Gene flow between nascent species: geographic, genotypic and phenotypic differentiation within and between Aquilegia formosa and A. pubescens

Abstract

Speciation can be described as a reduction, and the eventual cessation, in the ability to interbreed. Thus, determining how gene flow differs within and between nascent species can illuminate the relative stage the taxa have attained in the speciation process. Aquilegia formosa and A. pubescens are fully intercompatible, yet occur in different habitats and have flowers specialized for pollination by hummingbirds and hawkmoths, respectively. Using 79 SNP loci, we genotyped nearly 1000 individuals from populations of both species in close proximity to each other and from putative hybrid zones. The species shared all but one SNP polymorphism, and on average, allele frequencies differed by only 0.14. However, the species were clearly differentiated using Structure, and admixed individuals were primarily identified at putative hybrid zones. PopGraph identified a highly integrated network among all populations, but populations of each species and hybrid zones occupied distinct regions in the network. Using either conditional graph distance (cGD) or Fst/(1-Fst), we found significant isolation by distance (IBD) among populations. Within species, IBD was strong, indicating high historic gene flow. IBD extended approximately 100 km in A. pubescens and 30 km in A. formosa. However, IBD between the species was very weak and extended only a few km beyond hybrid zones, suggesting little recent gene flow. The extensive sharing of SNP polymorphisms between these species suggests that they are very early in the speciation process while the low signal of IBD suggests that they have largely ceased gene exchange.

Lack of spatial structure for phenotypic and genetic variation despite high self-fertilization in Aquilegia canadensis (Ranunculaceae)

“…Yang and Hodges (2010) documented a progressive decrease in F through the life cycle in A. formosa and A. pubescens consistent with higher mortality of selfed than outcrossed offspring. Both species also exhibit extensive gene flow and isolation by distance among populations separated by tens of kilometers (Noutsos et al 2014). Similar results have also been documented in other species.…”

The geography of divergence with gene flow facilitates multitrait adaptation and the evolution of pollinator isolation inMimulus aurantiacus

“…; Alder and Doadrio ; Noutsos et al. ). Moreover, our F ST analysis does not support a conclusion of allopatric divergence followed by recent secondary contact.…”

netview p: a network visualization tool to unravel complex population structure using genome‐wide SNPs

“…; Noutsos et al . ). Network analyses lack many of the assumptions of model‐based approaches, such as underlying population models or prior geographical clustering (Kivelä et al .…”

“…In the graph theoretical approach, the data is depicted by the topology of a network. In a population genetic context, multilocus genotype data can be used to construct networks of individuals (Moalic et al 2011;Neuditschko et al 2012) or predetermined populations (Dyer & Nason 2004;Rozenfeld et al 2008;Noutsos et al 2014). Network analyses lack many of the assumptions of model-based approaches, such as underlying population models or prior geographical clustering (Kivel€ a et al 2015) and can depict the connectivity and information flow within and between populations (Rozenfeld et al 2008;Neuditschko et al 2012;Kivel€ a et al 2015).…”

“…Network analyses lack many of the assumptions of model-based approaches, such as underlying population models or prior geographical clustering (Kivel€ a et al 2015) and can depict the connectivity and information flow within and between populations (Rozenfeld et al 2008;Neuditschko et al 2012;Kivel€ a et al 2015). Their use for population analysis has been exemplified in the desert cactus Lophocereus schottii (Dyer & Nason 2004), the metapopulation system of the seagrass Posidonia oceania (Rozenfeld et al 2008), a hybridization study of two microalgae of the genus Fucus (Moalic et al 2011) and diverging species of the plant Aquilegia (Noutsos et al 2014).…”