The mutually beneficial interaction
between fungus-growing ants (Hymenoptera: Formicidae: Attini) and their fungi (Agaricales: mostly
Lepiotaceae: Luecocoprineae) is said to have started 45-60 million years ago.
In this symbiotic relationship, the fungus-growing, or attine ants use leaves, flowers,
and detritus as well as dead insects and their feces to mature their fungal
gardens. In addition, they disinfect these added organic materials to protect
the fungi from bacterial infection by licking and chewing them. This also begins
the decomposition process. The
disinfection is attributed to the secretion of antibiotic substance such as phenylacetic
acid, 3-hydroxydecanoic and indoleacetic acid from the ant’s mandibular glands
and metapleaural glands. The thick whitesh granular deposits on the surface of
some of the attine ants are actually actinomycetes-filamentous bacteria, which
also secrete anti-biotic substances. Collectively, these anti-biotic substances
play a big role in suppressing anti-fungal pathogens such as Escovopsis. In return for the protection and gardening,
the fungi produce specialized structures called gongylidia -rich in lipids and
carbohydrates- for the attine ants to consume.
The mutualism between the attine
ants and their cultivars has been conserved for over 45 million years mainly
due to ‘vertical transmission’ of the cultivars. It is referred to as vertical
transmission because attine queen ants carry fungal inocula from their parents
to their new colonies. Lateral transmission of cultivars between colonies has
also been reported and is used to explain incidences when distantly related ant
species cultivate the same fungi or incidences when a single ant species cultivates
distantly related cultivars.
Comparison of free living fungi and
ant-associated fungi has shown similarities between the two. This suggests that
any observed differences between them arose due to domestication of formerly
free living fungi by ants. In relative terms,
recently domesticated fungi show closer links to currently free living fungi,
while fungi domesticated earlier on show closer links to ancient free living
fungi. This data can be explained by co-evolution: fungi cultivated by attine
ants evolved differently than free living fungi. For example, over time, the
cultivated fungi have lost their independent resistance to infection due to the
anti-biotic substances and constant grooming provided by the attine ants. On
the other hand, free living fungi have retained the independent resistance,
likely passed down from ancient species.
Word count: 373
Reference
Currie, C R. “A Community of Ants, Fungi, and Bacteria: a
Multilateral Approach to Studying Symbiosis.” Annual Review of Microbiology 55
(2001): 357–380
I got to see some of these fungal gardens first hand when dealing with Atta in Belize. It was amazing to see how massive some of the colonies and gardens could be. It was nice to learn a bit more about these colonies. I was unaware that the ants saliva was an antibiotic and protected the fungi.
ReplyDelete-Jeff Brown
Mutualistic relationships like this are always so cool to read about, and it's fascinating how organisms have evolved and developed to really be dependent on another organism. In regards to the Attine ants, it sure beats the relationship some ants have with the Ophiocordyceps fungus, which virtually "zombifies" the ant! http://www.scientificamerican.com/article.cfm?id=zombie-ant-fungus-parasite
ReplyDeleteI think the evolved dependence of the fungi on ants is absolutely fascinating. It shows how truly intricate symbiotic relationships are and how closely their evolutionary histories are intertwined. As Jeff mentioned above, I had no idea that the ants' saliva could act as an antibiotic, which makes me wonder if this was evolved so that the ants could farm the fungus, or if it had existed prior to the symbiotic relationship.
ReplyDeleteIt's fascinating to me as it to y'all. I've always thought non-human interactions are simple in nature but obviously that's not true. Even more intriguing is how such mutual relationships start especially because for them to work(based on a human perspective) , involved parties have to make lifestyle changes almost simultaneously. However,I don't think simple organisms can achieve that level of co-ordination and organization and this thought has left me to believe that these interactions are products of chance. And if the evolved interaction offer higher fitness, they get amplified by natural selection.
ReplyDeleteI read your article because we came across this behavior in our insect biology class and I found them to be incredible and interesting. The fact that these ants were basically farming and harvesting their own food, essentially, for the good of the whole colony reminded me that human beings, while we are larger, still have much to learn from these ants who have been doing this for 45 million years! With that, do you know of any agricultural findings that have come from this mutualistic relationship?
ReplyDeleteReading your blog post led me to think about another post that talked about about coral reefs and their symbionts. It would be interesting if someone did a comparative study between these two systems of mutualism to see how similar or different they are/
ReplyDeleteOn a separate note, I actually went on a field trip with Dr. Solomon to collect young queen leafcutter ants that just had their mating flight. During that trip, I actually saw some of that ‘vertical transmission’ which you mentioned in your post. I thought that was a super cool observation and I just wanted to share it with you. :D