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Taxonomic Classification Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Genus: Allomerus
Species: A. decemarticulatus
General Characteristics:
A. decemarticulatus is a small (workers about 2mm and queens about 5.53mm long) tree-dwelling tropical ant that lives in the rain forests of the northern Amazon in South America and is among the eight species of genus Allomerus. They live inside leaf pouches (domatia) in the tree of only one species Hirtella physophora which is limited to Brazil and French Guiana. Their relationship with their host plant is mutualistic and they also have a symbiotic relationship with fungi only in the order Chaetothyriales creating a rare three-way symbiosis. They're eusocial insects with queens and workers in which they're noticed for their workers' complex and aggressive ambush predatory behavior.
A. decemarticulatus is a small (workers about 2mm and queens about 5.53mm long) tree-dwelling tropical ant that lives in the rain forests of the northern Amazon in South America and is among the eight species of genus Allomerus. They live inside leaf pouches (domatia) in the tree of only one species Hirtella physophora which is limited to Brazil and French Guiana. Their relationship with their host plant is mutualistic and they also have a symbiotic relationship with fungi only in the order Chaetothyriales creating a rare three-way symbiosis. They're eusocial insects with queens and workers in which they're noticed for their workers' complex and aggressive ambush predatory behavior.
Relationship and Behavior with H. physophora and fungi
The tree houses around 1200 workers (per leaf pocket, there are about 40 ants) that protect it from other insects that would eat or harm the tree. The ants have a safe place to live and the plant produces nectar in the leaf pockets to feed the ants. The ants give off carbon dioxide that's absorbed by the pores of the leaf pockets. The ants also give their host nutrients through the domatia and nutrients to the fungus through wastes meanwhile, the fungus gives nutrients to the tree. The fungi grow next to the ants where they can cultivate it and later regurgitate it to use it like glue to make the traps to catch their prey. They build the galleried structures on the stems of the tree using the hairs and fungi for structural support next, they make holes to hide in with their mandibles open ready to attack.
If an insect lands on the branch then the closest ant patrolling the stem will grab a hold of its leg and secrete pheromones to tell the other ants to come help with the prey. They each grab a leg and once they have the prey where they want it, they begin to sting the insect until it dies or is paralyzed and bring it home to share. This way, they're able to take on prey much bigger than themselves since they're taking it down together.
The Research
The Research
Looking at two studies done by Alain Dejean and his collegues, they looked at the tripartite association between A. decemarticulatus, H. physophora and an Ascomycota fungus as well as how they build traps within them. They looked at myrmecotrophy (plants that have a mutualistic association with ants and have domatia or hollowed structures to shelter ants) to see if it could explain the stability of the relationship between the three organisms. Results showed that the more prey captured, the more nutrients given to the host for growth which in turn provides the ants with additional housing and allowed the ants to build longer traps for greater amounts of prey. The carcasses left in the trap then feed the fungus. For the tree, there's a trade off between the partial castration done by the ant workers and myrmecotrophy that indirectly favors plant growth and fitness. Although dependent on the ant's behavior, these mechanisms increased stability of the relationship. Thus, myrmecotrophy, a byproduct benefit for myrmecophytes, may interrupt the stability of myrmecophyte-ant mutualisms because the plant receives a benefit at no cost for the ant.
In the other study, they looked at 34 plants that didn't have leaf pouches so they didn't grow fungus; where 9 raised in a greenhouse without the ants developed leaf pouches but also never bore fungus. When 15 plants were raised with ants then they grew mycelia but after getting rid of ants from 5 of those plants, the fungus on the galleries grew but they were disorganized in structure. Thus, the three organisms have evolved to live with one another and this tree specifically grows leaf pouches for the ants and without the ants, there's no fungus.
They observed how the ants wait and ambush their prey and to kill it, they grab it's legs, antennae, or wings and move in and out of the holes in opposite directions until the prey is stretched out then swarms of worker ants can sting it. The ants move in and out of the holes but in the same direction to move their prey over the top of the gallery and towards the leaf pouch where they can carve it up. This behavior is an example of a collaboration between solitary and cooperative predation. In another study done by Dejean, a single worker could restrain a grasshopper which is equivalent to a 175 lb person holding down a 25,000 lb object moving to escape.
Conclusion:
The symbiosis between these ants with their host plant and the fungi is a complex interaction where the three have evolved to live together. The plants are an example of a myrmecophyte and unlike most mutualisms between ants and fungi, these ants don't receive any nutrients from the fungi. Their predatory behavior has similarly been observed in other ant species, such as symbioses with plants (acacia ants and the bullhorn acacia plant) along with cultivating a fungus (like leaf cutter ants), and ambushing prey (like in the ant species Azteca andreae). But A. decemarticulatus incorporates these advanced behaviors to make a strong device for tricking prey much larger than themselves in which creating a trap as a predatory strategy hasn't been described before in ants
Works Cited
Dejean, Alain et al. "Arboreal Ants Build Traps to Capture Prey." Nature 434.7036 (2005): 973. https://www-nature-com.proxy.lib.iastate.edu/articles/434973a
Dejean, Alain et al. "Predation Success by a Plant-ant Indirectly Favours the Growth and Fitness of Its Host Myrmecophyte." PLoS ONE 8.3 (2013): E59405. http://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC3597600&blobtype=pdf
Wikipedia contributors. "Allomerus decemarticulatus." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 6 Aug. 2018. https://en.wikipedia.org/wiki/Allomerus_decemarticulatus
Image 1- https://en.wikipedia.org/wiki/Allomerus_decemarticulatus
Image 2- https://adlayasanimals.wordpress.com/2013/06/02/allomerus-ant-allomerus-decemarticulatus/
Image 3- http://www.antwiki.org/wiki/Allomerus
Image 4- https://www-nature-com.proxy.lib.iastate.edu/articles/434973a
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