Abstract
Seed dispersal is crucial to gene flow among plant populations. Although the effects of geographic distance and barriers to gene flow are well studied in many systems, it is unclear how seed dispersal mediates gene flow in conjunction with interacting effects of geographic distance and barriers. To test whether distinct seed dispersal modes (i.e., hydrochory, anemochory, and zoochory) have a consistent effect on the level of genetic connectivity (i.e., gene flow) among populations of riverine plant species, we used unlinked single-nucleotide polymorphisms (SNPs) for eight co-distributed plant species sampled across the Rio Branco, a putative biogeographic barrier in the Amazon basin. We found that animal-dispersed plant species exhibited higher levels of genetic diversity and lack of inbreeding as a result of the stronger genetic connectivity than plant species whose seeds are dispersed by water or wind. Interestingly, our results also indicated that the Rio Branco facilitates gene dispersal for all plant species analyzed, irrespective of their mode of dispersal. Even at a small spatial scale, our findings suggest that ecology rather than geography play a key role in shaping the evolutionary history of plants in the Amazon basin. These results may help improve conservation and management policies in Amazonian riparian forests, where degradation and deforestation rates are high.
Highlights
The proportion of total genetic variability that resides among populations provides a measure of the evolutionary processes acting within species (Holsinger and Weir, 2009)
After additional quality filtering, the total numbers of unlinked single-nucleotide polymorphisms (SNPs) used in the genomic analyses were 36,768 for A. schomburgkii, 39,747 for A. paraense, 10,595 for B. aequinoctialis, 34,265 for P. kerere, and 28,121 for T. pyramidatum
For wind-dispersed plant species, no significant differences among the genetic diversity estimates were observed, whereas among the water-dispersed plant species, those estimates were significantly higher for A. paraense than for P. kerere; among the animal-dispersed plant species, the estimates were significantly lower for A. longifolia than for P. spinosa and P. lupulina (Figure 2)
Summary
The proportion of total genetic variability that resides among populations (i.e., population genetic differentiation expressed by FST; Wright, 1943) provides a measure of the evolutionary processes acting within species (Holsinger and Weir, 2009). Seed dispersal mediated by animals should prevent population divergence, reduce inbreeding, and increase the levels of genetic diversity (e.g., Hamrick et al, 1993; Hamrick and Godt, 1996; Nybom and Bartish, 2000; Nybom, 2004; Vieira et al, 2010; Giombini et al, 2017; but see Thiel-Egenter et al, 2008). These general expectations are based on dispersal across a continuous landscape, and it is unclear how those expectations translate into dispersal propensities across river barriers. The relative permeability of a river barrier to gene flow as a function of species-specific traits is even less clear
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