiation of tropical tree species among habitats defined by edaphic variation. [source] Nutrient limitation and morphological plasticity of the carnivorous pitcher plant Sarracenia purpurea in contrasting wetland environmentsNEW PHYTOLOGIST, Issue 3 2008Terry Bott Summary ,,Plasticity of leaf nutrient content and morphology, and macronutrient limitation were examined in the northern pitcher plant, Sarracenia purpurea subsp. purpurea, in relation to soil nutrient availability in an open, neutral pH fen and a shady, acidic ombrotrophic bog, over 2 yr following reciprocal transplantation of S. purpurea between the wetlands. ,,In both wetlands, plants were limited by nitrogen (N) but not phosphorus (P) (N content < 2% DW,1, N : P < 14) but photosynthetic quantum yields were high (FV/FM > 0.79). Despite carnivory, leaf N content correlated with dissolved N availability to plant roots (leaf N vs , r2 = 0.344, P < 0.0001); carnivorous N acquisition did not apparently overcome N limitation. ,,Following transplantation, N content and leaf morphological traits changed in new leaves to become more similar to plants in the new environment, reflecting wetland nutrient availability. Changes in leaf morphology were faster when plants were transplanted from fen to bog than from bog to fen, possibly reflecting a more stressful environment in the bog. ,,Morphological plasticity observed in response to changes in nutrient supply to the roots in natural habitats complements previous observations of morphological changes with experimental nutrient addition to pitchers. [source] Morphological plasticity of Parrotia persica leaves in eastern Hyrcanian forests (Iran) is related to altitudeNORDIC JOURNAL OF BOTANY, Issue 3 2010Hamed Yosefzadeh Variation in leaf characters of Parrotia persica in relation to their position in the canopy along an altitudinal gradient were studied. Genetic and phenotypic characters make P. persica one of the most noteworthy plants in the five floristic regions of Iran. It is an endemic species of the Hyrcanian forests, and occurs naturally from sea level to over 900 m a.s.l. on the north side of the Mountain Ranges of Alborz, northern Iran. There was a significant effect of altitude only on few leaf features [width of lamina, base angle (internal angle of lamina), number of pair vein (number of principal veins of lamina) of leaf, top and end of leaf figure]. Among different geographical sides of the crown, there was no significant difference in the plasticity of leaf features, but leaf figure (both top of leaf figure and end of leaf figure) showed the lowest plasticity among the different leaf characters. Of all characters measured, the lowest plasticity among the three populations was found for base angle and number of vein pairs. A PCA analysis showed that leaf petiole and maximum width of lamina in 0.9 of its length, together with leaf figure and width of lamina, accounted for the greatest variation in difference of populations. [source] Adaptive modifications of carapace outlines in the Cytheroidea (Ostracoda: Crustacea)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2009GENGO TANAKA Shell outlines of 202 extant cytheroidean ostracods were analysed in dorsal, lateral, and posterior views by elliptic Fourier analysis. The results obtained confirm that the exterior morphology is related to ecological factors as well as phylogenetic constraints. Phytal species living on tall seagrass and benthic species burrowing in sediments are characterized and differentiated from the species crawling on sediments by the presence of slender shells with tapered venters. With reference to reconstruction of ancestral state of outline traits on the molecular phylogeny, the hypothetical ancestor of cytheroidean ostracods is presumed to have had an average-shaped shell. Morphological plasticity of the shell outline was observed in many families. The phytal species living on tall seagrass appear to have evolved convergently with species from other habitats, acquiring slim shell outlines during the Cenozoic period. The present analysis also reveals the phylogenetic constraints on the morphological evolution of the Trachyleberididae in their adaptation to a burrowing habit. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 810,821. [source] Induction of rapid, activity-dependent neuronal,glial remodelling in the adult rat hypothalamus in vitroEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2003Sarah L. Langle Abstract The hypothalamic oxytocinergic system offers a remarkable model of morphological plasticity in the adult because its neurons and astrocytes undergo mutual remodelling in relation to differing physiological conditions. Among various factors involved in such plasticity, oxytocin (OT) itself appears of primary importance as its central administration resulted in morphological changes similar to those brought on by physiological stimuli. In the present study, we applied OT on acute hypothalamic slices from adult rats that included the supraoptic nucleus. Using ultrastructural morphometric analyses, we found that it induced a significant reduction of astrocytic coverage of OT neurons, leaving their surfaces directly juxtaposed, to an extent similar to that detected in vivo under conditions like lactation. These neuronal,glial changes were rapid and reversible, occurring within a few hours, and specifically mediated via OT receptors. They were potentiated by oestrogen and depended on calcium mobilization and de novo protein synthesis. Moreover, they depended on concurrent neuronal activation brought on by hyperosmotic stimulation or blockade of inhibitory GABAergic neurotransmission; they were inhibited by blockade of glutamatergic receptors. Taken together, our observations show that intrahypothalamic release of OT affects not only neuronal activation of the OT system but its morphological plasticity as well. Moreover, the activity dependence of the OT-induced changes strongly suggests that astrocytes can sense the level of activity of adjacent neurons and/or afferent input and this can subsequently act as a signal to bring on the neuronal and glial conformational changes. [source] Repeated restraint stress suppresses neurogenesis and induces biphasic PSA-NCAM expression in the adult rat dentate gyrusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2003Kara Pham Abstract Chronic restraint stress has been shown to induce structural remodelling throughout the interconnected dentate gyrus-CA3 fields. To find out how this stressor affects the rate of adult hippocampal neurogenesis, we subjected rats to acute or chronic restraint stress and assessed the proliferation, survival and differentiation of newly born cells in the dentate gyrus. We also examined polysialylated neural cell adhesion molecule expression, a molecule normally expressed in immature neurons and important for morphological plasticity. The results show that acute restraint stress did not change either the proliferation of dentate gyrus precursor cells or the expression of polysialylated neural cell adhesion molecule, whereas 3 weeks of chronic restraint stress suppressed proliferation by 24% and increased polysialylated neural cell adhesion molecule expression by 40%. The study was extended for an additional 3 weeks to trace the survival and development of the cells born after the initial 3 weeks of restraint. Rats subjected to 6 weeks of daily restraint stress exhibited suppressed cell proliferation and attenuated survival of the recently born cells after the extended time course, resulting in a 47% reduction of granule cell neurogenesis. Furthermore, 6 weeks of chronic stress significantly reduced the total number of granule cells by 13% and the granule cell layer volume by 5%. Expression of polysialylated neural cell adhesion molecule followed a biphasic time course, displaying a significant up-regulation after 3 weeks of daily restraint stress that was lost after 6 weeks of stress. These studies may help us understand the basis for hippocampal shrinkage and raise questions about the ultimate reversibility of the effects of chronic stress. [source] Substance induced plasticity in noradrenergic innervation of the paraventricular hypothalamic nucleusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2003Arthur S. P. Jansen Abstract Single administration of the cytokine interleukin-1, (IL-1), or the psychostimulant amphetamine, enhanced adrenocorticotropin hormone and corticosterone responses to a stress challenge weeks later. This long-lasting hypothalamic-pituitary-adrenal (HPA)-sensitization is paralleled by an increase in electrically evoked release of noradrenaline in the paraventricular hypothalamic nucleus (PVN). We hypothesized that these functional changes may be associated with morphological plasticity of noradrenergic projections to the PVN, a parameter that shows high reproducibility. Specific alterations in relative (nor)adrenergic innervation density were studied by using dopamine-,-hydroxylase (DBH) as a marker. An image analysis system was used to detect changes in the relative DBH innervation density of the PVN. Groups of adult male rats were given IL-1 (10 µg/kg i.p.), amphetamine (5 mg/kg i.p.), or saline. Three weeks later, IL-1 and amphetamine primed rats showed enhanced adrenocorticotropin hormone and corticosterone responses to an amphetamine challenge. In another set of experiments, the relative DBH innervation density was measured in different PVN subnuclei at four rostro-caudal levels. Single administration of either IL-1 or amphetamine causes three weeks later a selective decrease in relative DBH innervation density in those subnuclei of the PVN that contain high numbers of corticotrophin-releasing hormone (CRH) producing neurons: the dorsal parvocellular and medial parvocellular PVN. We conclude that (1) long-lasting sensitization induced by single exposure to IL-1 and amphetamine induces specific pattern of neuroplastic changes in (nor)adrenergic innervation in the PVN and (2) reduction of relative DBH innervation density in CRH-rich areas is associated with paradoxical increase of electrically evoked release of (nor)adrenaline. [source] Verbreitung und Differenzierung der mitteleuropäischen Unterarten von Buglossoides arvensis (L.) I. M. Johnst. (Boraginaceae),FEDDES REPERTORIUM, Issue 1-2 2003A. Clermont In Mitteleuropa sind zwei Unterarten des Ackersteinsamens (Buglossoidesarvensis subsp. arvensis, B. arvensis subsp. sibthorpiana) verbreitet. Die molekularbiologische Untersuchung der nucleären ITS1-Region von 55 mitteleuropäischen Belegen verdeutlicht die Eigenständigkeit der beiden Sippen. Innerhalb des 238 Basenpaare langen Markers unterscheiden sich die Unterarten durch 15 Substitutionen (6,4 %). Die Ergebnisse lassen den Schluss zu, dass die Unterarten bisher aufgrund ihrer morphologischen Plastizität oft verwechselt und Häufigkeit und Verbreitung der Subspecies sibthorpiana unterschätzt wurden. Morphologisch lassen sich die beiden Unterarten anhand folgender Merkmale unterscheiden: Buglossoides arvensis subsp. arvensis besitzt längliche Keimblätter, eine gerade Gynobasis, einen unverdickten, geraden Pedicellus sowie cremefarbene oder selten leicht rosa gefärbte Blüten. Buglossoides arvensis subsp. sibthorpiana zeichnet sich durch runde Keimblätter, eine zur Fruchtzeit leicht zur Blütenstandsachse geneigte Gynobasis, einen schiefen, verdickten Pedicellus an den unteren Früchten und blaue, rosa oder cremefarben gefärbte Blüten aus. Weiterhin unterscheiden sich die Unterarten in ihren ökologischen Ansprüchen: B. arvensis subsp. arvensis kommt nur als Ackerunkraut vor, B. arvensis subsp. sibthorpiana wächst sowohl auf Ackerstandorten als auch auf Trockenrasen, sandigen Ruderalflächen oder in trockenen, lichten Wäldern. Distribution and differentiation of the Central European subspecies of Buglossoides arvensis (L.) I.M.Johnst. (Boraginaceae) The Corn Gromwell (Buglossoides arvensis) has two Central European subspecies, B. arvensis subsp. arvensis and B. arvensis subsp. sibthorpiana. The ITS1-region of 55 European samples was amplified and sequenced and it yielded a 238 bp fragment, which consistently differed by 15 substitutions between the two subspecies. The results suggest that the two subspecies indeed represent two independent taxa and have been confused mainly because of their morphological plasticity. Because of this confusion, distribution and abundance were poorly understood. The subspecies as here re-defined can be distinguished as follows: B. arvensis subsp. arvensis has oblong cotyledons, a horizontal gynobase, an unthickened pedicel in fruit, and a cream-coloured corolla. B. arvensis subsp. sibthorpiana has circular cotyledons, an oblique gynobase, an obliquely thickened pedicel in fruit, and a light blue to (more rarely) cream-coloured corolla. The two taxa show some degree of ecological differentiation: B. arvensis subsp. arvensis is only found as a weed in winter cereals, whereas B. arvensis subsp. sibthorpiana is occasionally found as a weed in fields, but also on dry grasslands, sandy waste sites and road sides, and in dry, open forests. [source] Differential erbB signaling in astrocytes from the cerebral cortex and the hypothalamus of the human brainGLIA, Issue 4 2009Ariane Sharif Abstract Studies in rodents have shown that astroglial erbB tyrosine kinase receptors are key regulatory elements in neuron,glia communication. Although both astrocytes and deregulation of erbB functions have been implicated in the pathogenesis of many common human brain disorders, erbB signaling in native human brain astrocytes has never been explored. Taking advantage of our ability to perform primary cultures from the cortex and the hypothalamus of human fetuses, we conducted a thorough analysis of erbB signaling in human astrocytes. We showed that human cortical astrocytes express erbB1, erbB2, and erbB3, whereas human hypothalamic astrocytes express erbB1, erbB2, and erbB4 receptors. Ligand-dependent activation of different erbB receptor heterodimeric complexes in these two populations of astrocytes translated into different morphological and proliferative responses. Although morphological plasticity was more pronounced in hypothalamic astrocytes than in cortical astrocytes, the former showed a lower mitogenic potential. Decreasing erbB4 expression via siRNA-mediated gene knockdown revealed that erbB4 constitutively restrains basal proliferative activity in hypothalamic astrocytes. We further show that treatment of human astrocytes with a protein kinase C activator results in rapid tyrosine phosphorylation of erbB receptors that involves cleavage of endogenous membrane bound erbB ligands by metalloproteinases. Together, these results indicate that erbB signaling in primary human brain astrocytes is functional, region-specific, and can be activated in a paracrine and/or autocrine manner. In addition, by revealing that some aspects of astroglial erbB signaling are different between human and rodents, our results provide a molecular framework to explore the potential involvement of astroglial erbB signaling deregulation in human brain disorders. © 2008 Wiley-Liss, Inc. [source] Morphometric comparison of the cephalic region of cultured Acipenser baerii (Brandt, 1869), Acipenser naccarii (Bonaparte, 1836) and their hybrid,JOURNAL OF APPLIED ICHTHYOLOGY, Issue 1 2006C. Costa Summary Geometric morphometric techniques were used in the characterization of morphological differences of the cranial region in cultured Acipenser baerii and A. naccarii and their hybrid. Species identification in sturgeons sometimes is difficult, because of the morphological plasticity of individual variability and the small differences between taxa. Identification is also complicated by human intervention and manipulation (e.g. aquaculture, hybridization, pollution). This study indicates how the differences between two species and their hybrids can be quantified and accurately visualized via geometric morphometrics. This technique may serve as a useful methodology to supplement analytical studies on morphometrics and systematics in Acipenseridae. [source] Myogenesis in Aplysia californica (Cooper, 1863) (Mollusca, Gastropoda, Opisthobranchia) with special focus on muscular remodeling during metamorphosisJOURNAL OF MORPHOLOGY, Issue 7 2008Tim Wollesen Abstract To date only few comparative approaches tried to reconstruct the ontogeny of the musculature in invertebrates. This may be due to the difficulties involved in reconstructing three dimensionally arranged muscle systems by means of classical histological techniques combined with light or transmission electron microscopy. Within the scope of the present study we investigated the myogenesis of premetamorphic, metamorphic, and juvenile developmental stages of the anaspidean opisthobranch Aplysia californica using fluorescence F-actin-labeling in conjunction with modern confocal laser scanning microscopy. We categorized muscles with respect to their differentiation and degeneration and found three true larval muscles that differentiate during the embryonic and veliger phase and degenerate during or slightly after metamorphosis. These are the larval retractor, the accessory larval retractor, and the metapodial retractor muscle. While the pedal retractor muscle, some transversal mantle fibers and major portions of the cephalopedal musculature are continued and elaborated during juvenile and adult life, the buccal musculature and the anterior retractor muscle constitute juvenile/adult muscles which differentiate during or after metamorphosis. The metapodial retractor muscle has never been reported for any other gastropod taxon. Our findings indicate that the late veliger larva of A. californica shares some common traits with veligers of other gastropods, such as a larval retractor muscle. However, the postmetamorphic stages exhibit only few congruencies with other gastropod taxa investigated to date, which is probably due to common larval but different adult life styles within gastropods. Accordingly, this study provides further evidence for morphological plasticity in gastropod myogenesis and stresses the importance of ontogenetic approaches to understand adult conditions and life history patterns. J. Morphol., 2008. © 2007 Wiley-Liss, Inc. [source] Regulation of dendritic spine morphology by an NMDA receptor-associated Rho GTPase-activating protein, p250GAPJOURNAL OF NEUROCHEMISTRY, Issue 4 2008Takanobu Nakazawa Abstract The NMDA receptor regulates spine morphological plasticity by modulating Rho GTPases. However, the molecular mechanisms for NMDA receptor-mediated regulation of Rho GTPases remain elusive. In this study, we show that p250GAP, an NMDA receptor-associated RhoGAP, regulates spine morphogenesis by modulating RhoA activity. Knock-down of p250GAP increased spine width and elevated the endogenous RhoA activity in primary hippocampal neurons. The increased spine width by p250GAP knock-down was suppressed by the expression of a dominant-negative form of RhoA. Furthermore, p250GAP is involved in NMDA receptor-mediated RhoA activation. In response to NMDA receptor activation, exogenously expressed green fluorescent protein (GFP)-tagged p250GAP was redistributed. Thus, these data suggest that p250GAP plays an important role in NMDA receptor-mediated regulation of RhoA activity leading to spine morphological plasticity. [source] Changes in survivorship, behavior, and morphology in native soft-shell clams induced by invasive green crab predatorsMARINE ECOLOGY, Issue 3 2010W. Lindsay Whitlow Abstract Many studies on invasive species show reduced native densities, but few studies measure trait-mediated effects as mechanisms for changes in native growth rates and population dynamics. Where native prey face invasive predators, mechanisms for phenotypic change include selective predation, or induced behavioral or morphological plasticity. Invasive green crabs, Carcinus maenas, have contributed to declines in native soft-shell clams, Mya arenaria, in coastal New England, USA. We tested the hypothesis that clam ability to detect chemical cues from predators or damaged conspecifics would induce greater burrowing depth as a refuge from invasive crabs, and greater burrowing would require increased siphon growth. To determine how crab predation affected clam survivorship and phenotypic traits in the field, clams in exclosure, open, and crab enclosure plots were compared. Crab predation reduced clam density, and surviving clams were deeper and larger, with longer siphons. To determine whether the mechanism for these results was selective predation or induced plasticity, phenotypes were compared between clams exposed to chemical cues from crab predation and clams exposed to seawater in laboratory and field experiments. In response to crab predation cues, clams burrowed deeper, with longer siphons and greater siphon mass. Overall, crab predation removed clams with shorter siphons at shallow depths, and crab predation cues induced greater burrowing depths and longer siphons. Longer siphons and greater siphon mass of deeper clams suggests clams may allocate energy to siphon growth in response to crabs. By determining native behavior and morphological changes in response to an invasive predator, this study adds to our understanding of mechanisms for invasive impacts and illustrates the utility of measuring trait-mediated effects to investigate predator,prey dynamics. [source] Nutrient limitation and morphological plasticity of the carnivorous pitcher plant Sarracenia purpurea in contrasting wetland environmentsNEW PHYTOLOGIST, Issue 3 2008Terry Bott Summary ,,Plasticity of leaf nutrient content and morphology, and macronutrient limitation were examined in the northern pitcher plant, Sarracenia purpurea subsp. purpurea, in relation to soil nutrient availability in an open, neutral pH fen and a shady, acidic ombrotrophic bog, over 2 yr following reciprocal transplantation of S. purpurea between the wetlands. ,,In both wetlands, plants were limited by nitrogen (N) but not phosphorus (P) (N content < 2% DW,1, N : P < 14) but photosynthetic quantum yields were high (FV/FM > 0.79). Despite carnivory, leaf N content correlated with dissolved N availability to plant roots (leaf N vs , r2 = 0.344, P < 0.0001); carnivorous N acquisition did not apparently overcome N limitation. ,,Following transplantation, N content and leaf morphological traits changed in new leaves to become more similar to plants in the new environment, reflecting wetland nutrient availability. Changes in leaf morphology were faster when plants were transplanted from fen to bog than from bog to fen, possibly reflecting a more stressful environment in the bog. ,,Morphological plasticity observed in response to changes in nutrient supply to the roots in natural habitats complements previous observations of morphological changes with experimental nutrient addition to pitchers. [source] Leaf photoacclimatory responses of the tropical seagrass Thalassia testudinum under mesocosm conditions: a mechanistic scaling-up studyNEW PHYTOLOGIST, Issue 1 2007Napo M. Cayabyab Summary ,,Here, the leaf photoacclimatory plasticity and efficiency of the tropical seagrass Thalassia testudinum were examined. ,,Mesocosms were used to compare the variability induced by three light conditions, two leaf sections and the variability observed at the collection site. ,,The study revealed an efficient photosynthetic light use at low irradiances, but limited photoacclimatory plasticity to increase maximum photosynthetic rates (Pmax) and saturation (Ek) and compensation (Ec) irradiances under high light irradiance. A strong, positive and linear association between the percentage of daylight hours above saturation and the relative maximum photochemical efficiency (FV/FM) reduction observed between basal and apical leaf sections was also found. ,,The results indicate that T. testudinum leaves have a shade-adapted physiology. However, the large amount of heterotrophic biomass that this seagrass maintains may considerably increase plant respiratory demands and their minimum quantum requirements for growth (MQR). Although the MQR still needs to be quantified, it is hypothesized that the ecological success of this climax species in the oligotrophic and highly illuminated waters of the Caribbean may rely on the ability of the canopy to regulate the optimal leaf light environment and the morphological plasticity of the whole plant to enhance total leaf area and to reduce carbon respiratory losses. [source] Growth rate constrain morphological divergence when driven by competitionOIKOS, Issue 1 2006Jens Olsson Resource competition has been hypothesized to be important in driving divergence by natural selection. The effect of competition on morphological divergence and plasticity has however rarely been investigated. Since low growth rates might constrain morphological modulation and individual growth rates usually are negatively related to the intensity of competition, there might be a connection between competition, growth rate and morphological divergence. We performed an aquarium experiment with young-of-the-year Eurasian perch (Perca fluviatilis L.) to investigate how individual growth rate affected morphological plasticity induced by contrasting habitat treatments. Furthermore, in a field study of 10 lakes we also related the degree of morphological differentiation between habitats to the intraspecific competitior biomass. In the aquarium experiment we found that morphological plasticity was growth rate dependent in that morphological differentiation between the habitat treatments was confined to high individual growth rates. In the field study we found that morphological differentiation between habitats decreased with increasing intraspecific competitior biomass. Since plasticity is hypothesized to be important in divergence and intraspecific biomass could serve as a proxy for the level of competition, we suggest that our results indicate that morphological divergence might be constrained during periods of intense intraspecific competition due to low growth rates. A possible scenario is that at low growth rates all energy available is used for metabolic maintenance and no surplus energy is therefore available for morphological modulation. [source] Chloroplast rotation and morphological plasticity of the unicellular alga Rhodosorus (Rhodophyta, Stylonematales)PHYCOLOGICAL RESEARCH, Issue 3 2002Sarah Wilson SUMMARY Time-lapse videomicroscopy was used to film chloroplast rotation in the 13 isolates of Rhodosorus marinus Geitler and one isolate of Rhodosorus magnei Fresnel & Billard maintained in culture. Cell diameter, rates of chloroplast rotation and the number of chloroplast lobes were measured in all isolates. Chloroplast rotation is a definitive characteristic of the genus Rhodosorus and should be included in its taxonomic description. Isolates of the type species, R. marinus, measure 4,7 ,m in diameter in low light (2,4 ,mol photons m,2 s,1) and 4.5,11.5 ,m in diameter in bright light (15,20 ,mol photons m,2 s,1), and have two to seven chloroplast lobes. Rhodosorus magnei is 9 ,m in diameter and has seven to nine chloroplast lobes in bright light. However, these cells are much smaller (approx. 4 ,m diam.) and have only two to three chloroplast lobes when maintained in low light. The species R. magnei was created based on its larger cell size and numerous chloroplast lobes compared with R. marinus, but since these characteristics were found to be quite variable and dependant on culture conditions, they cannot be used to differentiate these two species. [source] Differential expression of p120 catenin in glial cells of the adult rat brainTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 1 2004Norbert Chauvet Abstract p120 catenin (p120ctn) is involved in the regulation of cadherin-mediated adhesion and the dynamic organization of the actin cytoskeleton by modulating RhoGTPase activity. We have previously described the distribution of p120ctn during rat brain development and provided substantial evidence for the potential involvement of p120ctn in morphogenetic events and plasticity in the central nervous system. Here, we analyzed the cellular and ultrastructural distribution of p120ctn in glial cells of the adult rat forebrain. The highest intensity of immunostaining for p120ctn was found in cells of the choroid plexus and ependyma and was mainly restricted to the plasma membrane. However, p120ctn was almost absent from astrocytes. In contrast, in tanycytes, a particular glial cell exhibiting remarkable morphological plasticity, p120ctn, was localized at the plasma membrane and also in the cytoplasm. We show that a large subpopulation of oligodendrocytes expressed multiple isoforms, whereas other neural cells predominantly expressed isoform 1, and that p120ctn immunoreactivity was distributed through the cytoplasm and at certain portions of the plasma membrane. Finally, p120ctn was expressed by a small population of cortical NG2-expressing cells, whereas it was expressed by a large population of these cells in the white matter. However, in both regions, proliferating NG2-positive cells consistently expressed p120ctn. The expression of p120ctn by cells of the oligodendrocyte lineage suggests that p120ctn may participate in oligodendrogenesis and myelination. Moreover, the expression of p120ctn by various cell types and its differential subcellular distribution strongly suggest that p120ctn may serve multiple functions in the central nervous system. J. Comp. Neurol. 479:15,29, 2004. © 2004 Wiley-Liss, Inc. [source] Systematics and phylogeography of a threatened tortoise, the speckled padloperANIMAL CONSERVATION, Issue 3 2010S. R. Daniels Abstract This study investigated the systematics and phylogeography of a threatened tortoise of South Africa, the speckled padloper Homopus signatus. Sixty three specimens were collected from 17 localities that covered the distributional range of the two subspecies in western South Africa and a north-eastern population that was recently discovered near Pofadder. The Pofadder sample could not be assigned to either subspecies based on morphology. The samples were sequenced for two partial mtDNA fragments, nicotinamide adenine dinucleotide dehydrogenase component four and cytochrome b, which yielded ,1.1 kb, while a subset of the samples were sequenced for a 390 bp nuclear DNA (nDNA) fragment of prolactin. Phylogenetic analyses of mtDNA using minimum evolution, maximum parsimony and Bayesian inferences supported the monophyly of H. signatus and revealed that the Pofadder specimen was basal in the topology and sister to the remainder. The phylogenetic analyses did not support the recognition of two subspecies; there was statistical support for a Homopus signatus signatus clade but Homopus signatus cafer was not monophyletic. The nDNA analysis showed no difference between the subspecies and placed the Pofadder sample distant but not distinct from H. s. signatus. The mtDNA and the nDNA data suggest that the subspecies are invalid taxonomic units. The structure of the mtDNA network corresponded to the geographical distribution of populations. The north-western populations formed one haplocluster, corresponding to H. s. signatus, whereas the south-western populations formed three haploclusters, corresponding to H. s. cafer. The Pofadder sample was unconnected to the network. The morphology of the northern and southern morphotypes probably reflects selection for crypsis on the different substrate types of the regions, granites and sedimentary rocks, respectively. These results highlight that subspecies designations should be authenticated by molecular techniques because morphological plasticity can obfuscate phylogenetic relationships. We consider the western H. signatus populations as one taxonomic unit and recommend wider sampling of the Pofadder locality to clarify the taxonomic status of this lineage. [source] | |||||||||||||||||||||||||