Rivers shape population genetic structure in Mauritia flexuosa (Arecaceae)

Abstract

The Mauritia flexuosa L.f. palm is known as the “tree of life” given its importance as fundamental food and construction resources for humans. The species is broadly distributed in wet habitats of Amazonia and dry habitats of the Amazon and Orinoco river basins and in the Cerrado savanna. We collected 179 individuals from eight different localities throughout these habitats and used microsatellites to characterize their population structure and patterns of gene flow. Overall, we found high genetic variation, except in one savanna locality. Gene flow between populations is largely congruent with river basins and the direction of water flow within and among them, suggesting their importance for seed dispersal. Further, rivers have had a higher frequency of human settlements than forested sites, contributing to population diversity and structure through increased human use and consumption of M. flexuosa along rivers. Gene flow patterns revealed that migrants are sourced primarily from within the same river basin, such as those from Madeira and Tapajós basins. Our work suggests that rivers and their inhabitants are a critical element of the landscape in Amazonia and have impacted the dispersal and subsequent distribution of tropical palm species, as shown by the patterns of genetic variation in M. flexuosa.

High genetic diversity with low connectivity among Mauritia flexuosa (Arecaceae) stands from Ecuadorean Amazonia

“…Theoretically, a reduction in genetic diversity is expected for small, highly fragmented populations (Lowe et al., 2009). However, our results are similar to those observed from eight populations of Mauritia flexuosa scattered throughout the Brazilian Amazon ( N A = 4.6–7; H E = 0.63–0.74; Sander et al., 2018) and from 46 Mauritia flexuosa populations distributed throughout its biogeographical range ( N A = 4.4–11.8; H E = 0.52–0.88; Melo et al., 2018); both studies also based on microsatellites loci. The high diversity detected among the Mauritia flexuosa stands could be partially explained by ongoing gene flow, which although is low ( N m =0.29), maintains a certain level of diversity (Lowe & Allendorf, 2010).…”

“…These values suggest a mating among full‐sibs and support the occurrence of intrapopulation spatial genetic structure which leads to a reduction of heterozygotes and eventually inbreeding depression (Keller & Waller, 2002). The inbreeding rate in this study was slightly higher compared to Mauritia flexuosa populations from northern South America (Sander et al., 2018). These inbreeding coefficients were also higher compared to populations of another widespread palm species Euterpe edulis ( F IS = 0.12; Gaiotto, Grattapaglia, & Vencovsky, 2003).…”

“…Second, under the presence of null alleles, we would expect that some loci deviate from the Hardy–Weinberg equilibrium (Dubreuil et al., 2010), This, however, was not recovered in our study as all stands and seven out of eight loci analyzed deviated significantly from the Hardy–Weinberg equilibrium. Third, previous studies on Mauritia flexuosa already showed homozygote excess at different spatial scales (Melo et al., 2018; Sander et al., 2018). These arguments suggest that our genetic indexes mainly reflect true values linked with the biology of these populations rather than genotyping errors.…”

“…However, unsustainable overharvesting via uncontrolled felling of female individuals for fruit harvesting has strong negative impacts on its conservation (Rojas‐Ruiz et al, 2001). Additionally, palynological and genetic studies have highlighted the role of climatic shift during the Quaternary and river dynamics on the genetic structure of Mauritia flexuosa at the continental level (Lima, Lima‐Ribeiro, Tinoco, Terribile, & Collevatti, 2014; Melo, Freitas, Bacon, & Collevatti, 2018; Rull, 1998; Sander et al., 2018).…”

Channel network structure determines genetic connectivity of landward–seaward Avicennia marina populations in a tropical bay

“…Rabinowitz (1978) proposed that the interacting effects of water depth with species‐specific propagule traits (“tidal sorting”) might explain the differential distribution (zonation) of mangrove species along the tidal gradient. Similarly, the position of populations relative to open‐water channels and the spatial arrangement of these channels and their tidal currents may determine rates of hydrological connectivity and influence population genetic structure (Hughes et al., 2009; Pilger et al., 2017; Sander et al., 2018; Thomaz et al., 2016). However, while “riverscape genetics” is an active field of research and the importance of tidal inundation, dispersal traits, and establishment in determining mangrove forest structure (intertidal zonation) has been studied extensively (e.g., Clarke et al., 2001; Jiménez & Sauter, 1991; Rabinowitz, 1978; Sousa et al., 2007; Wang et al., 2019), few studies have linked these factors to the local (<10 km) and fine‐scale (i.e., within‐population) spatial genetic structure of mangroves.…”