Posts Tagged ‘ant’

Surviving the Ant Gut

March 12th, 2011

leaf-cutting-ant-1403Leaf-cutting ants of the genera Acromyrmex and Atta (Family Formicidae: Subfamily Myrmicinae: Tribe Attini) live in mutualistic symbiosis with the basidiomycete Leucocoprinus gongylophorus (Agaricaceae). The ants cultivate the mycobiont mycelium in ‘fungal gardens’ where they brought freshly cut and chew leaves. They apply fecal droplets to the leaf pulp before depositing this mixed substrate to the top of the garden. The fecal fluid contains a large range of hydrolytic enzymes (proteases, pectinases, carbohydrate degrading enzymes) able to efficiently degrade the plant cell wall and cell material. Released carbohydrates serve as a primary source of nutrient for the fungus which then differenciate clusters of a unique tissular structure so-called the ‘gongylidia‘. This massive hyphal swelling are the main food source of the farming leaf-cutting ants. In ant agriculture,the attine ants actively propagate, nurture and defend the basidiomycete cultivar. This mutualistic symbiosis is thought to have originated in the basin of the Amazon rainforest some 50–65 million years ago. The molecular mechanisms driving this ant-fungus mutualism are poorly know.

In their study published in BMC Biology, Schiøtt et al. showed that the pectinolytic enzymes present in the ant fecal droplets are produced by the fungus. The genes encoding the hydrolytic enzymes are  induced in the gongylidia mycelium, ingested by the feeding ants, transported throughout the ant gut before being released in fecal fluids on the top of the fungal garden. It is suggested by the authors that the fungal enzymes evolved to survive the harsh conditions of the ant gut. The on-going sequencing of the genome of Leucocoprinus gongylophorus will undoubtly provide novel insights on the evolution from saprotrophism to this unique mutualistic symbiosis.

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Figure by Schiøtt et al. BMC Biology 2010 8:156   doi:10.1186/1741-7007-8-156

Schiøtt et al. (2010 Leaf-cutting ant fungi produce cell wall degrading pectinase complexes reminiscent of phytopathogenic fungi. BMC Biology 2010, 8:156

Recommended reading: Fungus-Ant mutualism

Photo: © http://www.zsl.org/zsl-london-zoo/animals/inverts/leaf-cutting-ant,59,AN.html

Histoire de Fourmis … suite: Ant Genomes

August 29th, 2010

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Symbioses between plants and fungi, fungi and ants, and ants and plants all play important roles in ecosystems. For those interested by ant ecology and biology, and their interaction with plants, I would recommend reading the paper from Defossez et al. on Ant‐plants and fungi: a new threeway symbiosis‘ published on March 11, 2009 in the New Phytologist. For further ant reading go to the comparative genomics paper published by Bonasio et al. in the 27 August 2010 issue of Science. A collaborative research consortium involving scientists from the US and China report that they have sequenced the genomes of two ant species: Harpegnathos saltator, known as Jerdon’s jumping ant, and the Florida carpenter ant, Camponotus floridanus.

By comparing the genome structure and gene repertoire of the two ant species, and analyzing their transcriptome profiling in different castes, the team obtained clues about gene regulation and epigenetic processes underlying diverse physical and behavioral features in these ant species. They identified up-regulation of telomerase and sirtuin deacetylases in longer-lived H. saltator reproductives, caste-specific expression of microRNAs and SMYD histone methyltransferases, and differential regulation of genes implicated in neuronal function and chemical communication. Their findings provide clues on the molecular differences between castes in ants paving the way for further investigations on everything from brain function and behavior to aging.

Photo: Florida Carpenter Ant (by Alex Wild)

Graveyards on the Move

August 28th, 2010

Cemetery_4Zombie Ants‘, ‘Graveyards on the Move‘ … fungi can make the headlines of newspapers, such as The Guardian, and blog posts (Ancient Zombie Ants, Fungal Parasites & Zombie Ants, Genetics and Behavior, Cordyceps and Nature’s parasitic relationship with it). They referred to the parasitoid Cordyceps fungi (Ascomycota, Pezizomycotina, Sordariomycete, Hypocreales) — a genus that includes about >600 described species. All Cordyceps species are endoparasitoids, mainly on insects and other arthropods.

Jason’s recent tweet  ‘A fun blog post & paper review on Cordyceps entitled “fungal parasites & zombie ants“‘ reminded me one of the more stunning sections of the 2006 BBC’s documentary series Planet Earth showing an ant being preyed on by Cordyceps — you can check out this segment narrated by Sir David Attenborough on YouTube — . Fruiting body of the infecting cordyceps erupting from the ant head and the mushrooming bodies of dead insects are frightening, but so beautiful.

The fungus Ophiocordyceps unilateralis, which is pan-tropical in distribution, causes infected worker ants to leave their nest and die under leaves in the understory of tropical rainforests. Cordyceps spores glue to foraging Carpenter ants (Camponotus leonardi), germinate on the insect cuticule and the fungal hyphae then grows inside the ant body where it releases chemicals that affect host behaviour. Some ants leave the colony and wander off to find fresh leaves on their own, while others fall from their tree-top havens on to leaves nearer the ground. The final stage of the parasitic infection (which may last 3 to 6 days) is the most macabre. In their last hours, infected ants — the zombies — move towards the underside of the leaf they are on and clamp their mandibles in a “death grip” around the central vein, immobilising themselves and locking the fungus in position. Very high densities of dead ants can occur underside of leaves leading to patches. Spores are too large to be wind dispersed and instead fall directly to the ground where they produce secondary spores that infect foraging Carpenter ants as they walk over them.

In a study published last year in PLoS OneMaj-Britt Pontoppidan and her colleagues have shown that the Cordyceps parasitoid not only affects individual ants, but they can also structure the entire host population of a tropical forest in Thailand in terms of its distribution in time and space, and then influence their own distribution: the ‘parasite’s ‘extended phenotype‘. It appeared that the dead ant bodies weren’t randomly distributed in the Thai rainforest floor. Instead they were in large aggregations (the so-called ‘graveyards‘) of up to 26/m2, separated by corpse-free zones. The dead ants had locked onto the undersides of leaves – an example of how the fungus influences its host’s behaviour. The distribution of dead ants appeared to be related to temperature and absolute humidity – things which could influence the survival of fungal spores and thus the chances of an individual ant picking up the infection.

Ant death-grip leaf scars have been documented on 48 Ma fossil leaves, indicating the antiquity of this behaviour (Hughes et al. (2010) Biology Letters online).

Fungal parasites and symbionts play an important role in structuring host plant populations. This study  showed that they also affect animal populations … what about human behavior? (see: the Human Afflicting Strain of Cordyceps Fungus).

BTW, Thanks to its medicinal properties, mushroom hunters in Tibet can earn $900 dollars for an ounce of cordyceps.

Pontoppidan M-B, Himaman W, Hywel-Jones NL, Boomsma JJ, Hughes DP (2009) Graveyards on the Move: The Spatio-Temporal Distribution of Dead Ophiocordyceps-Infected Ants. PLoS ONE 4: e4835. doi:10.1371/journal.pone.0004835

Hughes, DP,  Wappler , T & Lanadeira, CC (2010) Ancient death-grip leaf scars reveal ant-fungal parasitism. Biology Letters. Published online before print August 18, 2010, doi:10.1098/rsbl.2010.0521

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Photo: Cambridge Graveyards, UK © F Martin & A carpenter ant (Camponotus leonardi) whose body has been consumed by the fungus Ophiocordyceps © David P Hughes