Extinction has reduced the Achatinella genus of tree snails from approximately 41 species to just 10 species. The last lonely individual of the species Achatinella apexfulva has recently died and there are less than ten known individuals of A. fulgens in the wild. To minimize the risk of extinction of surviving species an ex situ breeding facility, the Hawaiian Tree Snail Conservation Laboratory, has maintained subpopulations of the snails since the late nineteen-eighties. However, despite the absence of predators these ex situ populations have not flourished. Managers are anxious to improve lab conservation strategies, because wild stocks of these unique animals are quickly declining. We used non-invasive methods and surrogate species to explore how the ex situ diet of these critically endangered species differs from their wild diet and could be enhanced.
Staff at the ex situ culture facility replicate the wild diet of snails by making frequent expeditions into the forest to collect bags of native foliage from which the captive snails can graze epiphytic fungi. The diet of captive snails is also supplemented with a monoculture of the fungus Cladosporium, which is provided to snails on disks of nutrient agar. We used DNA sequencing of feces to determine if the Cladosporium fungus that is used to supplement the diet of captive snails is a large component of their diet. It turned out that this isn’t really a “supplemental” diet, but instead dominates the diet (~38%). Although Cladosporium is a large component of the snail’s wild diet, but by “large” I mean it makes up ~1.5% of the fungus detected in the guts of the snail, so considerably less than 38%.
Studies had been conducted with snails where they were given the option of eating a fungal species or not, i.e. “single choice” experiments. These experiments determined that snails eat almost any fungus. Our eDNA studies also indicated that snails tended to indiscriminately consume any fungus available on their host tree. We wanted to use a controlled experiment to test if snails have food preferences. We didn’t use the federally endangered Achatinella snails for this, but substituted a species of tree snail in the same subfamily as them, an Auriculella. We were reluctant to use any critically endangered species because the controlled experiment involved putting multiple snails in little glass enclosures and filming them over 24 hours.