Genetic structure reveals a history of multiple independent origins followed by admixture in the allopolyploid weed Salsola ryanii

Abstract

It has recently become clear that many invasive species have evolved in situ via hybridization or polyploidy from progenitors which themselves are introduced species. For species formed by hybridization or polyploidy, genetic diversity within the newly formed species is influenced by the number of independent evolutionary origins of the species. For recently formed species, an analysis of genetic structure can provide insight into the number of independent origin events involved in the formation of the species. For a putative invasive allopolyploid species, the number of origins involved in the species formation, the genetic diversity present within these origins, and the level of gene flow between independent origins determines the genetic composition of the neospecies. Here we analyze the genetic structure of the newly formed allopolyploid species, Salsola ryanii, a tumbleweed which evolved within the last 20–100 years in California. We utilize the genetic structure analysis to determine that this new species is the result of at least three independent allopolyplodization events followed by gene flow between the descendants of independent origins.

Gene flow in Argentinian sunflowers as revealed by genotyping‐by‐sequencing data

“…A recent special issue in this journal (Ellstrand & Rieseberg, 2016) highlighted the potentially important applied consequences of gene flow. These included genetic rescue (Fitzpatrick et al, 2016), demographic or genetic swamping (Todesco et al, 2016), transgene escape (Lu et al, 2016), and the evolution of weedy or invasive taxa (Welles & Ellstrand, 2016). Gene flow between wild and domesticated species can be especially problematic because of the likely imbalance in population size between the crop and nearby wild relative populations and because some domestication traits also contribute weedy life-history behaviors (Ellstrand et al, 2013).…”

Segmental allopolyploidy in action: Increasing diversity through polyploid hybridization and homoeologous recombination

“…However, genetic diversity is also an issue for allopolyploids, because polyploid formation creates a genetic bottleneck. The polyploidy bottleneck can be mitigated by multiple origins involving different genotypes (Soltis et al., ), and gene flow between the polyploids of different origins and lineages (e.g., Soltis and Soltis, , ; Doyle et al., ; Welles and Ellstrand, ). However, recombination among subgenomes can lead to loss of genetic diversity, even in allopolyploids (Ramsey and Schemske, ; Gaeta and Pires, ; Wendel, ), let alone in autopolyploids, where random pairing among two or more sets of homologous chromosomes is expected; the same problem can occur in plants with intermediate pairing behavior termed segmental allopolyploids (Stebbins, ).…”

Population structure and phylogeography ofElymus mutabilisand its genetic relationships withE. transbaicalensis(Poaceae)

“…Multiple polyploidization events from the same progenitor taxa may lead to cryptic speciation forming distinct lineages that are not accompanied by clear morphological differentiation (Soltis et al 2010). Recurrent formations of polyploid species from the same diploid parental taxa are considered to be more common than single events and may be an important source of increased genetic variation in polyploids depending on the contribution from diploid progenitors (Symonds et al 2010, McAllister and Miller 2016, Welles and Ellstrand 2016). The case of E. mutabilis and E. transbaicalensis is a good example of a cryptic relationship.…”