Farruggia, Frank T. .
The buoyancy of Sesbania Scop. (Leguminosae) fruits and the potential contribution of hydrochory to current pantropical distributions.
Phylogenetic evidence reveals two principal subclades within the pantropical legume genus Sesbania Scopoli, one represented by taxa endemic to the New World and the other mainly pantropically distributed taxa. Transoceanic dispersal is a likely explanation for the current pantropical distribution, given the relatively young age estimated for the genus (approximately 18 mya) and the proximity of these taxa to riparian, wetland, and coastal systems. This investigation focuses on the dispersal potential of fruits and seeds through hydrochory. An experiment using both freshwater and seawater treatments was developed to test the buoyancy of pods. The pods represent two geographically and morphologically distinct subgeneric sections of Sesbania. Survival analyses indicate that members of the section Sesbania have lower buoyancy capabilities than section Daubentonia. Seed dormancy was observed to explore the potential for seed germination at loss of buoyancy. The number of seeds that germinated compared to the total number of seeds within each pod that sunk was calculated. The proportion of seeds germinated over time revealed that seed germination in freshwater was highest for all taxa studied. The section Sesbania taxa had earliest germination, with approximately 50% of seeds germinating before the last pod sank. An important adaptation of Sesbania seedlings was observed in the freshwater treatment, when seeds, which had sunk, germinated under water. After expanding their cotyledons, the seedlings became buoyant and developed first and second leaves while floating. The likelihood of trans-Atlantic dispersal via hydrochory for the species sampled from section Sesbania, appears to be lower than that of section Daubentonia taxa sampled. This result is counter to the original hypothesis based on phylogenetic and biogeographic information. The results indicate that potential long-distance dispersal is likely in systems where fruits could be transported for several days or longer, followed by dehiscence and subsequent seedling rafting in freshwater.
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1 - Arizona State University, School of Life Sciences, P.O. Box 874501, Tempe, Arizona, 85287-4501, USA
Presentation Type: Poster:Posters for BSA Sections
Location: Event Tent/Cliff Lodge
Date: Monday, July 27th, 2009
Time: 5:30 PM