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

Publication Type:Journal Article
Year of Publication:2011
Authors:Selvi, F., A. Coppi, L. Cecchi
Start Page:969
Keywords:Boraginaceae; Cynoglossum; epizoochory; fruit morphology; ITS sequences; phylogeny; seed dispersal; systematics

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 apen-
ninus 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.


Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith