Mahogany, Swietenia macrophylla (Meliaceae) is the most valuable
hardwood species in Neotropics and is seriously threatened owing to
over-exploitation and habitat destruction. The population genetic
structure and mating system of S. macrophylla were studied in the
Brazilian Amazon for conservation purposes. Ten highly polymorphic
micro satellite markers were developed from an enriched genomic library
of S. macrophylla and combined in three multiplexed fluorescence based
genotyping systems. The number of alleles per locus ranged from
11 to 25 (mean = 15.8). The probability of genetic identity (7x10- 15) and
the probability of paternity exclusion (0.999998) found over all loci
indicate the high discriminating power of these markers.
The genetic structure was investigated in seven populations 8-
2,103 km apart. High genetic diversity was detected within populations
(mean He = 0.761, range 0.719-0.800) and a significant level of
inbreeding was found (f = 0.046, P<0.0001, range 0.014-0.097)
indicating nonrandom mating of individuals within populations. Genetic
differentiation among populations was significant (A = 0.12 and p =
0.14, P<0.0001), but no clear pattern of isolation by distance was
found. Conservation strategies for mahogany should take into account
the existence of important genetic structuring of populations.
S. macrophylla seems to have adaptations that preferentially
produce outcrossed progeny but also allows for selfing. The high multilocus outcrossing rate (tm = 0.958) estimated for one population
indicated that, although there was a prevalence of outcrossing, selfing
was not negligible. Around 4-6% of seedlings in the population were
likely to have resulted from self-fertilization and substantial biparental
inbreeding was denoted by the significant difference between the
multilocus and singlelocus estimates (tm - ts = 0.14). Owing to the
species pre-adaptation to colonize newly open, disturbed habitats, many
of the remaining trees in logged areas may persist as viable individuals
which could be very important for population recovery and genetic
conservation programmes