Mutualistic and parasitic interactions betweenPhorbiaflies andEpichloe: convergence between a fungus and entomophilous angiosperms

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Abstract
During egg laying, Phorbia flies transport spermatia between individuals of their heterothallic fungal host Epichloe. Flies provide a service ecologically analogous to pollination. As a guide for studying the ecology and evolution of this unusual fungus – insect interaction, I propose that it has converged with angiosperm – entomophilous insect systems in general, and more specifically with highly coevolved pollinating seed parasite – angiosperm systems. I document similarities with insect pollination systems in general that include primary dependence by Epichloe on animal vectors, a color change of the fruiting structure following cross-fertilization, rewards provided to animal vectors, and exploitation by third party species that use rewards offered by the fungus but provide no payment for the rewards. Furthermore, the fungus – insect interaction shows several similarities with coevolved pollinating parasite systems. First, the interaction contains a mix of mutualism and parasitism with the net effect being positive for both partners. Second, flies display a specific behavior that ensures cross-fertilization of Epichloe. Third, the interaction is symbiotic and appears species specific and obligate for the interactants. Under the convergent evolution hypothesis, I discuss selection pressures that could have operated to produce ecologically analogous interactions among distantly related taxa of insect pollinated angiosperms and Epichloe. Key words: convergent evolution, Epichloe, mutualism, parasitism, Phorbia, pollination.