Rapid access to genetic information is central to the revolution taking place in molecular genetics. The simultaneous analysis of the entire human mitochondrial genome is described here. DNA arrays ...containing up to 135,000 probes complementary to the 16.6-kilobase human mitochondrial genome were generated by light-directed chemical synthesis. A two-color labeling scheme was developed that allows simultaneous comparison of a polymorphic target to a reference DNA or RNA. Complete hybridization patterns were revealed in a matter of minutes. Sequence polymorphisms were detected with single-base resolution and unprecedented efficiency. The methods described are generic and can be used to address a variety of questions in molecular genetics including gene expression, genetic linkage, and genetic variability.
The importance of dispersal for the maintenance of biodiversity, while long-recognized, has remained unresolved. We used molecular markers to measure effective dispersal in a natural population of ...the vertebrate-dispersed Neotropical tree, Simarouba amara (Simaroubaceae) by comparing the distances between maternal parents and their offspring and comparing gene movement via seed and pollen in the 50 ha plot of the Barro Colorado Island forest, Central Panama. In all cases (parent-pair, mother-offspring, father-offspring, sib-sib) distances between related pairs were significantly greater than distances to nearest possible neighbours within each category. Long-distance seedling establishment was frequent: 74% of assigned seedlings established > 100 m from the maternal parent mean = 392 ± 234.6 m (SD), range = 9.3-1000.5 m and pollen-mediated gene flow was comparable to that of seed mean = 345.0 ± 157.7 m (SD), range 57.6-739.7 m. For S. amara we found approximately a 10-fold difference between distances estimated by inverse modelling and mean seedling recruitment distances (39 m vs. 392 m). Our findings have important implications for future studies in forest demography and regeneration, with most seedlings establishing at distances far exceeding those demonstrated by negative density-dependent effects.
According to the Janzen-Connell hypothesis for the maintenance of species diversity, recruitment is inhibited in the immediate vicinity of adults by herbivores and pathogens. This reduces the per ...capita ability of abundant species to reproduce, relative to less common species, and gives rare or competitively inferior species a greater chance to persist. We tested this hypothesis in a 50-ha mapped plot of tropical moist forest on Barro Colorado Island, Panama, by investigating the spatial patterns of sapling recruitment in 80 species of trees and shrubs. Two censuses of adults and saplings were carried out, in 1982 and in 1985. Recruits were defined as saplings of 1-8 cm dbh (diameter breast height) appearing in the 1985 census that were not present in 1982. The distance from each recruit to its nearest conspecific adult neighbor was measured. At various distances from adults, the number of conspecific recruits and the number of recruits of all species were tallied. The ratio of recruits of species i to all recruits was taken as an estimate of the probability that species i would occupy that site as an adult. A few species showed a significant reduction in recruitment probability close to adults, but more species showed a significant increase, and many other species showed no significant spatial pattern. Among canopy trees, about a third of the species showed some sign of local reduction in recruitment, but the distance over which the effect extended was usually less than 5 m; however, the most abundant canopy tree, Trichilia tuberculata, showed a sharp reduction in recruitment probability up to 10 m from adults. In treelets and shrubs, most species showed strong peaks in recruitment probability close to adults. Thus, most recruitment patterns did not fit the prediction of Janzen and Connell; however, two to three of the most common species may have reached densities at which a depression in local recruitment is regulating abundance.
Diameter, height, crown shape and crown area were measured on 23-42 trees ranging in size from saplings to large adults for each of eight common dicotyledonous tree species in a neotropical forest on ...Barro Colorado Island, Panama.
We have recently reported the attachment and spreading of human umbilical vein endothelial cells (HUVECs) upon substrates
containing covalently grafted Arg-Glu-Asp-Val (REDV) peptide (Hubbell, J. A., ...Massia, S. P., Desai, N. P., and Drumheller,
P. D. (1991) Bio/Technology 9, 568-572). This peptide has been reported to be the minimal active sequence within the CS5 site
of the alternatively spliced type III connecting segment (IIICS) region of fibronectin, and the integrin alpha 4 beta 1 has
been identified as the receptor on melanoma cells for this site. The integrin alpha 4 beta 1 has also been identified as the
receptor for the CS1 site in the IIICS region on cells of neural crest origin, melanoma cells, lymphocytes, and hematopoietic
stem cells. In this study, we demonstrate that this integrin also serves as a receptor on HUVECs for the peptide REDV from
the CS5 site. The alpha 4 subunit was shown to be expressed upon HUVEC membranes by whole-cell enzyme-linked immunosorbent
assay. Antifunctional antibodies directed against integrin subunits alpha 4 and beta 1 inhibited cell adhesion on REDV-grafted
substrates, but not on RGD-grafted substrates. The alpha 4 subunit localized into fibrillar structures within spread cells
on the REDV-grafted substrates, but not within spread cells on RGD-grafted substrates. Two proteins (144 and 120 kDa) were
isolated from HUVEC extracts by REDV ligand affinity chromatography and were demonstrated by immunoprecipitation and Western
blot to be the integrin subunits alpha 4 (144 kDa) and beta 1 (120 kDa); furthermore, the immunoprecipitation analyses demonstrated
that the subunits formed a complex. HUVEC binding to REDV-grafted substrates was inhibited by both soluble REDV and RGD, demonstrating
that adhesion was biospecific and that the REDV peptide is RGD-like. In this report we demonstrate for the first time that
alpha 4 is present in the endothelial cell membrane, in contrast to previous reports by others, and that integrin alpha 4
beta 1 is the receptor for REDV-mediated adhesion to the IIICS region of region of plasma fibronectin.
In large samples of trees ≥1 cm dbh (more than 1 million trees and 3000 species), in six lowland tropical forests on three continents, we assigned species with >30 individuals to one of six classes ...of stature at maturity (SAM). We then compared the proportional representation of understory trees (1-2 cm dbh) among these classes. The understory of the three Asian sites was predominantly composed of the saplings of large-canopy trees whereas the African and American sites were more richly stocked with trees of the smaller SAM classes. Differences in class representation were related to taxonomic families that were present exclusively in one continent or another. Families found in the Asian plots but not in the American plot (e.g., Dipterocarpaceae, Fagaceae) were predominantly species of the largest SAM classes, whereas families exclusive to the American plots (e.g., Melastomataceae sensu stricto, Piperaceae, and Malvaceae Bombacacoidea) were predominantly species of small classes. The African plot was similar to Asia in the absence of those American families rich in understory species, while similar to America in lacking the Asian families rich in canopy species. The numerous understory species of Africa were chiefly derived from families shared with Asia and/or America. The ratio of saplings (1-2 cm dbh) to conspecific canopy trees (>40 cm dbh) was lower in American plots than in the Asian plots. Possible explanations for these differences include phenology, moisture and soil fertility regimes, phyletic constraints, and the role of early successional plants in forest development. These results demonstrate that tropical forests that appear similar in tree number, basal area, and the family taxonomy of canopy trees nonetheless differ in ecological structure in ways that may impact the ecology of pollinators, dispersers, and herbivores and might reflect fundamental differences in canopy tree regeneration.
Gap-edge trees were significantly more likely to fall into pre-existing gaps than in other directions in a moist tropical forest on Barro Colorado Island (BCI), Panama. Trees not at gap edges were ...more likely to fall away from near neighbors than toward them. We show that gross asymmetries of tree crowns were the rule rather than the exception for all trees. The crowns of most gap-edge trees were strongly asymmetrical into their adjoining gaps, and trees not at gap edges were strongly asymmetrical way from near neighbors. Trees had a strong and significant tendency to fall on these heavy sides. Such treefalls, and related limbfalls, can result in redistribution of gaps and a retardation of gap regeneration. An analysis of 5 yr of canopy height data from a mapped 50-ha plot on BCI revealed that sites within larger gaps were significantly more likely to be redisturbed by secondary treefalls than were sites in the smallest gaps or nongap quadrats. These results suggest that treefall gaps in tropical forest may be more persistent disturbances than previously thought.
Azoxystrobin is applied early in the sugar beet growing season in north-central United States for control of Rhizoctonia damping-off and Rhizoctonia crown and root rot caused by Rhizoctonia solani ...anastomoses groups (AGs) 4 and 2-2, respectively. Fungicide application timings based on crop growth stage and soil temperature thresholds were evaluated in inoculated small-scale trials and in commercial fields with a history of Rhizoctonia crown and root rot. Soil temperature thresholds of 10, 15, and 20°C were selected for fungicide application timings and used to test whether soil temperature could be used to better time applications of azoxystrobin. In both small- and large-plot trials, timing applications after attainment of specific soil temperature thresholds did not improve efficacy of azoxystrobin in controlling damping-off or Rhizoctonia crown and root rot compared with application timings based on either planting date, seedling development, or leaf stage in a susceptible (E-17) and a resistant (RH-5) cultivar. Application rate and split application timings of azoxystrobin had no significant effect on severity of crown and root rot. Other environmental factors such as soil moisture may interact with soil temperature to influence disease development. Cv. RH-5 had higher sugar yield attributes than the susceptible cultivar (E-17) in seasons conducive and nonconducive to crown and root rot development. All isolates recovered from both small- and large-plot trials in all years were AG 2-2. R. solani AG 4 was not identified in any samples from any year.
Comparison of the spatial distribution of stem cankers on the canopy tree Ocotea whitei (Lauraceae) in a 20-ha plot on Barro Colorado Island, Panama, with spatial and temporal patterns of mortality ...in this host over the previous decade. The cankers occur both on adult and juvenile individuals, although juveniles are much more likely to show symptoms than adults. Disease incidence is host-density dependent, and both the presence of the disease and host mortality are more likely close to than far from a conspecific adult, which resulted in a net spatial shift of the juvenile population away from conspecific adults through time. Disease incidence is lower than expected among juveniles of O. whitei growing near to adults of the non-susceptible canopy tree Beilschmiedia pendula. The coincidence of spatial patterns of canker incidence and host mortality suggest a role for the disease in regulating host spatial distribution, in agreement with predictions of the Janzen-Connell hypothesis.
Predicting Species Diversity in Tropical Forests Plotkin, Joshua B.; Potts, Matthew D.; Yu, Douglas W. ...
Proceedings of the National Academy of Sciences - PNAS,
09/2000, Letnik:
97, Številka:
20
Journal Article
Recenzirano
Odprti dostop
A fundamental question in ecology is how many species occur within a given area. Despite the complexity and diversity of different ecosystems, there exists a surprisingly simple, approximate answer: ...the number of species is proportional to the size of the area raised to some exponent. The exponent often turns out to be roughly 1/4. This power law can be derived from assumptions about the relative abundances of species or from notions of self-similarity. Here we analyze the largest existing data set of location-mapped species: over one million, individually identified trees from five tropical forests on three continents. Although the power law is a reasonable, zeroth-order approximation of our data, we find consistent deviations from it on all spatial scales. Furthermore, tropical forests are not self-similar at areas ≤ 50 hectares. We develop an extended model of the species-area relationship, which enables us to predict large-scale species diversity from small-scale data samples more accurately than any other available method.
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