Fungal farming social insects are a highly researched group of animals. Termites and ants are two of the most successful insects to farm fungus, and have been doing so for millions of years. Solitary insects cultivate fungus as well within galleries inside trees they invade. 15 years ago, for the first time, a non-insect animal was found cultivating fungus. Fungal farming snails represent the first group of organisms outside of the class Insecta to evolve this agricultural lifestyle. The symbiosis between both species has significantly enhanced each species fitness, so it looks like the small marine snail Littoraria irrorata will be interacting with coastal grasslands for generations to come.
Researchers Brian R. Silliman and Steven Y. Newell surveyed 16 marshes along 2,000 kilometers of southeastern Atlantic coastline to study and see the extent of this ecological interaction. These two scientists realized that most invertebrates in detritus based intertidal ecosystems primarily feed on the saprophytic fungi breaking down plant debris. With this understanding, they hypothesized that invertebrates that intentionally damage plant material may provide new substrate for fungi, which will enhance their own feeding. Cordgrass from the genus Spartina grows abundantly in these coastal marshes, and it is these intertidal grasses that these snails cultivate fungus on. The marine adapted ascomycete fungi that break down the cordgrass are from the genera Phaeosphaeria and Mycosphaerella.
Their initial hypothesis was confirmed by their coastal observations. Snails that seemed to be grazing on Spartina grasses were not consuming the plants tissue. Instead, these invertebrates were creating and maintaining longitudinal wounds that promote fungal invasion. These field observations also indicate that these snails defecate their nitrogen rich fecal matter on these plant wounds. Not only does this waste material contain macronutrients that promote fungal growth, but the snail’s poo actually contains undigested fungal hyphae that can colonize cordgrass wounds immediately after deposition.
This goes to show that a well-rounded ecological understanding can spark new hypotheses that leads into new discoveries. These researchers comprehended how these detritus-based ecosystems function, and then proposed ecological interactions likely to evolve over time. Both the fungi and these snails benefit from this interaction as these marine adapted fungi get easily dispersed to new stalks of cordgrass and receive nutrients from snail poop. The snails receive a reliable, carbohydrate rich fungal meal. A truly fascinating interaction.