title: Leaf anatomy of two reciprocally non-monophyletic mountain plants (Heliosperma spp.): does heritable adaptation to divergent growing sites accompany the onset of speciation?
abstract: Evolution is driven by natural selection, favouring individuals adapted in phenotypic traits to the environmental conditions at their growing site. To shed light on ecological and (epi-) genetically based differentiation between Heliosperma pusillum and Heliosperma veselskyi, two reciprocally non-monophyletic, but morphologically and ecologically divergent species from the south-eastern Alps, we studied various leaf anatomical traits and investigated chloroplast ultrastructure in leaves of the two species grown either in their natural habitat or in a common garden. The alpine H. pusillum occurs in open, wet rock habitats, whereas its close relative H. veselskyi is restricted to dry, shady habitats below overhanging rocks in the montane belt. H. pusillum exhibited higher thickness of leaves and palisade layers as adjustments and/or adaptations to higher irradiance and a higher stomatal area index reflecting better water availability. Traits were adjusted plastically, but differed between species grown in a common garden, suggesting that the differentiation between the two species is not solely based on phenotypic plasticity but also has a genetic basis. Our study thus supports the hypothesis that differentiation between the highly interfertile species is likely driven by natural selection.
authors.affiliation: Institute of Botany, University of Innsbruck, Innsbruck, Austria. clara.bertel@uibk.ac.at.
authors.forename: Clara
authors.initials: C
authors.lastname: Bertel
authors.affiliation: Institute of Botany, University of Innsbruck, Innsbruck, Austria.
authors.forename: Peter
authors.initials: P
authors.lastname: Schönswetter
authors.affiliation: Institute of Botany, University of Innsbruck, Innsbruck, Austria.
authors.forename: Božo
authors.initials: B
authors.lastname: Frajman
authors.affiliation: Institute of Botany, University of Innsbruck, Innsbruck, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Holzinger
authors.affiliation: Institute of Botany, University of Innsbruck, Innsbruck, Austria.
authors.forename: Gilbert
authors.initials: G
authors.lastname: Neuner
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D029748:Caryophyllaceae / Q000033:anatomy & histology* / Q000235:genetics; D002736:Chloroplasts / Q000648:ultrastructure*; D017753:Ecosystem; D046529:Microscopy, Electron, Transmission; D018515:Plant Leaves / Q000033:anatomy & histology*
keywords: Adaptation; Alpine plants; Environmentally induced speciation; Leaf anatomy; Leaf ultrastructure