Genetic variation in Costa Rican populations of Spanish Cedar
A.C.M, Gillies, J.P. Cornelius, A.C. Newton, C. Navarro, M. Hernandez and J. Wilson.
1997.
Molecular Ecology 6:1133-1145.
Institute of Terrestrial Ecology (ITE), Centro Agronomico Tropical de Investigacion y
Ensenanza (CATIE)
© Photo courtesy of C. Navarro.
INTRODUCTION
Spanish Cedar, Cedrela odorata, an economically important timber species native to the
American tropics, is the focus of increasing conservation concern due to high rates of
deforestation within its native range. To assess the extent of the genetic diversity
within and between populations of the species, samples from 10 widely dispersed
populations within Costa Rica were analysed for random amplified polymorphic DNA (RAPD)
variation.
METHODS
Fourteen decamer primers were used to generate 97 polymorphic RAPD bands. Presence/absence
data for all bands were subjected to a pairwise genetic distance analysis according to
Jaccard’s coefficient. A neighbour-joining dendrogram was constructed from these
distances and an analysis of molecular variance (AMOVA) was used to assess levels of
differentiation between populations and regions. In addition, Shannon’s Diversity
Index was used to quantify levels of diversity within and between populations.
RESULTS
Results indicated highly significant genetic differentiation (P < 0.004, AMOVA) between
populations originating from North Pacific and Atlantic/South Pacific ecotypic regions of
Costa Rica, where 35.3% of the total variation was attributable to molecular differences
between these areas.
Estimated values for within-population diversity were found to vary greatly for the
different RAPD primers. However overall most diversity was present within populations.
(AMOVA variance component 65.1%) which expected for a highly outcrossing tropical tree
species.
IMPLICATIONS
1. North Pacific and Atlantic/South Pacific populations of C. odorata were found to be
significantly different using DNA fingerprinting techniques. To maintain genetic variation
within the species, these two ecotypes should be recognised separately for conservation
strategies.
2. Germplasm conservation and collection must take account of the breadth of genetic
variation present within the species and within populations.
3. In the event of cultivation becoming established in areas where C. odorata is rare,
seed from the same ecotypic zone should be used to prevent genetic pollution.
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