Phylogenetic position of Neotropical Bursera -specialist mistletoes: the evolution of deciduousness and succulent leaves in Psittacanthus (Loranthaceae)

Abstract

Background: The phylogenetic relationships of the Bursera -host specialist Psittacanthus nudus , P. palmeri and P. sonorae (Loranthaceae) remain uncertain. These mistletoe species exhibit morphological and phenological innovations probably related to their dry habitats, so that determining their phylogenetic position is key to the understanding of factors associated with the morphological evolution within Psittacanthus .Questions: (1) Is the evolution of some morphological innovations in the Bursera -host specialists associated with the ecological conditions linked to host diversification? (2) Does time of diversification in both lineages coincide?Study species: Fourteen species of Psittacanthus .Methods: Sequences of nuclear (ITS) and plastid ( trnL-trnF ) markers are analyzed with Bayesian inference, maximum likelihood and maximum parsimony methods, and molecular dating under a Bayesian approach estimated to elucidate the phylogenetic position and divergence timing of the Bursera -host specialists.Results: The Bursera -host specialists form a strongly supported clade, named here the ‘ Bursera group’. The divergence time for the Bursera -host specialists was estimated at 7.89 Ma. Interestingly, phylogenetic relationships between P. nudus and P. palmeri , as currently circumscribed, were not fully resolved, making P. palmeri paraphyletic.Conclusions: Based on these results, the plants collected by type locality of P. nudus in Honduras should be named P. palmeri . The seasonal deciduousness of P. palmeri (including P. nudus ) and morphology of P. sonorae (small size, fleshy leaves) are clearly adaptations to dry ecosystems where these species have lived for a long time. In parallel, the evolutionary history of these mistletoes seems to be correlated with the evolutionary history and diversification patterns of Bursera .