Pollen and seed dispersal of Brazil nut trees in the southwestern Brazilian Amazon

Abstract

Pollen and seed dispersal patterns greatly influence the spatial distribution of plant genetic diversity. Microsatellite-based parentage analysis provides accurate estimates of contemporary gene dispersal. Although most tropical trees have been shown to exhibit widespread pollen dispersal, few studies have estimated contemporary gene dispersal after seedling establishment. Bertholletia excelsa (Lecythidaceae) is pollinated by large-bodied bees, while previous seed-tracking experiments suggest their seeds are mainly dispersed across very short distances by scatter-hoarding rodents, who primarily act as seed predators. Here we used parentage analysis to provide contemporary estimates of pollen and seed dispersal in B. excelsa recruits. We examined six 25-ha plots located in two natural stands in the Acre River valley, in the southwestern Brazilian Amazon. We used 11 microsatellite markers to estimate genetic diversity and fixation index parameters in adults, seedlings and saplings. Genetic diversity was moderate and did not differ across size classes or sampling locations. We assigned pollen and seed parents for < 20% of the recruits, indicating that most events of realized gene flow occurred beyond our 25-ha plots. Only 10 parentage assignments were confirmed with 80% confidence. Pollen distance ranged from 33 to 372 m and seed dispersal from 58 to 655 m. Actual seed-dispersal distances were far greater than the estimates obtained in previous seed-tracking experiments. Thus, studies encompassing larger sampling areas are necessary to determine a more representative spatial scale of B. excelsa’s pollen and seed dispersal capacity in natural stands.

Genetic threats to the Forest Giants of the Amazon: Habitat degradation effects on the socio‐economically important Brazil nut tree (Bertholletia excelsa)

“…Based on molecular markers, Martins et al. (2018) assigned pollination distances in between 33 and 372m, although parentage was assigned to only less than 20% of their studied progeny, suggesting that most realized gene flow occurred beyond their 25‐ha plots. Seed dispersal is restricted to several dozens to few hundreds of meters.…”

“…These interactions are crucial to the extent of gene flow of this species: Bumble bees can fly over several dozens of kilometers, although pollinating mating distances can range from neighboring to distantly located adult trees. Based on molecular markers, Martins et al (2018) assigned pollination distances in between 33 and 372m, although parentage was assigned to only less than 20% of their studied progeny, suggesting that most realized gene flow occurred beyond their 25-ha plots. Seed dispersal is restricted to several dozens to few hundreds of meters.…”

“…Seed dispersal is restricted to several dozens to few hundreds of meters. In the same study and parentage analyses, Martins et al (2018) estimated seed dispersal from assigned mother trees to range from 58 to 655 m for significant assignments obtained within their 25ha plots. These results were based on a relaxed 80% threshold for parentage analyses, and contrast with previous results using traditional methods, with much more restricted dispersal rates of rarely more than 25m away from adult trees (Haugaasen et al, 2010).…”

Climate change drives spatial mismatch and threatens the biotic interactions of the Brazil nut

“…Pollination by bees is essential for fruit production because the presence of pollinators increases crop amount and genetic diversity. The loss of pollinators, therefore, affects long-term viability of populations of the Brazil nut tree (Baldoni et al, 2017;Cavalcante et al, 2012;Martins et al, 2018).…”

Padrão espacial da castanheira em florestas no sul do Amapá, Amazônia Oriental

“…O fruto da B. excelsa é um produto florestal nãomadeireiro de ampla aceitação no mercado nacional e internacional. A exportação há mais de um século, constituindo-se na colheita de sementes feita exclusivamente em florestas tropicais primárias (MARTINS et al, 2018). No entanto, sem a preservação deste importante produto extrativista amazônico, poderá levar esta atividade a um declínio (SANTANA et al, 2018).…”