Defense against fungus garden parasites in Acro octospinosus

Post here for any notes or records of sightings in the wild. Behaviour, nuptial flights etc, everything about these ants from the Tropics!
Post Reply
User avatar
Acromyrmexbob
Site Admin
Posts: 2199
Joined: Tue Nov 24, 2015 10:32 pm

Defense against fungus garden parasites in Acro octospinosus

Post by Acromyrmexbob » Sun Apr 22, 2018 11:44 pm

Escovopsis is a fungus that wipes out nests of Leaf Cutting ants. It is the worst enemy of the fungus garden which it destroys very quickly once present in the nest. So the workers are very vigilant against this. But the paper below suggests that, contrary to what would be expected, whilst the smallest workers, the minims, tend to the fungus and groom it, keeping it healthy, the bigger workers are most concerned with weeding the fungus. At the early stage of infection, however, minors are more efficient at removing the Escovopsis fungus, whereas once the infection is established, both minors and majors remove the fungus with equal efficiency.

Caste specialization in behavioral defenses against fungus garden
parasites in Acromyrmex octospinosus leaf-cutting ants
D. Abramowski • C. R. Currie • M. Poulsen
Received: 27 April 2010 / Revised: 28 July 2010 / Accepted: 3 August 2010 / Published online: 28 September 2010
International Union for the Study of Social Insects (IUSSI) 2010
Abstract
Division of labor and caste specialization plays
an important role in many aspects of social insect colony
organization, including parasite defense. Within leaf-cutting
ant colonies, worker caste specialization permeates
colony tasks ranging from foraging, substrate incorporation,
brood care, and chemical defenses via glandular secretions
and mutualistic bacteria. Leaf-cutting ants rely on protecting
a mutualistic fungus they grow for food from microfungi
in the genus Escovopsis that parasitizes the ant–fungus relationship.
Here, we examine whether Acromyrmex octospinosus
leaf-cutter ant castes (minors and majors) display task
specialization in two behavioral defenses against Escovopsis:
fungus grooming (the removal of Escovopsis spores)
and weeding (the removal of large pieces of Escovopsisinfected
fungus garden). Using behavioral observations, we
show that minors are the primary caste that performs fungus
grooming, while weeding is almost exclusively performed
by majors. In addition, using a sub-colony infection experimental
setup, we show that at the early stages of infection,
minors more efficiently remove Escovopsis spores from the
fungus garden, thereby restricting Escovopsis spore germination
and growth. At later stages of infection, after
Escovopsis spore germination, we find that major workers
are as efficient as minors in defending the fungus garden,
likely due to the increased importance of weeding. Finally,
we show, using SEM imaging, that the number of sensory
structures is similar between minor and major workers. If
these structures are invoked in recognition of the parasites,
this finding suggests that both castes are able to sense Escovopsis.
Our findings support that leaf-cutter ant behavioral
defense tasks against Escovopsis are subject to caste specialization,
likely facilitated by worker sizes being optimal
for grooming and weeding by minors and majors, respectively,
with important consequences for cultivar defense.

Post Reply