Long-term persisting hybrid swarm and geographic difference in hybridization pattern: genetic consequences of secondary contact between two Vincetoxicum species (Apocynaceae–Asclepiadoideae)

Abstract

BackgroundDuring glacial periods, glacial advances caused temperate plant extirpation or retreat into localized warmer areas, and subsequent postglacial glacial retreats resulted in range expansions, which facilitated secondary contact of previously allopatric isolated lineages. The evolutionary outcomes of secondary contact, including hybrid zones, dynamic hybrid swarm, and resultant hybrid speciation, depends on the strengths of reproductive barriers that have arisen through epistatic and pleiotropic effects during allopatric isolation. The aim of this study was to demonstrate refugia isolation and subsequent secondary contact between two perennial Asclepioid species and to assess the genetic consequences of the secondary contact. We modeled the range shift of two ecologically distinct Vincetoxicum species using the species distribution model (SDM) and assessed the genetic consequences of secondary contact by combining morphological and genetic approaches. We performed morphometric analysis (592 individuals) and examined 10 nuclear microsatellites (671 individuals) in V. atratum, V. japonicum, and putative hybrid populations.ResultsMultivariate analysis, model-based Bayesian analysis, and non-model-based discriminant analysis of principal components confirmed the hybridization between V. atratum and V. japonicum. High pollen fertility and a lack of linkage disequilibrium suggested that the hybrid populations may be self-sustaining and have persisted since V. atratum and V. japonicum came into contact during the post-glacial period. Moreover, our findings show that the pattern of hybridization between V. atratum and V. japonicum is unidirectional and differs among populations. Geographically-isolated hybrid populations exist as genetically distinct hybrid swarms that consist of V. atratum-like genotypes, V. japonicum-like genotypes, or admixed genotypes. In addition, Bayesian-based clustering analysis and coalescent-based estimates of long-term gene flow showed patterns of introgressive hybridization in three morphologically ‘pure’ V. japonicum populations.ConclusionIn this study, we demonstrated that climatic oscillations during the Quaternary period likely led to species range shift and subsequently secondary contact. Hybrid populations may be self-sustaining and have persisted since V. atratum and V. japonicum came into contact during the post-glacial period. Pattern of hybridization between V. atratum and V. japonicum is unidirectional and differs among populations. We concluded that these differences in the genetic consequences of secondary contact are caused by historical colonization processes and/or natural selection.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0587-2) contains supplementary material, which is available to authorized users.

Pleistocene glacial cycles drove lineage diversification and fusion in the Yosemite toad (Anaxyrus canorus)

“…) breakdown of postmating barriers, with evidence of temporal stability in several cases (e.g., Li et al. ). Intraspecific lineage fusion is particularly likely when environmental heterogeneity between lineages is minimal (Seehausen ; Seehausen et al.…”

“…), often with evidence that lineages are temporally stable (e.g., Li et al. ). Regardless of whether early‐generation hybrids have reduced fertility or reproductive success, subsequent generations can still form a stable lineage (Arnold et al.…”

Pheromones and Other Semiochemicals for Monitoring Rare and Endangered Species

“…These studies have demonstrated that information from pheromone-based trapping during a single field season generally can surpass the known information about most rare species several times over, and that existing records often provide an underestimation of their true distributions. Pheromones also have been used for systematic DNA sampling for phylogeographic studies of E. ferrugineus (Oleksa et al 2015) and the Spanish moon moth G. isabellae (Mari-Mena et al 2016). In parallel with monitoring for conservation purposes, monitoring systems with pheromones and other semiochemicals support the detection of invasive pest species at low densities (Liebhold et al 2016), including monitoring their range expansion (Liebhold and Bascompte 2003; Suckling et al 2014), and the effectiveness of eradication efforts (Kean and Suckling 2005; Kikkert et al 2006; Lance and Gates 1994).…”

“…Pheromones have been used sporadically by collectors and conservationists in their search for rare and cryptic species, for example by using live females to attract males (Mari-Mena et al 2016), or by utilizing single synthetic pheromone components or partial pheromone blends (Buda et al 1993). During the last 10–15 years, however, increasing attention has been directed towards exploiting the powerful attraction of insect pheromones as monitoring tools in biodiversity and conservation research.…”

Crossing species boundaries : the hybrid histories of the true geese

“…These two scenarios are not always mutually exclusive: for example, ancient hybridization might be followed by rapid diversification which in turn leads to extensive hybridization among the resulting species. During the formation of a syngameon, the interacting species essentially form a single gene pool due to high levels of gene flow and can be seen as hybrid swarms (Arnold, 1997, Li et al, 2016b, Wiens et al, 2006.…”