Abstract
The quantification of genetic diversity and intrapopulation spatial genetic structure (SGS) of tree species are important aspects for in and ex situ conservation practices. In this study we seek to understand the importance of conservation areas by quantifying the genetic diversity and the spatial genetic structure of a natural population of Theobroma speciosum. Within this population, 49 adults and 51 subadults were genotyped for five microsatellite loci. The results showed that adults and subadults have similar levels of genetic diversity and inbreeding (adults: A= 10.4, Ae = 10.3, F= 0.68, subadults: A= 10.6, Ae= 10.6, F= 0.57). Genetic diversity was spatially structured within the population, and the results suggest that near-neighbor trees up to a distance of 70 m are likely related. SGS is likely the result of short-distance seed dispersal, the short-distance range of pollinators, and infrequent breaches of the self-incompatible mating system. Considering the high demographic density of the species and size of the study area, as well as the high average number of alleles per locus and the presence of rare alleles, we believe that the study population is an excellent resource for in situ genetic conservation of T. speciosum. The study area is also a useful resource for collecting germplasm for ex situ conservation and seed collection, either for breeding programs used in the restoration of degraded areas or forest improvement.
Highlights
Genetic diversity in adults and subadults: The T. speciosum population presented a high level of genetic diversity for the loci analyzed in this study
The number of alleles per locus and the mean effective number of alleles per locus were consistent with the results reported by Nybom (2004) who reviewed 106 studies of intraspecific genetic diversity in natural tree species using microsatellite markers, and found a mean of 9.9 alleles per locus
According to Alves et al (2007), most tropical tree species present a large number of alleles per locus and, a high level of expected heterozygosity
Summary
This species is important because it represents a possible source of genetic resistance for other, more economically important species, such as Theobroma cacao (Silva et al, 2011). While some natural populations of Theobroma species are protected in conservation units, such as the Juruena Nation Park, other populations face increasing pressure from forest fragmentation and exploitation. Our aim was to determine the importance of conservation units, like the Juruena National Park, in protecting the genetic diversity of tree species of this area. We assess the genetic diversity and the spatial genetic structure (SGS) of a natural population of T. speciosum in Juruena National Park, as well as to provide a census of adults and subadults of T. speciosum in the population. We addressed the following questions: (i) Are there differences in the levels of genetic diversity between adult and subadult populations? (ii) Is genetic diversity spatially structured within the population? (iii) What is the minimum distance required between seed trees to collect seeds for conservation programs?
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