Mating system variation among populations, individuals and within and among fruits in Bertholletia excelsa

Abstract

The aim of this study was to investigate variation in mating system among three Brazilian Amazon populations of the tree Bertholletia excelsa with different levels of anthropogenic interventions. We collected open-pollinated seeds from one natural population, remnant trees dispersed in a pasture, and trees from a plantation. Outcrossing rate not varied among the populations and indicates that all seeds were originated from outcrossing (tm=1.0). Mating among relatives was significant higher in the plantation than forest and pasture populations, probably due the fact that many trees are related in the plantation. Correlated mating was significantly higher in pasture (rp=0.47) and plantation (rp=0.51) than in the natural population (rp=0.22), suggesting that trees in natural population are pollinated by a higher number of pollen donors. The paternity correlation was significantly higher within (rp(w)=0.41) than among fruits (rp(a)=0.18), showing a higher probability to find full-sibs within than among fruits. The fixation index was generally lower in seed trees than in their seedlings, suggesting selection for heterozygous individuals from seedling to adult stages. Progeny arrays collected from the natural population had a lower proportion of pairwise full-sibs than in pasture and plantation and higher variance effective size (2.75) than trees in pasture (2.15) and plantations (2.22). Results highlight that seed collections for conservation, breeding and reforestation programs preferentially should be carried out in natural populations due low proportion highest variance effective size within progeny.

Research Article Contemporary pollen and seed dispersal in natural populations of Bertholletia excelsa (Bonpl.).

“…Such studies have shown lower genetic differentiation between neighboring natural populations (0.018) than spatially distant populations (0.121), significant SGS (Sujii et al, 2015), and varying levels of inbreeding among populations, with some showing no evidence of inbreeding (Sujii et al, 2015;Wadt et al, 2015). These studies have also demonstrated that reproduction occurs mainly by outcrossing (O'Malley et al, 1988;Wadt et al, 2015), but some mating occurs between related trees. Furthermore, they have found a lower effective number of pollen donors fertilizing seed trees in pastures and plantations than in natural populations, as well as a lower effective number of pollen donors within than among fruits, resulting in higher frequencies of full-sibs in anthropogenic populations and within fruits of trees .…”

“…In MT, the study was carried out in a 75-ha plot (500 x 1500 m, 2.41 trees/ha) established in a mature natural forest, in Dal Pai farm, Itaúba municipality; in AC, the study area was a 375-ha plot (1500 x 2500 m, 0.54 trees/ha) established in a natural forest located in a 420 ha area within the Chico Mendes Extractive Reserve. In both plots, we mapped, measured dbh, and sampled cambium tissue for DNA extraction of all B. excelsa adults (dbh ≥ 50 cm; Wadt et al, 2015) and juvenile trees. In MT, we found 143 adult trees (dbh ranging from 50 to 238 cm, mean ± SD (standard deviation) = 99.1 ± 28.1 cm) and the distance between trees ranged from 16 to 1414 m (mean ± SD = 350 ± 288 m).…”

“…Due to the ecological, social, and economic importance of the species, a series of studies have examined its production (Kainer et al, 2007;Rockwell et al, 2015), demographics (Wadt et al, 2008;Scoles and Gribel, 2012), silviculture (Kainer et al, 2014;Scoles et al, 2016), and genetics (O'Malley et al, 1988;Sujii et al, 2015;Wadt et al, 2015). Some of these studies express concerns about the impact of intensive seed collection on natural regeneration (Wadt et al, 2008;Scoles and Gribel, 2012) and logging on nut production (Rockwell et al, 2015).…”

“…Studies have shown that the crowns of fruiting trees are taller than non-productive trees (Scoles et al, 2016), while silvicultural studies have shown that sapling survival and growth is greatest in full daylight conditions, such as forest gaps (Scoles et al, 2011). Population genetic studies based on genetic markers for B. excelsa have been conducted to better understand its genetic structure and diversity, spatial genetic structure (SGS), and inbreeding and mating systems of natural populations, spatially isolated trees in pastures, and trees in plantations (O'Malley et al, 1988;Sujii et al, 2015;Wadt et al, 2015). Such studies have shown lower genetic differentiation between neighboring natural populations (0.018) than spatially distant populations (0.121), significant SGS (Sujii et al, 2015), and varying levels of inbreeding among populations, with some showing no evidence of inbreeding (Sujii et al, 2015;Wadt et al, 2015).…”

“…Population genetic studies based on genetic markers for B. excelsa have been conducted to better understand its genetic structure and diversity, spatial genetic structure (SGS), and inbreeding and mating systems of natural populations, spatially isolated trees in pastures, and trees in plantations (O'Malley et al, 1988;Sujii et al, 2015;Wadt et al, 2015). Such studies have shown lower genetic differentiation between neighboring natural populations (0.018) than spatially distant populations (0.121), significant SGS (Sujii et al, 2015), and varying levels of inbreeding among populations, with some showing no evidence of inbreeding (Sujii et al, 2015;Wadt et al, 2015). These studies have also demonstrated that reproduction occurs mainly by outcrossing (O'Malley et al, 1988;Wadt et al, 2015), but some mating occurs between related trees.…”