title: Origin and evolution of Petrocosmea (Gesneriaceae) inferred from both DNA sequence and novel findings in morphology with a test of morphology-based hypotheses.
abstract: BACKGROUND
  Petrocosmea Oliver (Gesneriaceae) currently comprises 38 species with four non-nominate varieties, nearly all of which have been described solely from herbarium specimens. However, the dried specimens have obscured the full range of extremely diverse morphological variation that exists in the genus and has resulted in a poor subgeneric classification system that does not reflect the evolutionary history of this group. It is important to develop innovative methods to find new morphological traits and reexamine and reevaluate the traditionally used morphological data based on new hypothesis. In addition, Petrocosmea is a mid-sized genus but exhibits extreme diverse floral variants. This makes the genus of particular interest in addressing the question whether there are any key factors that is specifically associated with their evolution and diversification.
  
  
  RESULTS
  Here we present the first phylogenetic analyses of the genus based on dense taxonomic sampling and multiple genes combined with a comprehensive morphological investigation. Maximum-parsimony, maximum likelihood and Bayesian analyses of molecular data from two nuclear DNA and six cpDNA regions support the monophyly of Petrocosmea and recover five major clades within the genus, which is strongly corroborated by the reconstruction of ancestral states for twelve new morphological characters directly observed from living material. Ancestral area reconstruction shows that its most common ancestor was likely located east and southeast of the Himalaya-Tibetan plateau. The origin of Petrocosmea from a potentially Raphiocarpus-like ancestor might have involved a series of morphological modifications from caulescent to acaulescent habit as well as from a tetrandrous flower with a long corolla-tube to a diandrous flower with a short corolla-tube, also evident in the vestigial caulescent habit and transitional floral form in clade A that is sister to the remainder of the genus. Among the five clades in Petrocosmea, the patterns of floral morphological differentiation are consistent with discontinuous lineage-associated morphotypes as a repeated adaptive response to alternative environments.
  
  
  CONCLUSIONS
  Our results suggest that the lineage-specific morphological differentiations reflected in the upper lip, a functional organ for insect pollination, are likely adaptive responses to pollinator shifts. We further recognize that the floral morphological diversification in Petrocosmea involves several evolutionary phenomena, i.e. evolutionary successive specialization, reversals, parallel evolution, and convergent evolution, which are probably associated with adaptation to pollination against the background of heterogeneous abiotic and biotic environments in the eastern wing regions of Himalaya-Tibetan plateau.
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, 20 nanxincun, Beijing, 100093, China. qiuzhijing@gmail.com.|Key Laboratory of Southern Subtropical Plant Diversity, Fairylake Botanical Garden, Shenzhen & Chinese Academy of Sciences, Shenzhen, 518004, China. qiuzhijing@gmail.com.
authors.forename: Zhi-Jing
authors.initials: ZJ
authors.lastname: Qiu
authors.affiliation: Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650204, China. yuanxue@mail.kib.ac.cn.
authors.forename: Yuan-Xue
authors.initials: YX
authors.lastname: Lu
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, 20 nanxincun, Beijing, 100093, China. tiliaceae@sina.com.
authors.forename: Chao-Qun
authors.initials: CQ
authors.lastname: Li
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, 20 nanxincun, Beijing, 100093, China. dyhenry@126.com.
authors.forename: Yang
authors.initials: Y
authors.lastname: Dong
authors.affiliation: Boise State University, Department of Biological Sciences, Boise, ID, 83725-1515, USA. jfsmith@boisestate.edu.
authors.forename: James F
authors.initials: JF
authors.lastname: Smith
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, 20 nanxincun, Beijing, 100093, China. wangyz@ibcas.ac.cn.
authors.forename: Yin-Zheng
authors.initials: YZ
authors.lastname: Wang
mesh_terms: D001210:Asia, Southeastern; D005075:Biological Evolution; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D002681:China; D018742:DNA, Chloroplast / Q000235:genetics / Q000378:metabolism; D018744:DNA, Plant / Q000235:genetics* / Q000378:metabolism; D035264:Flowers / Q000033:anatomy & histology / Q000235:genetics; D007194:India; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D018515:Plant Leaves / Q000033:anatomy & histology / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D018742:DNA, Chloroplast; D018744:DNA, Plant; D010940:Plant Proteins