1. ¹Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002-0948, USA
2. ²Plant Biology Department, University of Georgia, Athens, Georgia 30605, USA
3. ³INRA Station de Recherches Forestieres, Laboratoire de Génétique des Arbres Forestiers BP45 33611 Gazinet Cedex, France
4. ⁴Department of Ecology and Evolution, Herbarium, University of Michigan, Ann Arbor, MI 48109-1048, USA

Correspondence: BD Hardesty, Department of Plant Biology, University of Georgia, 2502 Miller Plant Sciences, Athens, GA 30602, USA. E-mail: hardesty@plantbio.uga.edu

Received 21 December 2004; Accepted 13 June 2005; Published online 10 August 2005.

Abstract

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 dbh10 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.