Higher fungi produce large structures known as mushrooms or fruiting bodies. This morphological adaptation in the division Basidiomycota and Ascomycota evolved to enhance spore production and dispersal. Being elevated just a few centimeters above the forest floor increases the probability of a released spore to hitch a free ride on rising air current. Even above the grounds stationary boundary layer, the chance of a spore to land on a suitable substrate is nearly infinitesimal. For this reason, higher fungi produce massive amounts of spores to ensure enough of them find a fitting area to germinate.
Some fungi just happen to complete beasts in spore release. The 250+ species of Ganoderma are those freaks of nature. Ganoderma applanatum has been scientifically shown to release 30 billion spores a day! Even more impressive, it does this throughout the warmer 6 months of the year. 180 daysX30,000,000,000 spores/day= a number none of us actually understand. Even from a fungal perspective, this seems like overkill, right? When patterns like these arise, we can take a look at the underlying biology and interpret why some species do what they do. Because resources are hard to come by living from the forest floor, evolution will not favor wasteful species. Even the untrained eye can recognize plumes of spores exiting the fungus.
Spore plumes from G. applanatum used with permission from In Defense of Plants.
So why the ridiculous number of spores? Well, Ganoderma applanatum is a wound parasite that is specialized in infecting beech trees (Fagus sylvatica). Although it is sometimes found infecting other trees, it is indeed a specialist. Within a relatively wide range of temperatures and moisture content, most species spores will germinate on the expansive forest floor. On the other side of the spectrum, the spores of G. applanatum must land on the wound of a specific living tree. The area of possible germination is several orders of magnitude smaller for G. applanatum which is why it produces several orders of magnitude more spores compared to other fungi. Even still, this spore finding a suitable host is a shot in the dark. There may be another reason why these fungi fill the air with their spores.
This tree parasite actually hosts a small midge-like fly called the yellow flat-footed fly (Agathomyia wankowiczii). The eggs of this insect are laid on the surface of G. applanatum, where it hatches and burrows its way to the interior. Some say this yellow flat-footed fly is a parasite, because it consumes fungal tissue that may have took an entire season to grow. Now this is only speculation because there is little information on this insect out there, but once these larvae mature into adults they must be covered in spores. They may act as a vector, transferring spores to wounded trees because many forest insects find the liquid flowing from tree wounds irresistible.
I only find signs of this insect on large fruiting bodies of G. applanatum. Females most likely select large fruiting bodies to protect their offspring from the elements, and to ensure they’re provided with enough food to mature. These insects are only found maturing in these specific fungi, so surely something more intricate may be going on. If large individuals are selected by females more, than there most definitely is a directional selection towards forming larger fruiting bodies. The larger fruiting bodies are made up of more spore bearing structures called pores. The immense number of spores released by G. applanatum might just be a byproduct of growing large to attract its insect mutualist. Again this is speculation, but with little information on this insect and the fact that it’s only found laying eggs on G. applanatum, I’m allowed to entertain certain ideas.
Agathomyia wankowiczii oviposition on G. applanatum. Published under.
That’s the glory of ecology. To see patterns in nature and to come up with an answer that helps describe what we see. We know a lot, but we clearly don’t know everything. This brings mystery and wonder to a fast moving anthropogenic world. Nature becomes more special, the deeper you dig, the more you learn.