Australia has the world's only fungus-growing, eusocial, wood-eating weevil
(writing in progress)
Australia is an odd continent in that it lacks any fungus-culturing termites or ants.
Fungus-culturing termites (Isoptera: Termitidae: Macrotermitidae) occur in Africa and Asia. Fungus-culturing ants occur in the Americas.
It is easy to assume that the lack of any fungus-culturing, colonial insect in Australia is owing to an accident of history: the relevant lineages failed to reach the island continent. However, this does not acknowledge the potential for fungus-culturing to evolve in convergence, in different lineages, in Australia.
In this Post I give an example undermining any accidental explanation for the lack of fungus-culturing by eusocial insects (e.g. termites and ants) in Australia, owing to either
- geographical barriers (usually invoked in the case of the termites), or
- phylogenetic constraints (usually in the case of the ants).
As it turns out, Australia is the only continent on Earth in which a weevil (Coleoptera: Curculionidae: Austroplaytpus incompertus) has evolved eusociality within the context of fungus-culturing in order (indirectly, as in termites) to consume wood.
Although many weevils have evolved to consume wood and bark, this is the only one so far documented that approaches the business of consuming wood in a way essentially similar to the macrotermitine termites, in the sense of both growing fungus in wood and becoming eusocial. (The analogy with the fungus-growing ants of South America is of course limited because those ants consume leaves and soft litter and invertebrate frass rather than wood; but these ambrosia beetles seem to be particularly diverse and prominent in South America, where eusociality has yet to be discovered in weevils.)
Please see the two Wikipedia sites below, plus a study showing that fungus-growing wood-consuming weevils (albeit not eusocial) live in the wood of the pea, Virgilia oroboides.
On all continents, weevils have adopted the habit of growing fungi in wood. There are about 7 thousand such species of weevils, and they belong to at least 11 different lineages of weevils. This does not suggest phylogenetic constraints.
The wide range of this strategy on Earth is perhaps partly owing to the parthenogenetic reproduction documented in some ambrosia beetles.
There is a poor literature on the African species. However, they are indeed present in Africa too.
The widespread distribution, and the fact that fungus-growing has evolved repeatedly in the weevils (family Curculionidae of Coleoptera), show that it is possible for various, unrelated insects to evolve the strategy of fungus-culturing. Why could termites not have done likewise in e.g. Australia?
The fact that, in Australia, at least one species of fungus-growing, wood-consuming weevil has actually converged with termites in the sense of evolving a measure of eusociality indicates that if Australia were suitable for the macrotermitine approach then surely the beetles would have evolved to fill it on this continent if termites could for various reasons not have done so. Nobody is suggesting that weevils could build mounds, but at least there should be more fungus-growing going on in Australia in woody detritus?
It would be interesting to read up some more on ambrosia beetles, to see if any of the 7000 fungus-growing species have their fungus gardens underground – even inside the woody roots.
As an aside, it may also be of note to South African naturalists that
- the Virgilia ‘trees’ falling apart from woodrot in well-known locations, such as Kirstenbosch National Botanic Gardens (https://en.wikipedia.org/wiki/Kirstenbosch_National_Botanical_Garden) and Tsitsikamma National Park (https://en.wikipedia.org/wiki/Tsitsikamma_National_Park), are being consumed - at least in part - by a fungus-growing weevil, alias ‘ambrosia beetles’, and
- each plant possibly has several such beetles (belonging to different genera and perhaps even different subfamilies) at work in it.
One of the species in Virgilia, namely Hapalogenius fuscipennis, is also recorded in Millettia grandis (https://en.wikipedia.org/wiki/Millettia_grandis) elsewhere in South Africa. Millettia tends to replace Virgilia in e.g. Pondoland, but is ecologically similar.
I have long taken note of the fact that these short-lived forest-edge peas (e.g. Virgilia) have such flimsy wood that they collapse and rot promptly after dying. Now I see there’s a new aspect to this soft-wooded strategy; the existence of these fungus-growing weevils in these woods puts a new complexion on the plants.
Hapalogenius sp., a congener of the species found in Virgilia:
http://bdj.pensoft.net//showimg.php?filename=oo_13796.jpg
Scolytoplatypus fasciatus, found in Virgilia:
http://www.boldsystems.org/pics/_w300/CNCCA/CNC_COLEO_00156115%2B1346952548.jpg
http://www.wired.com/2011/07/fungus-farming-beetles/
http://en.wikipedia.org/wiki/Austroplatypus_incompertus
http://en.wikipedia.org/wiki/Ambrosia_beetle
http://www.ncbi.nlm.nih.gov/pubmed/24863476
(writing in progress)
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