Level of Fly Vector Mutualism Depends on Epichloë Reproductive Strategy
Dr. Thomas Bultman, Biology
Botanophila flies act as pollinating predators of sexually reproducing Epichloë fungi, and were found to be the main vectors of fungal gametes; however, other vectors and methods of fertilization have been suggested. We hypothesized that this discrepancy is due to different types of reproductive modes used by different species of Epichloë. We hypothesized that type I fungi (which only reproduce sexually) will depend less on Botanophila flies for spore transfer, as it is more risky for these fungi if the fly fails to fertilize. However, type II fungi (which reproduce both sexually and asexually) can afford to take the risk of the fly failing, since they have a “backup” mode of reproduction (asexual). We observed the interaction between Botanophila and Epichloë typhina (a type I species) at our field site in the forest of Phalempin, France to determine the level of dependence between the fly and fungus. As expected, egg numbers on the stromata were high at the beginning of the study, but dropped off as eggs hatched and larval numbers increased. Feeding by both fly larvae and other fungivores increased over the study period. Unlike past studies from our lab, that found that the fly was the main vector for cross fertilization of type II fungi, we found no net benefit to the fungus of having the fly visit Epichloë typhina. This is consistent with studies published by other labs and with our hypothesis that the mutualism of Botanophila is based on reproductive mode.
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