The evolutionary origins of aerial parasitism in Santalales

NICKRENT, D. L. & VIDAL-RUSSELL, R.

Charlottesville, Virginia, EE. UU.

Congreso; 9th. World Congress on Parasitic Plants; 2007

Molecular phylogenetic work in the sandalwood order (Santalales) has progressed to the point where multiple DNA sequences of nuclear and plastid genes are available for nearly all of the 146 genera. Moreover, phylogenetic methods have matured with the development of model-based methods such as maximum likelihood (ML) and Bayesian inference (BI) that more effectively deal with rate heterogeneity – an issue with some parasitic plant lineages. Past work showed that aerial parasitism evolved five times independently in Santalales, but the relative timing of these diversifications was not addressed. DNA sequences from five genes were obtained from 39 taxa representing all families in Santalales. These data were analyzed using ML and BI and time estimates were performed with a Bayesian relaxed molecular clock and penalized likelihood methods. The trees were calibrated using published fossil data from Santalales and an outgroup. These analyses showed that aerial parasitism first arose in Misodendraceae ca. 89 Mya and subsequently in Viscaceae (81 Mya), “Eremolepidaceae”(62 Mya), tribe Amphorogyneae in Santalaceae (53 Mya), and Loranthaceae (30 Mya). The rapid adaptive radiation and speciation in Loranthaceae coincides with the appearance of savanna biomes during the Oligocene. Reconstructing the character “parasite mode” on the tree suggests that all lineages except Misodendraceae evolved from ancestors that were polymorphic for either root or stem parasitism. Features found in more derived aerial parasites, such as the squamate habit, unisexual flowers, and loss of chlorophyll, have evolved independently and thus represent convergences and parallelisms.