Using spatial genetic structure of a population of Swietenia macrophylla King to integrate genetic diversity into management strategies in Southwestern Amazon

Abstract

The aims of this study were to investigate the intrapopulation spatial genetic structure (SGS) of a preserved Swietenia macrophylla population in a managed forest in Southwestern Amazon, in Acre state, Brazil, and assess the genetic parameters that underlie the conceptual framework that guides conservation and management strategies. The study was conducted in Annual Production Unit (APU) 3, where 83 adult trees (DBH ≥ 40 cm) were mapped (1650 ha). The diameter at breast height (DBH) was measured and the vascular exchange was sampled. Leaf tissues were collected from 187 juvenile individuals within a radius of 20 m of adults. The population presented high heterozygosity (H o ) for adult (0.767) and juvenile (0.763) individuals, but significantly high allelic richness (R) and significantly lower fixation index (F ) in adults (R = 10.3, F = 0.048) than juveniles (R = 9.3, F = 0.119). The F value significantly higher for juveniles, suggesting selection against inbred individuals between juvenile and adult life stages. SGS was detected for adults up to 300 m. Mating was mainly through outcrossing (0.97-1.0), but some crossing occurred among related trees (0.02-0.16) and were correlated (r pm = 0.06-0.22), indicating a mean effective number of pollen donors ranging from 4.5 to 18.2. Pollen dispersal distances reached 3905 m (mean of 1472 m), and mean effective pollination neighbor area of 792 ha. The effective population size (N e ) within family (2.73) was lower than expected for random mating populations. The number of trees (m) required for seed collection was estimated at 55 non-inbreed and not related trees to each other. The core collection consisted of 42 (50.6%) adults across the area. These individuals should be included in seed collection as they represent 100% of the total detected genetic diversity. The inclusion of S. macrophylla on the list of species available for exploitation is not indicated, because the species requires cross breeding for its maintenance and logging reduce the N e and may negatively impact the pattern of genetic diversity. These will significantly increase the risk of genetic erosion and population extinction due to a lack of adaptive ability. Adults serve as pollen donors that ecologically and genetically contribute to the maintenance of gene flow and N e . Because it is recognized as a threatened species worldwide, and due to the fact that in areas of natural occurrence the species presents low-density and shows difficulty establishing natural regeneration, we recommend that S. macrophylla be protected from selective logging.

Landscape barriers to pollen and seed flow in the dioecious tropical tree Astronium fraxinifolium in Brazilian savannah

“…The dispersion of seeds over short distances resulted in the strong SGS for A . fraxinifolium in RP due to the increase in average coancestry between pairs of proximal individuals, as also observed by De Oliveira et al [ 62 ]. SGS is mainly supported by the occurrence of genetic drift [ 63 ], caused by the low density of reproductive adults near to RP, which could have resulted in a barrier for the dispersion of pollen and seeds [ 23 ] and high levels of inbreeding due to elevated levels of mating between relatives.…”

“…For regenerant individuals in RP, the fixation index ( F ) indicate a deficiency of heterozygous individuals and, therefore, a reduction in genetic diversity. Biparental inbreeding has been reported in studies of tree species pollinated by animals and insects [ 10 , 16 , 62 , 65 – 67 ]. Here, the observed biparental inbreeding can be due to founder effect [ 68 ] occurring during the colonization process after dam construction, associated to the low density of reproductive individuals along with SGS and the limited pollen dispersal distance in the study.…”

There Is No ‘Rule of Thumb’: Genomic Filter Settings for a Small Plant Population to Obtain Unbiased Gene Flow Estimates

“…With notable reductions in populations, the species has become increasingly rare, with a few remaining small populations. Consequently, both direct measures of dispersal from parentage analyses, as well as indirect estimates of dispersal from fine-scale spatial genetic structure (SGS; i.e., non-random spatial distribution of genotypes within populations), provide useful information for management activities and policies, including seed collection for ex situ conservation, tree breeding, and/or reforestation (e.g., Bittencourt and Sebbenn, 2007 ; Ramos et al, 2018 ; de Oliveira et al, 2020 ).…”

Avaliação técnica e financeira do plantio de enriquecimento em clareiras de exploração com as espécies de alto valor >i<Swietenia macrophylla>/i< king e >i<Handroanthus serratifolius>/i< (Vahl) S.Grose na Amazônia Oriental

“…Swietenia macrophylla King (Meliaceae), conhecida popularmente como Mogno, e Handroanthus serratifolius (Vahl) S.Grose (Bignoniaceae), vulgarmente conhecido como Ipê, Ipê-amarelo ou Pau d'arco, são duas espécies de alto valor econômico por causa da alta qualidade da madeira. As duas espécies são amplamente distribuídas nas florestas tropicais do território brasileiro e ocorrentes principalmente em florestas de terra firme (Schulze et al, 2008b;Andrade et al, 2019;de Oliveira et al, 2020). Swietenia, é uma espécie oportunista, com uma densidade média da madeira de 0,52 -0,80 g/cm³ (Ferraz et al, 2004;IBAMA, 2019).…”

“…Contudo, Swietenia demonstra um elevado nível de diversidade genética e distinção entre as suas populações nos ambientes tropicais em áreas sem manejo (Lemes et al, 2003;Degen et al, 2013). Por isso, críticas têm sido feitas para a EIR por proporcionar a segregação reprodutiva da espécie e o cruzamento não aleatório dos indivíduos, o que fomenta a elevação da homozigose e perda genética na população (de Oliveira et al, 2020). Por ser uma espécie com densidade menor que um indivíduo por hectare e com baixa regeneração natural e taxa de crescimento, a exploração florestal afeta a dispersão dos seus polinizadores e consequentemente a sua reprodução, diminuição de densidade e a manutenção dos remanescentes (Grogan et al, 2014).…”