Gene flow contributes to genetic diversity of tetraploid populations of the North American plant genusHoustonia(Rubiaceae)

Abstract

Polyploids are thought to harbor more genetic diversity than diploids, despite the genetic bottleneck they experience upon formation. Identifying the means by which polyploids become more genetically variable can advance our understanding of the evolutionary trajectories of polyploid lineages. Gene flow is one such mechanism that can contribute to polyploid genetic diversity. Here, we used microsatellite markers to measure genetic diversity and to estimate gene flow among closely related diploid and tetraploid species of the North American plant genus Houstonia section Amphiotis. We found that tetraploid populations were more genetically variable when compared to diploid populations and that gene flow (admixture) occurred more often among tetraploid populations than among diploids. In addition, we provide evidence to support previous reports that autopolyploidy is the likely mode of polyploid formation in this group. We suggest that gene flow among closely related species, particularly among tetraploid populations, has likely contributed to the genetic diversity levels of tetraploid lineages of Houstonia species.

Pure polyploidy: Closing the gaps in autopolyploid research

“…This process can enhance the genetic diversity of a nascent polyploid population and potentially mitigate the consequences of inbreeding among a small number of autopolyploids (Bretagnolle & Thompson, 1995). The evolutionary importance of gene flow between diploids and tetraploids was noted by Stebbins (1971), and the contributions of intercytotype gene flow on genetic diversity have since been reported in autopolyploid Dactylorhiza maculata (Ståhlberg, 2009), Houstonia (Glennon & Church, 2015), and Larrea tridentata (Laport et al, 2016). Selection on new autopolyploids may therefore be complex, with potentially opposing pressures-complete reproductive isolation from diploid progenitors (through prezygotic or postzygotic mechanisms) will counteract the deleterious effects of MCE by preventing often-unsuccessful intercytotype mating, but maintaining reproductive overlap with diploids may provide the benefit of increased genetic diversity through rare introgression via unreduced gametes.…”