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At least 19 recordsLinked to original sources

PubMed2000

Extracting species trees from complex gene trees: reconciled trees and vertebrate phylogeny.

Paralogy is a pervasive problem in trying to use nuclear gene sequences to infer species phylogenies. One strategy for dealing with this problem is to infer species phylogenies from gene trees using reconciled trees, rather than directly from the sequences themselves. In this approach, the optimal species tree is the tree that requires the fewest gene duplications to be invoked. Because reconciled trees can identify orthologous from paralogous sequences, there is no need to do this prior to the analysis. Multiple gene trees can be analyzed simultaneously; however, the problem of nonuniform gene sampling raises practical problems which are discussed. In this paper the technique is applied to phylogenies for nine vertebrate genes (aldolase, alpha-fetoprotein, lactate dehydrogenase, prolactin, rhodopsin, trypsinogen, tyrosinase, vassopressin, and Wnt-7). The resulting species tree shows much similarity with currently accepted vertebrate relationships.

Animals↗

PubMed2006

A whole-tree chamber system for examining tree-level physiological responses of field-grown trees to environmental variation and climate change.

A whole-tree chamber (WTC) system was installed at Flakaliden in northern Sweden to examine the long-term physiological responses of field-grown 40-year-old Norway spruce trees [Picea abies (L.) Karst.] to climate change. The WTCs were designed as large cuvettes to allow the net tree-level CO(2) and water fluxes to be measured on a continuous basis. A total of 12 WTCs were used to impose combinations of atmospheric carbon dioxide concentration, [CO(2)], and air temperature treatments. The air inside the ambient and elevated [CO(2)] WTCs was maintained at 365 and 700 micromol mol(-1), respectively. The air temperature inside the ambient temperature WTCs tracked air temperature outside the WTCs. Elevated temperatures were altered on a monthly time-step and ranged between +2.8 and +5.6 degrees C above ambient temperature. The system allowed continuous, long-term measurement of whole-tree photosynthesis, night-time respiration and transpiration. The performance of the WTCs was assessed using winter and spring data sets. The ability of the WTC system to measure tree-level physiological responses is demonstrated. All WTCs displayed a high level of control over tracking of air temperatures. The set target of 365 micromol mol(-1) in the ambient [CO(2)] chambers was too low to be maintained during winter because of tree dormancy and the high natural increase in [CO(2)] over winter at high latitudes such as the Flakaliden site. Accurate control over [CO(2)] in the ambient [CO(2)] chambers was restored during the spring and the system maintained the elevated [CO(2)] target of 700 micromol mol(-1) for both measurement periods. Air water vapour deficit (VPD) was accurately tracked in ambient temperature WTCs. However, as water vapour pressure in all 12 WTCs was maintained at the level of non-chambered (reference) air, VPD of elevated temperature WTCs was increased.

Carbon Dioxide↗

PubMed1999

Free-Tree--freeware program for construction of phylogenetic trees on the basis of distance data and bootstrap/jackknife analysis of the tree robustness. Application in the RAPD analysis of genus Frenkelia.

The Win95 program for computation of distance matrixes and construction of phylogenetic or phenetic trees on the basis of RAPD, RFLP and allozyme data was presented. In contrast with other presently available software, the program FreeTree can also assess the robustness of the tree topology by bootstrap, jackknife or OTU-jackknife analysis. Moreover, the program can be used also for an analysis of data obtained in several independent experiments performed with nonidentical subsets of taxa. The function of the program was demonstrated by an analysis of RAPD data from 22 strains of Frenkelia. The program is available as an autoextractive archive containing the installation files of FreeTree and TreeView, manual in MS Word format and a sample of the input file at http://www.natur.cuni.cz/flegr/programs/+ ++freetree.

Animals↗

PubMedDate not supplied

Determining water use by trees and forests from isotopic, energy balance and transpiration analyses: the roles of tree size and hydraulic lift.

Use of soil water and groundwater by open-grown Acer saccharum Marsh. (sugar maple) tree canopies and forests was estimated by measuring transpiration (E) rates using porometry, sap flow methods, and the Bowen ratio method. The Bowen ratio and sap flow methods showed the best agreement; porometer measurements scaled to whole canopies always underestimated E by 15-50%. Trees of different sizes showed very different rates of E. I hypothesized that these differences were due to the differential access of large and small trees to groundwater and soil water, respectively. Transpirational flux was partitioned between soil water and groundwater by tracing the water sources based on their hydrogen stable isotopic composition (deltaD). Soil water deltaD varied between -41 and -16 per thousand seasonally (May to September), whereas groundwater deltaD was -79 +/- 5 per thousand during the entire growing season. Daily transpiration rates of large (9-14 m tall) trees were significantly higher than those of small (3-5 m tall) trees (2.46-6.99 +/- 1.02-2.50 versus 0.69-1.80 +/- 0.39-0.67 mm day(-1)). Small trees also showed greater variation in E during the growing season than large trees. In addition, compared to the large trees, small trees demonstrated greater sensitivity to environmental factors that influence E, such as soil water deficits and increased evaporative demand. Over the entire growing season, large trees and forest stands composed of trees > 10 m tall transpired only groundwater. The high rates of water loss from large trees and older forests were likely a result of the influence of an enhanced "pool" of transpirational water in the upper soil layers caused by hydraulic lift (see Dawson 1993b). The hydraulically lifted water reservoir enabled large trees to use more potential transpirational water during daylight hours than small trees, leading to a greater total water flux. In contrast, small trees and forest stands composed of younger trees almost exclusively used soil water, except during two dry periods when their transpirational water was composed of between 7 and 17% groundwater. Thus groundwater discharge from sugar maple trees and forest stands of different sizes (ages) differs significantly, and large trees and older forest stands have a greater impact on the hydrologic balance of groundwater than small trees and younger forest stands. However, mixed stands (small and large trees) may have a greater overall impact on the regional hydrologic balance than old stands, because trees in mixed stands draw on both soil water and groundwater reservoirs and thus can substantially increase total water discharge on scales from tens to hundreds of hectares.

Journal Article↗

PubMed2005

Autumn frost hardiness in Norway spruce plus tree progeny and trees of the local and transferred provenances in central Sweden.

Reforestation with provenances from locations remote from the planting site (transferred provenances) or the progeny of trees of local provenances selected for superior form and vigor (plus trees) offer alternative means to increase yield over that obtained by the use of seed from unselected trees of the local provenance. Under Swedish conditions, Norway spruce (Picea abies (L.) Karst.) of certain transferred provenances generally has an advantage in productivity relative to the local provenance comparable to that of progeny of plus trees. The aim of this study was to explore the extent to which productivity gains achieved by provenance transfer or the use of plus tree progeny are associated with reductions in autumn frost hardiness, relative to that of trees of the local provenance. In a field trial with 19-year-old trees in central Sweden, bud hardiness was tested on four occasions during the autumn of 2002. Trees of the local provenance were compared with trees of a south Swedish provenance originating 3 degrees of latitude to the south, a Belarusian provenance and the progeny of plus trees of local origin. The Belarusian provenance was the least hardy and the local provenance the most hardy, with plus tree progeny and the south Swedish provenance being intermediate in hardiness. Both the Belarusian provenance and the plus tree progeny were significantly taller than trees of the other populations. Within provenances, tree height was negatively correlated with autumn frost hardiness. Among the plus tree progeny, however, no such correlation between tree height and autumn frost hardiness was found. It is concluded that although the gain in productivity achieved by provenance transfer from Belarus was comparable to that achieved by using the progeny of plus trees of the local provenance, the use of trees of the Belarus provenance involved an increased risk of autumn frost damage because of later hardening.

Acclimatization↗

PubMed2002

Influence of tree internal nitrogen reserves on the response of beech (Fagus sylvatica) trees to elevated atmospheric carbon dioxide concentration.

We examined the influence of plant internal nitrogen (N) reserves on the response of 3-year-old beech (Fagus sylvatica L.) trees to elevated atmospheric CO2 concentration ([CO2]) in a dual 15N and 13C long-term labeling experiment. Trees were grown on sand and received either no N nutrition (-N treatment) or 4 mM N (+N treatment) for 1 year. The -N and +N pretreated trees were then placed in growth chambers and grown in 350 (ambient) or 700 ppm (elevated) of a 13CO2 atmosphere for 24 weeks. In all treatments, trees were supplied with 4 mM 15N during the experiment. Irrespective of tree N reserves, elevated [CO2] increased cumulative carbon (C) uptake by about 30% at Week 24 compared with that for trees in the ambient treatment. Elevated [CO2] also caused a shift in C allocation to belowground compartments, which was more pronounced in -N trees than in +N trees. In +N trees, belowground allocation of new C at Week 24 was 67% in ambient [CO2] compared with 70% in elevated [CO2]. The corresponding values for -N trees were 70 and 79%. The increase in C allocation in response to elevated [CO2] was most evident as an increase in belowground respiration; however, specific root respiration was unaffected by the CO2 or N treatments. Although elevated [CO2] increased root growth and belowground respiration, it had no effect on N uptake at Week 24. As a result of increased C uptake, N concentrations were decreased in trees in the elevated [CO2] treatment compared with trees in the ambient treatment in both N treatments. Partitioning of new N uptake was unaffected by elevated [CO2] in +N trees. In -N trees, however, N allocation to the stem decreased in response to elevated [CO2] and N allocation to fine roots increased, suggesting a reduction in the formation of N reserves in response to elevated [CO2]. We conclude that the response of beech trees to elevated [CO2] is affected by internal N status and that elevated [CO2] may influence the ability of the trees to form N reserves.

Carbon Dioxide↗

PubMed2006

Relation between individual tree mortality and tree characteristics in a polluted and non-polluted environment.

UNLABELLED: Data on individual tree mortality in relatively healthy (Berezinskiy biosphere reserve) and damaged (surroundings of the mineral fertilizer plant 'Achema') even-aged Scots pine (Pinus sylvestris L.) stands are presented. Tree size and competition intensity were found to be the most significant predictors of individual tree mortality in all age groups of the relatively healthy Scots pine stands, however, an essential reduction in the closeness of relations between the tree mortality rate and these variables was determined with the aging of stands. An exponential decrease in tree mortality probability with an increase of tree size is characteristic for trees suffering different competition intensity, however, this decrease becomes much more pronounced as the competition pressure increases. The relations of different tree and stand variables with tree mortality probability have been found to become much weaker in the polluted environment. An exponential increase in tree mortality probability with an increase of crown defoliation was characteristic of damaged Scots pine stands, however, the rate of the increase was different in different age and diameter classes. The impact of crown defoliation on tree mortality rate increased with the aging of stands. At the same defoliation level, individual tree mortality probability was much higher for smaller suppressed trees, however, a relative increase in tree mortality probability along with an increase of crown defoliation was more pronounced for dominant trees. CONCLUSION: a higher mortality of damaged (defoliated) trees should be considered while assessing losses in forest productivity in a polluted environment.

Air Pollutants↗

PubMed2000

Estimating water use by sugar maple trees: considerations when using heat-pulse methods in trees with deep functional sapwood.

Accurate estimates of sapwood properties (including radial depth of functional xylem and wood water content) are critical when using the heat pulse velocity (HPV) technique to estimate tree water use. Errors in estimating the volumetric water content (V(h)) of the sapwood, especially in tree species with a large proportion of sapwood, can cause significant errors in the calculations ofsap velocity and sap flow through tree boles. Scaling to the whole-stand level greatly inflates these errors. We determined the effects of season, tree size and radial wood depth on V(h) of wood cores removed from Acer saccharum Marsh. trees throughout 3 years in upstate New York. We also determined the effects of variation in V(h) on sap velocity and sap flow calculations based on HPV data collected from sap flow gauges inserted at four depths. In addition, we compared two modifications of Hatton's weighted average technique, the zero-step and zero-average methods, for determining sap velocity and sap flow at depths beyond those penetrated by the sap flow gauges. Parameter V(h) varied significantly with time of year (DOY), tree size (S), and radial wood depth (RD), and there were significant DOY x S and DOY x RD interactions. Use of a mean whole-tree V(h) value resulted in differences ranging from -6 to +47% for both sap velocity and sap flow for individual sapwood annuli compared with use of the V(h) value determined at the specific depth where a probe was placed. Whole-tree sap flow was 7% higher when calculated on the basis of the individual V(h) value compared with the mean whole-tree V(h) value. Calculated total sap flow for a tree with a DBH of 48.8 cm was 13 and 19% less using the zero-step and the zero-average velocity techniques, respectively, than the value obtained with Hatton's weighted average technique. Smaller differences among the three methods were observed for a tree with a DBH of 24.4 cm. We conclude that, for Acer saccharum: (1) mean V(h) changes significantly during the year and can range from nearly 50% during winter and early spring, to 20% during the growing season;(2) large trees have a significantly greater V(h) than small trees; (3) overall, V(h) decreases and then increases significantly with radial wood depth, suggesting that radial water movement and storage are highly dynamic; and (4) V(h) estimates can vary greatly and influence subsequent water use calculations depending on whether an average or an individual V(h) value for a wood core is used. For large diameter trees in which sapwood comprises a large fraction of total stem cross-sectional area (where sap flow gauges cannot be inserted across the entire cross-sectional area), the zero-average modification of Hatton's weighted average method reduces the potential for large errors in whole-tree and landscape water balance estimates based on the HPV method.

Journal Article↗

PubMed1997

From gene to organismal phylogeny: reconciled trees and the gene tree/species tree problem.

The processes of gene duplication, loss, and lineage sorting can result in incongruence between the phylogenies of genes and those of species. This incongruence complicates the task of inferring the latter from the former. We describe the use of reconciled trees to reconstruct the history of a gene tree with respect to a species tree. Reconciled trees allow the history of the gene tree to be visualized and also quantify the relationship between the two trees. The cost of a reconciled tree is the total number of duplications and gene losses required to reconcile a gene tree with its species tree. We describe the use of heuristic searches to find the species tree which yields the reconciled tree with the lowest cost. This method can be used to infer species trees from one or more gene trees.

Animals↗

PubMed2004

Tree scanning: a method for using haplotype trees in phenotype/genotype association studies.

We use evolutionary trees of haplotypes to study phenotypic associations by exhaustively examining all possible biallelic partitions of the tree, a technique we call tree scanning. If the first scan detects significant associations, additional rounds of tree scanning are used to partition the tree into three or more allelic classes. Two worked examples are presented. The first is a reanalysis of associations between haplotypes at the Alcohol Dehydrogenase locus in Drosophila melanogaster that was previously analyzed using a nested clade analysis, a more complicated technique for using haplotype trees to detect phenotypic associations. Tree scanning and the nested clade analysis yield the same inferences when permutation testing is used with both approaches. The second example is an analysis of associations between variation in various lipid traits and genetic variation at the Apolipoprotein E (APOE) gene in three human populations. Tree scanning successfully identified phenotypic associations expected from previous analyses. Tree scanning for the most part detected more associations and provided a better biological interpretative framework than single SNP analyses. We also show how prior information can be incorporated into the tree scan by starting with the traditional three electrophoretic alleles at APOE. Tree scanning detected genetically determined phenotypic heterogeneity within all three electrophoretic allelic classes. Overall, tree scanning is a simple, powerful, and flexible method for using haplotype trees to detect phenotype/genotype associations at candidate loci.

Alcohol Dehydrogenase↗

PubMed2002

The probability of topological concordance of gene trees and species trees.

The concordance of gene trees and species trees is reconsidered in detail, allowing for samples of arbitrary size to be taken from the species. A sense of concordance for gene tree and species tree topologies is clarified, such that if the "collapsed gene tree" produced by a gene tree has the same topology as the species tree, the gene tree is said to be topologically concordant with the species tree. The term speciodendric is introduced to refer to genes whose trees are topologically concordant with species trees. For a given three-species topology, probabilities of each of the three possible collapsed gene tree topologies are given, as are probabilities of monophyletic concordance and concordance in the sense of N. Takahata (1989), Genetics 122, 957-966. Increasing the sample size is found to increase the probability of topological concordance, but a limit exists on how much the topological concordance probability can be increased. Suggested sample sizes beyond which this probability can be increased only minimally are given. The results are discussed in terms of implications for molecular studies of phylogenetics and speciation.

Biological Evolution↗

PubMed2005

Response of the nitrogen isotopic composition of tree-rings following tree-clearing and land-use change.

Clear-cutting of forests affects the nitrogen cycle and the nitrogen isotopic composition of bioavailable ammonium and nitrate in the soil. Here, we have used nitrogen isotopic variations of tree-rings in red oak (Quercus rubra) and white oak (Quercus alba) as indicators of changes in the nitrogen cycle on a local scale. The delta15N values of late-wood from trees at two remnant forest stands in Ontario, Canada, that underwent large-scale tree-clearing and permanent land-use change at different times were measured. Trees from the perimeter of each stand record a marked 1.5-2.5 per thousand increase in the delta15N values of their tree-rings relative to the values in trees from the center of the stand, with the shift synchronous with the tree-clearing and land-use change. This shift was most likely due to increased rates of nitrification and nitrate leaching in the soil as a result of tree-clearing combined with permanent changes in hydrology and probable fertilizer use accompanying the change in land-use. Nitrogen concentration in tree-rings was not affected bytree-clearing and the associated change in land-use. These results indicate that changes in nitrogen cycling in forest ecosystems, whether due to climate change, land-use change, or other environmental changes (increased O3, other atmospheric pollutants, insects, etc.), can be faithfully monitored with nitrogen isotopic compositions of tree-rings and that dendrogeochemical analysis can be incorporated into studies of the effects of long-term anthropogenic effects on forest ecosystems.

Analysis of Variance↗

PubMed2006

Responses of crown development to canopy openings by saplings of eight tropical submontane forest tree species in Indonesia: a comparison with cool-temperate trees.

BACKGROUND AND AIMS: Growth in trunk height in canopy openings is important for saplings. How saplings increase height growth in canopy openings may relate to crown architectural constraints. Responses of crown development to canopy openings in relation to trunk height growth were studied for saplings (0.2-2.5 m tall) of eight tropical submontane forest tree species in Indonesia. The results of this study were also compared with those of temperate trees in northern Japan. METHODS: The crown architecture differed among the eight tropical species, i.e. they had sparsely to highly developed branching structures. Crown allometry was compared among the eight species in each canopy condition (closed canopy or canopy openings), and between closed canopy and canopy openings within a species. A general linear regression model was used to analyse how each species increases height growth rate in canopy openings. Crown allometry and its plasticity were compared between tropical and temperate trees by a nested analysis of covariance. KEY RESULTS: Tropical submontane trees had responses similar to cool-temperate trees, showing an increase in height in canopy openings, i.e. taller saplings of sparsely branched species increase height growth rates by increasing the sapling leaf area. Cool-temperate trees have a wider crown projection area and a smaller leaf area per crown projection area to avoid self-shading within a crown compared with tropical submontane trees. Plasticity of the crown projection area is greater in cool-temperate trees than in tropical submontane trees, probably because of the difference in leaf longevity. CONCLUSIONS: This study concluded that interspecific variation in the responses of crown development to canopy openings in regard to increasing height related to the species' branching structure, and that different life-forms, such as evergreen and deciduous trees, had different crown allometry and plasticity.

Indonesia↗

PubMed1997

Inferring species trees from gene trees: a phylogenetic analysis of the Elapidae (Serpentes) based on the amino acid sequences of venom proteins.

Toward the goal of recovering the phylogenetic relationships among elapid snakes, we separately found the shortest trees from the amino acid sequences for the venom proteins phospholipase A2 and the short neurotoxin, collectively representing 32 species in 16 genera. We then applied a method we term gene tree parsimony for inferring species trees from gene trees that works by finding the species tree which minimizes the number of deep coalescences or gene duplications plus unsampled sequences necessary to fit each gene tree to the species tree. This procedure, which is both logical and generally applicable, avoids many of the problems of previous approaches for inferring species trees from gene trees. The results support a division of the elapids examined into sister groups of the Australian and marine (laticaudines and hydrophiines) species, and the African and Asian species. Within the former clade, the sea snakes are shown to be diphyletic, with the laticaudines and hydrophiines having separate origins. This finding is corroborated by previous studies, which provide support for the usefulness of gene tree parsimony.

Animals↗

PubMed1976

Criteria for optimising phylogenetic trees and the problem of determining the root of a tree.

The process of determining the optimal phylogenetic tree from amino acid sequences or comparable data is divided into six stages. Particular attention is given both to the criteria that are used when testing for the optimal tree and the problem of determining the position of the original ancestor. Four types of criteria for evaluating the optimal tree are considered: 1. parsimony (fewest total changes), 2. path lengths from an ancestor to existing species, 3. subtracting the difference between each pair of species as measured on the tree and as compared directly with the data ("excess differences"), 4. Moore Residual Coefficient. These criteria are examined on a set of test data and some of the reasons for the differences among them are discussed. For example, the "average percent standard deviation" weights excess differences unequally in inverse proportion to the square of the observed differences. The Moore Residual Coefficient and the "excess differences" will not necessarily give a value of zero when there are no duplicated changes unless there can only be two states for each character (i.e. binary data). The path length and difference criteria (as well as the Moore Residual Coefficient) give unequal weighting to the individual branches of the tree by counting some branches more times than others. Particularly because of this some criteria will reject trees that are equally parsimonious and the criteria are said to be invalid. However the criterion of parsimony is insensitive in that it can give the same value for several basic networks and it does not specify the position of the original ancestor, the root of the tree. The importance is emphasised of stating a model and examining its predictions before a criterion is chosen to select the best network. The number of rooted trees that can be derived from a basic network (or unrooted tree) is described in relation to how detailed a description of the original ancestor is required. Four methods are described for determining the position of the root of the tree or original ancestor. Each method depends upon some additional information to that used in constructing the basic network and the method chosen will depend on this additional knowledge.

Animals↗

PubMed1998

Changes in the relationship between tree size and aboveground respiration in field-grown hinoki cypress (Chamaecyparis obtusa) trees over three years.

Respiration measurements of aerial parts of 18-year-old hinoki cypress (Chamaecyparis obtusa (Sieb. et Zucc.) Endl.) trees were made under field conditions over three years to study changing relationships with tree age between respiration and phytomass, phytomass increment, and leaf mass. The relationship between annual respiration (r(a)) and phytomass (w(T)) was approximated by a proportional function (r(a) = aw(T)), where the proportional constant (a) decreased year by year. The effect of time on the relationship between annual respiration and phytomass of each sample tree was fitted by a power function. Respiration of the tree suppressed by the canopy decreased year by year, but respiration of the other trees increased slightly with age. The relationship between annual respiration and leaf mass was also approximated by a generalized power function. Excluding the suppressed tree, the relationship between annual respiration (r(a)) and the annual increment of aboveground phytomass (Deltaw(T)) was described by a proportional function (r(a) = 2.27Deltaw(T)), where the proportional constant, 2.27, was independent of sample tree and year, indicating that about 2.3 times of the annual aboveground phytomass increment equivalent was respired annually. For any tree, the time constant relationships between annual respiration and leaf mass and phytomass increment for different-sized trees were similar to the corresponding time continuum relationships. In contrast, the time continuum relationship between annual respiration and phytomass differed from the time constant relationship, indicating that respiration of less active woody tissue contributed significantly to aboveground respiration. Based on the relationship between tree size and annual respiration, annual aboveground stand respiration was estimated to be 25.0, 26.9, and 25.8 Mg(dm) ha(-1) year(-1) for the three consecutive years, respectively, and the corresponding aboveground stand biomass was 60.0, 69.0, and 76.8 Mg(dm) ha(-1).

Journal Article↗

PubMed2000

A lectin-histochemical study on the seminiferous epithelium of the northern smooth-tailed tree shrew (Dendrogale murina) and the Java tree shrew (Tupaia javanica).

Lectin-binding patterns in the testes of the northern smooth-tailed tree shrew, Dendrogale murina and Java tree shrew, Tupaia javanica were studied by light microscopy and compared the data with those of the common tree shrew. Four lectins (PNA, SBA, BPA and GS-II) were used in this study. Peanut (Arachis hypogaea) agglutinin (PNA), soybean (Glycine max) agglutinin (SBA) and Bauhinia purpurea agglutinin (BPA) showed a strong reaction in the acrosomal region from Golgi to acrosome-phase spermatids in three species of tree shrews. These lectins also showed a granular positive reaction in the cytoplasm from acrosome to maturation-phase spermatids in three species, except that BPA revealed no granular reaction (though it was positive) in the spermatid cytoplasm of the northern smooth-tailed tree shrew and that PNA revealed no reaction in the spermatid cytoplasm of the common tree shrew. While, Griffonia simplicifolia-II agglutinin (GS-II) showed a positive reaction in the acrosomal region of Golgi-phase spermatids in three species of tree shrews. Although GS-II was positive in the spermatocyte cytoplasm of three species, it showed granular in the northern smooth-tailed tree shrew and common tree shrew but not granular in the Java tree shrew. Thus, the lectin-binding patterns in testes were similar among three species belonging to the Order Scandentia. However, slight differences were also detected even among these phylogenetically-close species.

Animals↗

PubMed1977

Complexity of branching dendritic trees: dependence on number of trees per cell and effects of branch loss during sectioning.

We have investigated whether the complexity of dendritic trees is correlated with the number of primary dendrites per neuron (trees per cell). In estimating the average number of branches of centrifugal orders 1-5 per tree we used statistical methods to compensate for loss of parts of trees during sectioning. Limitations of these methods are discussed. Neurons from four populations, stained by the Golgi-Cox method, were examined: stellate cells from layer IV, area 17 of visual cortex, in normal and dark-reared cats; the pyramidal cells from layer V, somatosensory cortex, in two strains of rats. In all four groups of neurons the average number of branches of higher orders (3, 4, 5) per tree tended to be smaller in neurons bearing more trees. Thus all trees from a population of neurons should not be assumed to be equivalent. The decreasin high-order branches per tree tended to offset the increase in number of trees per cell. In three of the four groups these opposed tendencies maintained the average number of high-order branches per neuron nearly independent of the number of trees per cell. Natural selection may have favoured near-constancy in the number of high-order branches to reduce dispersion among neurons of one type in functional input-output rleations.

Animals↗