Native to Japan, Wickerhamomyces anomalus is a Saccharomycetes yeast that is found growing on the inside of bamboo. Upon closer investigation, researchers discovered that this fungus occurs only when a lizard beetle larva (Doubledaya bucculenta) inhabit the same bamboo plant. With this, yet another example of fungal agriculture has been described, only this time coming from a solitary insect.
Lizard beetle, Doubledaya bucculenta (A), bamboo fibre plug (B,C). Toki et al. 2012.
It all starts when female lizard beetles chew a hole in bamboo plants that have recently died. They then oviposit an egg in the hollow bamboo, and plug the entrance hole with bamboo fibers. While their offspring develops, the fungus featured in this week’s edition of Fungi Friday also grows. Cells of W. anomalus are vectored by the adult females and make their way into the hollow bamboo via specialized fungal transport organs called mycangia. This interaction is without a doubt a specific mutualism that clearly shows how two species that enhance each other’s fitness co-occur for millions of years.
Doubledaya bucculenta mycangia. M=mycangium; O=ovipositor; Y= yeast cells; AT= anterior; DO=dorsal; PT=posterior; VE=ventral. Toki et al. 2012.
Overtime, insects that specialize in fungal agriculture evolve mycangium. These structures are vital to their lifestyle, because without a means of fungal transport, areas of cultivation would be extremely localized, and the distribution of the insect would be infinitesimally small. Mutualisms like this have a prominent role in a species evolutionary trajectory. This is realized when looking at the morphology of non-agricultural related cousins of the lizard beetle (subfamily Languriinae). They haven’t evolved a symbiosis with fungi, thus have not evolved mycangium.
Doubledaya bucculenta larva feeding on colonies of Wickerhamomyces anomalus (arrows). Toki et al. 2012.
Laboratory studies carried out by Wataru Toki and his team in 2012 revealed that when lizard beetle larva was placed in bamboo without the Saccharomycetes yeast, development came to an abrupt halt. These Japanese scientists discovered that these larvae depend on the fungal growth as a source for food, so it makes sense that in the absence of food, the insect can’t grow.
(E) Steril bamboo with pith tissue (arrows). (F) colonies of Wickerhamomyces anomalus. (G) individual yeast cells, note the one budding asexually. Toki et al. 2012.
Wickerhamomyces anomalus is never found in nature without its insect counterpart. This exemplifies an intimate species interaction that both parties depend on. Besides being a food source for the developing insects, I’m sure there are more undiscovered interactions to be found. The colonies of yeast growing within the bamboo probably provide some protection against opportunistic bacteria, because these fungi readily compete for space in these microhabitats. It always excites me when I find how two species can unite in a symbiosis and alter each other’s evolutionary trajectory. Especially when there’s an agricultural system in the mix.