Biodiversity of cactophilic microorganisms in western Argentina: community structure and species composition in the necroses of two sympatric cactus hosts

• The saprotrophic microbial community in the necroses of two cacti are investigated.
• Both cacti live in sympatry and are exploited by two cactophilic Drosophila.
• The core community is composed of six yeasts or yeast-like organisms, one green-alga and one filamentous fungi.
• The community of Trichocereus terscheckii is a subset of that of Opuntia sulphurea.
• Ecological and chemical interactions with vectors and hosts are proposed to explain this pattern.

The cactus-yeast-Drosophila system is a model system in evolutionary biology, and the participating saprotrophic microorganisms represent one of the most thoroughly studied microbial communities. However, much of the cactus-dominated regions of South America, home to endemic versions of this classical system, remain understudied. A combined morpho-physiological and molecular approach was employed to identify the fungal members of the cactus-yeast-Drosophila system in western Argentina. We identified twenty one species of saprotrophic organisms in the necroses of Opuntia sulphurea and Trichocereus terscheckii in a region of sympatry, where both cacti are exploited by cactophilic Drosophila. After excluding opportunistic isolates, we determined that the saprobe community of O. sulphurea was composed of eight species (including the first consideration of filamentous fungi as community members), whereas the community of T. terscheckii represented a subgroup of the former. We explain this nested pattern by considering the physiological and ecological attributes of both hosts and vectors involved.