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We used genotypes from six microsatellite loci and demographic data from a large mapped forest plot to study changes in spatial genetic structure across demographic stages, from seed rain to seedlings, juveniles, and adult diameter classes in the Neotropical tree, Jacaranda copaia. In pairwise comparisons of genetic differentiation among demographic classes, only seedlings were significantly differentiated from the other diameter classes; FST values ranged from 0.006 to 0.009. Furthermore, only seedlings showed homozygote excess suggesting biparental inbreeding in the large diameter reproductive adults. We found very low levels of relatedness in the first distance class of trees, 1–26 cm diameter ( F ij = 0.011). However, there was a 5- to 10-fold rise in relatedness in the smallest distance class, from the smallest to the largest tree diameter classes ( F ij = 0.110 for individuals > 56 cm diameter). A variety of non-mutually exclusive mechanisms have been invoked perviously to explain such a pattern, including natural selection, history, or nonequilibrium population dynamics. The long-term demographic data available for this species allow us to evaluate these mechanisms. Jacaranda is a fast-growing, light-demanding species with low recruitment rates and high mortality rates in the smaller diameter classes. It successfully regenerates only in large light gaps, which occur infrequently and stochastically in space and time. These factors contribute to the nonequilibrium population dynamics and observed low genetic structure in the small size classes. We conclude that the pattern of spatial genetic transitions in Jacaranda is consistent with overlapping related generations and strong but infrequent periods of high recruitment, followed by long periods of population decline. [ABSTRACT FROM AUTHOR]

Summary 1 Primate frugivores are important seed dispersers for a large fraction of tree species in many tropical forests. The movement, diet preferences and defecation patterns produced by primates may therefore strongly influence seed dispersion patterns and seedling recruitment success. Here we examine the pattern of seed dispersal generated by white-faced monkeys (Cebus capucinus ) in relation to adult tree distribution in the 50-ha plot on Barro Colorado Island (BCI), Panamá. 2 Diet breadth of Cebus was remarkably wide. Over four months they consumed fruits of 95 out of an estimated 240 species available. Seeds of 67 species passed intact through the gut and 28 were spat out. 3 Dispersal effectiveness of Cebus was also high. Two Cebus groups on average spent < 10 min feeding in individual trees, had large home ranges (> 150 ha), travelled 1–3 km day-1 and defecated seeds in small clumps throughout the day. 4 Mean dispersal distance of ingested seeds was 216 m (range 20–844 m), with the highest probability of dispersal 100–200 m from the parent plant. For six of nine species studied, the distance between defecation sites and nearest conspecific adults of seeds in faeces was not significantly different from random expectations. 5 The scattered dispersal pattern produced by Cebus suggests that this species contributes relatively little to dispersal limitation (sensu Nathan & Muller-Landau 2000) compared to other dispersers in the community. Long-distance dispersal by Cebus resulted in substantial movement of seeds in and out of the 50 ha plot, and suggests that inverse modelling procedures to estimate dispersal functions from trap data may not adequately describe dispersal patterns generated by this primate. [ABSTRACT FROM AUTHOR]

Summary 1 We examined how seed size and seedling growth rate influence recruitment success of neotropical pioneer species. We investigated the soil seed bank, and followed seedlings from emergence and establishment to the sapling stage in artificially created gaps in secondary forest on the Barro Colorado Nature Monument, Panamá. 2 To simulate microsite variation within gaps, litter addition/removal and soil disturbance treatments were applied to seedling plots in a factorial design. 3 Seedling emergence was almost three-fold higher in litter-free plots than in control plots. 4 We found a negative relationship between seed mass and seed abundance in the soil, seed mass was positively correlated with seedling emergence success from the seed bank and with seedling survival through to the end of the first dry season. 5 In the 18 months following the first dry season we observed an uncoupling of seed mass from seedling performance. Seedling mortality was now a function of maximum relative growth rate, with higher mortality of fast-growing species attributable to herbivory, notably by shoot-borers. 6 We propose that a seed size-dependent trade-off between dispersal success (selecting for large seed number), and emergence–establishment success (selecting for large seed size) can explain the maintenance of wide variation in seed size among pioneer species. Secondarily, a trade-off between growth rate and susceptibility to herbivores acting at the post-establishment phase may contribute to observed differences in light requirements among pioneer species. [ABSTRACT FROM AUTHOR]

1. One proposed mechanism by which tree species coexist is through partitioning gradients of light availability. We performed a pot experiment in which seedlings of 12 pioneer species were established in 30% light, then transplanted to six light treatments designed to simulate natural gaps ranging from 25 m2 (≈10% full sun) to 800 m2 (60% full sun). Plants were harvested after 56–117 days, and comparisons were made of allocation patterns and growth and carbon assimilation rates.2. Species varied strongly in their maximum relative growth rate (RGR, range 15·4–83·6 mg g−1 day−1). However, we found little evidence for gap-size partitioning based on growth rate, as species RGR in large and small simulated gaps was strongly correlated (r = 0·83,P < 0·001).3. Species differences in growth reflected variation in both physiology and allocation. Net assimilation rate was a strong determinant of RGR across all simulated gap sizes (r2 = 0·60–0·71,P < 0·001). Leaf area ratio was a poor predictor of growth rate under all gap sizes (r2 = 0·04–0·08, NS).4. The maximum rate of net C assimilation (Amax) increased significantly with simulated gap size for all but one pioneer species, but only when measured on a per area basis. Among species variation inAmax was only weakly related to RGR. Foliar nitrogen concentration varied widely among species (range 2·2–4·7% dry mass), but was only weakly correlated with RGR (r2 = 0·04–0·30).5. Previous growth analyses of tropical seedlings have identified both specific leaf area (SLA) and seed mass as key traits correlated with growth rate. Although SLA varied twofold and seed mass more than a thousand-fold among the pioneer species in this study, neither trait was significantly correlated with among-species variation in RGR. Although these traits underlie major differences in life history between shade-tolerant and pioneer species, they contribute little to variation in growth performance within the pioneer functional group.Functional Ecology(2004)18, 725–736 [ABSTRACT FROM AUTHOR]

Tropical tree size distributions are remarkably consistent despite differences in the environments that support them. With data analysis and theory, we found a simple and biologically intuitive hypothesis to explain this property, which is the foundation of forest dynamics modeling and carbon storage estimates. After a disturbance, new individuals in the forest gap grow quickly in full sun until they begin to overtop one another. The two-dimensional space-filling of the growing crowns of the tallest individuals relegates a group of losing, slow-growing individuals to the understory. Those left in the understory follow a power-law size distribution, the scaling of which depends on only the crown area--to--diameter allometry exponent: a well-conserved value across tropical forests. [ABSTRACT FROM AUTHOR]

Species coexistence in diverse communities likely results from multiple interacting factors. Mechanisms such as conspecific negative density dependence (CNDD) and varying life-history strategies related to resource partitioning are known to influence plant fitness, and thereby community composition and diversity. However, we have little understanding of how these mechanisms interact and how they vary across life stages. Here, we document the interaction between CNDD and lifehistory strategy, based on growth-mortality trade-offs, from seedling to adult tree for 47 species in a tropical forest. Species' life-history strategies remained consistent across stages: fast-growing species had higher mortality than slow-growing species at all stages. In contrast, mean CNDD was strongest at early life stages (i.e. seedling, sapling). Fast-growing species tended to suffer greater CNDD than slow-growing species at several, but not all life stages. Overall, our results demonstrate that coexistence mechanisms interact across multiple life stages to shape diverse tree communities. [ABSTRACT FROM AUTHOR]

Sjögren's syndrome ( SS) is an autoimmune inflammatory disease that primarily affects the lacrimal and salivary glands causing dry eyes and mouth. Antibodies to Ro60 are observed frequently in patients with SS; however, the role of these antibodies in SS initiation and progression remains unclear. The sequence Ro60 273-289 ( Ro274) is a known B cell epitope of Ro60 and antibodies to this epitope have been observed in a subset of SS patients and in animals immunized with Ro60 protein. Animals immunized with Ro274 linear peptide develop a Sjögren's-like illness. We hypothesized that passive transfer of anti- Ro274-specific immunoglobulin ( Ig)G would induce a Sjögren's-like phenotype. To evaluate this hypothesis, we adoptively transferred affinity-purified Ro274 antibodies into naive BALB/c animals, then evaluated salivary gland histology, function and IgG localization 4 days post-transfer. At this time-point, there was no demonstrable mononuclear cell infiltration and salivary glands were histologically normal, but we observed a functional deficit in stimulated salivary flow of animals receiving Ro274 antibodies compared to animals receiving control IgG. Cellular fractionation and enzyme-linked immunosorbent assay revealed Ro274-specific antibodies in the nucleus and cytoplasmic fractions of isolated parotid salivary gland cells that was confirmed by immunohistochemistry. These data support the hypothesis that antibodies to Ro274 deposit in salivary glands can enter intact salivary gland cells and are involved in the dysregulation of salivary flow in SS. [ABSTRACT FROM AUTHOR]

Seed dispersal is a critical but poorly understood life-history stage of plants. Here we use a genetic approach to describe seed dispersal patterns accurately in a natural population of the Neotropical tree species Jacaranda copaia (Bignoniaceae). We used microsatellite genotypes from maternally derived tissue on the diaspore to identify which individual of all possible adult trees in the population was the true source of a given seed collected after it dispersed. Wind-dispersed seeds were captured in two different years in a large array of seed traps in an 84-ha mapped area of tropical forest on Barro Colorado Island, Panama. We were particularly interested in the proportion of seeds that traveled long distances and whether there was evidence for direct dispersal into gaps, which are required for successful recruitment of this pioneer tree species. Maximum likelihood procedures were used to fit single- and multiple-component dispersal kernels to the distance data. Mixture models, with separate distributions near and far, best fit the observed dispersal distances, albeit with considerable uncertainty in the tail. We discuss the results in light of different mechanisms responsible for separate distributions near the adult source and in the tail of the curve. [ABSTRACT FROM AUTHOR]

Simarouba amara (Simaroubaceae) is a vertebrate-dispersed, insect-pollinated Neotropical tree found in lowland moist forest from upper Mesoamerica to the Amazon basin. We assessed the spatial genetic structure of S. amara within the 50-ha Forest Dynamics Plot on Barro Colorado Island in the Republic of Panama. A total of 300 individuals were genotyped using five microsatellite loci, representing 100 individuals with a dbh10 cm, 100 individuals of 1–10 cm dbh, and 100 individuals of <1 cm dbh. The 200 individuals in the two larger size classes were also genotyped with 155 AFLP loci. Spatial autocorrelation analysis using Moran's Index detected significant genotypic association at the smallest distance classes for 1–10 cm dbh (0–20 m) and >10 cm dbh (0–40 m) size categories. Significant spatial autocorrelations were detected over larger scales (0–140 m) in <1 cm dbh individuals. The relatively weak genetic structure of S. amara, in comparison to other recent studies, may be explained by pollen and seed dispersal over the 50 ha plot, overlapping seed shadows, and postrecruitment mortality.Heredity (2005) 95, 290–297. doi:10.1038/sj.hdy.6800714; published online 10 August 2005 [ABSTRACT FROM AUTHOR]

We isolated eight polymorphic microsatellites from the neotropical tree Luehea seemannii for gene flow and genetic structure studies. We used a streptavidin subtractive enrichment technique to develop a library of CA/GT repeats. Eight loci were screened for diversity from 96 individuals from Barro Colorado Island (BCI) and neighbouring Gigante peninsula in Panama. Luehea seemannii shows moderate levels of genetic diversity within these two populations. Allelic richness ranged from four to nine alleles and averaged 6.44 alleles per locus. Average expected heterozygosity was 0.65 on BCI and 0.60 on Gigante. Results are compared to microsatellite data from another wind-dispersed gap colonizing species common in Panama. [ABSTRACT FROM AUTHOR]

Summary 1 We examined the importance of seed dispersal in predicting the pioneer seedling composition in recent gaps in a forest plot on Barro Colorado Island (BCI), Panama. We characterize seed dispersal for 13 taxa from seed rain data collected over 13 years in 200 mesh traps, and for an additional species from germination from soil samples collected in one year. We describe seedling distribution patterns from a complete census of all seedlings of these 14 taxa present in 36 treefall gaps. 2 A maximum likelihood model, incorporating both distance to adult trees and tree size, fitted observed seed rain to traps quite well for all taxa. 3 The ability to predict seedling recruit number per gap varied greatly among taxa. For 8 of 14 taxa, regression models incorporating predicted seed rain were significantly better predictors of seedling recruitment than models in which recruitment probability was assumed constant in all sites. 4 To see if variation in local dispersal patterns determined the community composition of gaps, we examined the relative abundances of these 14 pioneer taxa in the 36 gaps. We found that taxon abundances were significantly positively correlated with abundances predicted from seed dispersal models and seed–seedling regressions for 27 out of 36 gaps. 5 Overall, we find evidence that limited seed dispersal is an important factor contributing, together with factors affecting post-dispersal recruitment success, to seedling distribution patterns in gaps. [ABSTRACT FROM AUTHOR]

Tropical tree communities are shaped by local-scale habitat heterogeneity in the form of topographic and edaphic variation, but the life-history stage at which habitat associations develop remains poorly understood. This is due, in part, to the fact that previous studies have not accounted for the widely disparate sample sizes (number of stems) that result when trees are divided into size classes. We demonstrate that the observed habitat structuring of a community is directly related to the number of individuals in the community. We then compare the relative importance of habitat heterogeneity to tree community structure for saplings, juveniles and adult trees within seven large (24-50 ha) tropical forest dynamics plots while controlling for sample size. Changes in habitat structuring through tree life stages were small and inconsistent among life stages and study sites. Where found, these differences were an order of magnitude smaller than the findings of previous studies that did not control for sample size. Moreover, community structure and composition were very similar among tree sub-communities of different life stages. We conclude that the structure of these tropical tree communities is established by the time trees are large enough to be included in the census (1 cm diameter at breast height), which indicates that habitat filtering occurs during earlier life stages. [ABSTRACT FROM AUTHOR]