The origin of the cactus-yeast community.

The yeast community found in decaying cactus stems and cladodes is stable in terms of species membership and is similar in composition over space and time. The ecological origins of the three core and four common species in the assemblage were inferred by mapping yeast habitats onto a phylogeny of yeasts reconstructed from rDNA sequences. The members of the community belong to distinct clades and consequently have independent origins. The inferred evolutionary pathways of the taxa originate in either tree-flux or decaying fruit habitats and lead to decaying Opuntia cladode and columnar stem habitats. The reasons for the polyphyletic origins of the cactus-yeast community could be due to unique aspects of cactus chemistry, environmental extremes, vector association and interactions among the members.