title: Ecological barriers to gene flow between riparian and forest species of Ainsliaea (Asteraceae).
abstract: Understanding the role of habitat-associated adaptation in reducing gene flow resulting in population differentiation and speciation is a major issue in evolutionary biology. We demonstrate a significant role for habitat divergence in species isolation between two naturally hybridizing riparian and nonriparian plants, Ainsliaea faurieana and A. apiculata (Asteraceae), on Yakushima Island, Japan. By analyzing the fine-scale population structure at six sympatric sites, we found that variations in leaf shape, geography, light conditions, and genotype were strongly correlated across riverbank-forest transitions. No evidence of effective gene flow was found between the two species across the majority of the transition zones, although the NewHybrid clustering analysis confirmed interspecific hybridization. However, a relatively high level of gene flow was observed across one zone with a more diffuse ecotone and intermediate flooding and light conditions, possibly generated by human disturbances. These results suggest that the barriers to gene flow between the riparian and forest species are primarily ecological. Additional common garden experiments indicated that the two species are adaptively differentiated to contrasting flooding and light environments. Overall, our study suggests that adaptations to different habitats can lead to the formation of reproductive isolating barriers and the maintenance of distinct species boundaries.
authors.affiliation: Graduate School of Human and Environmental Studies, Kyoto University, Yoshida, Nihonmatsu-cho, Sakyo-ku, Kyoto 606-8501, Japan. yuki.m@fs5.ecs.kyoto-u.ac.jp
authors.forename: Yuki
authors.initials: Y
authors.lastname: Mitsui
authors.forename: Naofumi
authors.initials: N
authors.lastname: Nomura
authors.forename: Yuji
authors.initials: Y
authors.lastname: Isagi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tobe
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Setoguchi
mesh_terms: D019659:Asteraceae / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics*; D017753:Ecosystem; D051456:Gene Flow; D005843:Geography; D006824:Hybridization, Genetic; D008027:Light; D010788:Photosynthesis; D018515:Plant Leaves / Q000033:anatomy & histology; D045483:Rivers; D014197:Trees / Q000145:classification / Q000235:genetics*