Genetic evidence of frequent long-distance recruitment in a vertebrate-dispersed tree

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

Geographic influence on genetic structure in the widespread Neotropical tree, Simarouba amara (Simaroubaceae)

This study aimed to assess the population genetic structure of a widespread Neotropical tree species, Simarouba amara, at local, regional and continental spatial scales. We used five microsatellite loci to examine genetic variation in 14 natural populations (N=478 individuals) of this vertebrate dispersed rain forest tree species in Panama, Ecuador, and French Guiana. Estimates of genetic differentiation (Fst and Rst) were significant among all but one population pair and global differentiation was moderate (Fst=0.25, Rst=0.33) with 94% of genetic variation ascribed to differences among three main geographic regions (Central America, Western Ecuador, Amazon basin). There was no evidence of isolation by distance within regions. Allele-size mutations contributed significantly (RST > FST) to the divergences between cis and trans-Andean populations, highlighting the role of the northern Andean cordilleras as an important geographic barrier for this species.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83290/1/Hardesty2010TrPB.pd

Spatial genetic structure of Simarouba amara Aubl. (Simaroubaceae), a dioecious, animal-dispersed Neotropical tree, on Barro Colorado Island, Panama

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 dbhX10 cm, 100 individuals of 1–10cmdbh, and 100 individuals of o1 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 410 cm dbh (0–40 m) size categories. Significant spatial autocorrelations were detected over larger scales (0–140 m) in o1 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 post recruitment mortality.http://deepblue.lib.umich.edu/bitstream/2027.42/83301/1/Hardesty2005.pd