Abstract
Variations in the frequency and extent of hybridization among mixed populations located in the same contact zone provide natural laboratories for the study of extrinsic reproductive isolation maintaining species integrity. In this study, we examined the pattern of hybridization between L. japonicum and L. stellipilum among mixed populations in different localities of a contact zone. The genetic structures from three sympatric populations and six mixed populations in the hybrid zone, and five reference populations far from the contact zone, were characterized using 10 neutral nuclear microsatellite markers. Evidence from genetic distance-based clustering analysis, the frequency distribution of admixture proportion values, and the hybrid category assignment approaches indicated that the frequency and extent of hybridization varied considerably among populations in the contact zone between L. japonicum and L. stellipilum. One likely explanation is that variation in exogenous (ecological) selection among populations might contribute to differences in frequency and extent of hybridization. The present study will facilitate future research exploring the evolution of reproductive isolation between L. japonicum and L. stellipilum.
Highlights
Natural hybridization is most often the result of secondary contact by range expansion between previously isolated populations or may arise via primary intergradation along an environmental gradient during the process of parapatric speciation [1]
To gain a better understanding of whether the frequency of hybridization between L. japonicum and L. stellipilum can be influenced by local conditions, we examined the patterns of hybridization between the two species among mixed populations in different localities of a hybrid zone
The overall genetic differentiation was considerable in the comparison between L. japonicum populations and L. stellipilum populations with FST ranging from 0.29 to 0.37 (S1 Table)
Summary
Natural hybridization is most often the result of secondary contact by range expansion between previously isolated populations or may arise via primary intergradation along an environmental gradient during the process of parapatric speciation [1]. Natural hybridization is a widespread phenomenon in plant species and occurs in 40% of vascular plant families [2,3]. The frequency of natural hybridization in plants varies among families, genera, and species pairs [4]. The frequency of hybrid formation between species pairs can reflect the strength of reproductive isolation barriers between species and the stages in their speciation process [5,6]. Hybridization frequency varies at the species level because the period required for the PLOS ONE | DOI:10.1371/journal.pone.0116411. Hybridization frequency varies at the species level because the period required for the PLOS ONE | DOI:10.1371/journal.pone.0116411 March 4, 2015
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