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High epizoochorous specialization and low DNA sequence divergence in Mediterranean Cynoglossum (Boraginaceae): Evidence from fruit traits and ITS region

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Fruit morpho-anatomy and DNA sequence diversity in Euro-Mediterranean taxa of Cynoglossum and the closely related genera Solenanthus and Pardoglossum were analysed to assess the structural traits that promote dispersal through transport via the fur of mammals, and to evaluate the phylogenetic value of carpological variation in the group. Electron and light microscopy showed striking epizoochorous adaptations in characters of the pluricellular projections of the epicarp (glo chids), such as multiple apical hooks, conical shape, and finely tuberculate surface, as well as the heavy mineralization of the cell walls with especially silicon and calcium revealed by X-ray microanalysis. The attachment potential of nutlets to sheep fleece, estimated through a General Linear Model, was species-specific and relatively high in the taxa with small and light diaspores (>60%). ITS sequences from 29 specific and infraspecific accessions were poorly variable, with pairwise genetic distances ranging from 0.002 to 0.097 (mean 0.044). A comparative analysis of ITS sequence diversity in relation to the differ ent dispersal strategies in the four main Boraginaceae tribes revealed substantially higher levels of variation and interspecific genetic distances in the non-epizoochorous groups, including the Cynoglosseae genera Myosotis and Omphalodes. Bayesian and maximum parsimony tree construction suggested paraphyly of Cynoglossum due to the nested position of Solenanthus apenninus and Pardoglossum. Species-level relationships remained largely unresolved, preventing an estimation of the phylogenetic significance of fruit characters. Rapid spread across the Mediterranean region via epizoochory by wild mammals is possibly the primary cause for the lack of genetic divergence among species. During the Holocene, nomadic and transhumant pasture by domesticated herbivores has likely contributed to further spreading and mixing of previously isolated taxa, possibly causing events of homoploid hybridization and introgression. More variable molecular markers should be tested to better understand the impact of these processes in the evolutionary history of Cynoglossum and to solve relationships within Cynoglosseae.


Document Type: Research Article

Affiliations: 1: Università di Firenze, Dipartimento di Biotecnologie Agrarie, Sezione Botanica Ambientale ed Applicata, P. le Cascine 28, 50144 Firenze, Italy 2: Università di Firenze, Dipartimento di Biologia Evoluzionistica, Laboratori di Botanica, Via La Pira 4, 50121 Firenze, Italy

Publication date: 2011-08-01

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