Weeding Behavior
If you have ever gardened before, you understand the importance of getting rid of those pesky weeds. When taking care of these fungal gardens, ants also face a similar dilemma. More often than not, other fungi and microorganisms are attracted to these nutrient-rich fungal gardens. Weeding behaviors have developed as a way for the ants to select for their fungal cultivar and get rid of any unwanted organisms.
Weeding is done by the ants using their mandibles to remove unwanted debris from the fungal cultivar. The ants remove dead fungal debris, fungal spores, and fungal pathogens and move them to a spot away from their gardens designated for waste (1, 2). These waste areas allow the ants to isolate the pathogens and prevent them from further contaminating their fungal garden.
Nilsson-Møller, S., Poulsen, M., & Innocent, T. M. (2018). A Visual Guide for Studying Behavioral Defenses to Pathogen Attacks in Leaf-Cutting Ants. JoVE, 140, e58420. https://doi.org/10.3791/58420
Aylward, F. O., Currie, C. R., & Suen, G. (2012). The Evolutionary Innovation of Nutritional Symbioses in Leaf-Cutter Ants. Insects, 3(1), 41–61. https://doi.org/10.3390/insects3010041
Additionally, in a study run by Katie Kyle (a graduate student in the Klassen Lab at the University of Connecticut), it has been demonstrated that Trachymyrmex septentrionalis ants respond to peptaibols, which are secondary metabolites produced by pathogenic Trichoderma fungi (3). This means that these ants are able to chemically sense the peptaibols produced by these pathogens and respond by increasing their hygienic behaviors, such as weeding, to prevent infection.
Kyle, K. E., Puckett, S. P., Mauricio, A., Samples, R. M., Earp, C. E., Raja, H. A., Pearce, C. J., Ernst, M., J., J. J., Adams, M. E., Oberlies, N. H., Dorrestein, P. C., Klassen, J. L., & Balunas, M. J. (2023). Trachymyrmex septentrionalis ants promote fungus garden hygiene using Trichoderma-derived metabolite cues. Proceedings of the National Academy of Sciences, 120(25), e2219373120. https://doi.org/10.1073/pnas.2219373120
Nilsson-Møller et al., 2018
Video of weeding behavior in Acromyrmex echinatior ants
Trash
Trash
Food
ant colony
Images from the Klassen lab of Atta texana (left) and Trachymyrmex septentrionalis (right) ant designated waste areas
Grooming Behavior
Ants participate in grooming behaviors to essentially "wash" fungal spores off of certain surfaces. They groom themselves, each other, and their fungal cultivar. Grooming can occur differently depending on what the ants are cleaning.
​
-
Self-grooming
-
ants will first clean off their antennae using specialized antennae cleaners that are attached to their front legs​
-
these antennae cleaners are made up of tiny bristles and comb-like structures to help scrape off small particles, such as pathogenic fungal spores
-
-
the ant will then clean off their legs (including the antennae cleaners) using their tongues (1)
-
​
-
Allogrooming​
-
ants will help to groom and clean one another
-
they groom with their tongues, licking each other clean
-
allogrooming also functions as a social behavior
-
​
-
Fungus grooming
-
ants lick the fungus to help remove pathogenic spores and other unwanted microorganisms​
-
​
Ants mainly rely on their tongues for cleaning and storing spores/debris in a specialized cavity known as the infrabuccal pocket. The contents of the infrabuccal pocket get emptied into waste areas for disposal (4).
Nilsson-Møller, S., Poulsen, M., & Innocent, T. M. (2018). A Visual Guide for Studying Behavioral Defenses to Pathogen Attacks in Leaf-Cutting Ants. JoVE, 140, e58420. https://doi.org/10.3791/58420
Little, A. E. F., Murakami, T., Mueller, U. G., & Currie, C. R. (2003). The infrabuccal pellet piles of fungus-growing ants. Naturwissenschaften, 90(12), 558–562. https://doi.org/10.1007/s00114-003-0480-x
Nilsson-Møller et al., 2018
Video of self grooming behavior
Fecal Droplets
One important factor when growing crops is to give them the proper nutrients to help them grow, which can be done with the help of fertilizer. Ants have their own type of fertilizer: fecal droplets. Ants apply fecal droplets directly to their fungal gardens to promote growth. These fecal droplets contain recycled fungal enzymes from their food, which help to break down plant material (5, 6).
Hölldobler, B., & Wilson, E. O. (2010). The Leafcutter Ants: Civilization by Instinct. W. W. Norton & Company.
​
Rønhede, S., Boomsma, J. J., & Rosendahl, S. (2004). Fungal enzymes transferred by leaf-cutting ants in their fungus gardens. Mycological Research, 108(1), 101–106. https://doi.org/10.1017/S0953756203008931
While these fecal droplets promote cultivar growth, they do not appear to stop pathogens from invading (7). When grooming the fungus gardens, ants also add chemical secretions from their metapleural glands. These chemicals act as antimicrobial agents and help to decrease pathogenic spore development (8).
Fernández-Marín, H., Nash, D. R., Higginbotham, S., Estrada, C., van Zweden, J. S., d'Ettorre, P., Wcislo, W. T., & Boomsma, J. J. (2015). Functional role of phenylacetic acid from metapleural gland secretions in controlling fungal pathogens in evolutionarily derived leaf-cutting ants. Proceedings. Biological sciences, 282(1807), 20150212. https://doi.org/10.1098/rspb.2015.0212
Rodrigues, A., Carletti, C. D., Bueno, O. C., & Pagnocca, F. C. (2008). Leaf-cutting ant faecal fluid and mandibular gland secretion: Effects on microfungi spore germination. Brazilian Journal of Microbiology, 39, 64–67. https://doi.org/10.1590/S1517-83822008000100016
De Fine Licht et al., 2013
Antibiotics
Leafcutter ants use antibiotics to help ward off pathogens and keep their gardens free from any undesired microorganisms. The ant-cultivar-pathogen symbiosis becomes even more complex when you factor in Pseudonocardia, a type of Actinobacteria with antibiotic properties. The symbiosis between ants and Pseudonocardia arose early on in fungus-farming ant evolution and has been repeatedly lost and regained throughout many lineages (9).
Pseudonocardia is beneficial for the ants because they provide secondary metabolites that defend against other microorganisms, including Escovopsis. However,
since Escovopsis is in an evolutionary arms race with the ants, Pseudonocardia has evolved mechanisms to prevent antibiotic resistance. To maintain genetic diversity and avoid resistance, they are able to undergo horizontal gene exchange within secondary metabolite biosynthetic gene clusters (10).
Li, H., Horn, H. A., Pupo, M. T., Clardy, J., Rabeling, C., Schultz, T. R., & Currie, C. R. (2018). Convergent evolution of complex structures for ant–bacterial defensive symbiosis in fungus-farming ants. Proceedings of the National Academy of Sciences, 115(42), 10720-10725. https://doi.org/10.1073/pnas.1809332115
Li et al., 2018
Attine fungus-growing ant phylogeny. Black dots represent presence of Pseudonocardia while white dots represent their absence
Goldstein, S. L., & Klassen, J. L. (2020). Pseudonocardia Symbionts of Fungus-Growing Ants and the Evolution of Defensive Secondary Metabolism. Frontiers in Microbiology, 11, e621041. https://doi.org/10.3389/fmicb.2020.621041
Holmes et al., 2016
Picture of Pseudonocardia (white) on top of an Acromyrmex echinatior ant (left) along with microscopic images (right)
Literature Cited
1. Nilsson-Møller, S., Poulsen, M., & Innocent, T. M. (2018). A Visual Guide for Studying Behavioral Defenses to
Pathogen Attacks in Leaf-Cutting Ants. JoVE, 140, e58420. https://doi.org/10.3791/58420
2. Aylward, F. O., Currie, C. R., & Suen, G. (2012). The Evolutionary Innovation of Nutritional Symbioses in Leaf-
Cutter Ants. Insects, 3(1), 41–61. https://doi.org/10.3390/insects3010041
​
3. Kyle, K. E., Puckett, S. P., Mauricio, A., Samples, R. M., Earp, C. E., Raja, H. A., Pearce, C. J., Ernst, M., J., J. J.,
Adams, M. E., Oberlies, N. H., Dorrestein, P. C., Klassen, J. L., & Balunas, M. J. (2023). Trachymyrmex septentrionalis ants promote fungus garden hygiene using Trichoderma-derived metabolite cues. Proceedings of the National Academy of Sciences, 120(25), e2219373120. https://doi.org/10.1073/pnas.2219373120
​
4. Little, A. E. F., Murakami, T., Mueller, U. G., & Currie, C. R. (2003). The infrabuccal pellet piles of fungus-
growing ants. Naturwissenschaften, 90(12), 558–562. https://doi.org/10.1007/s00114-003-0480-x
​
5. Hölldobler, B., & Wilson, E. O. (2010). The Leafcutter Ants: Civilization by Instinct. W. W. Norton & Company.
​
6. Rønhede, S., Boomsma, J. J., & Rosendahl, S. (2004). Fungal enzymes transferred by leaf-cutting ants in their
fungus gardens. Mycological Research, 108(1), 101–106. https://doi.org/10.1017/S0953756203008931
​
7. Rodrigues, A., Carletti, C. D., Bueno, O. C., & Pagnocca, F. C. (2008). Leaf-cutting ant faecal fluid and mandibular
gland secretion: Effects on microfungi spore germination. Brazilian Journal of Microbiology, 39, 64–67. https://doi.org/10.1590/S1517-83822008000100016
8. Fernández-Marín, H., Nash, D. R., Higginbotham, S., Estrada, C., van Zweden, J. S., d'Ettorre, P., Wcislo, W. T., &
Boomsma, J. J. (2015). Functional role of phenylacetic acid from metapleural gland secretions in controlling fungal pathogens in evolutionarily derived leaf-cutting ants. Proceedings. Biological sciences, 282(1807), 20150212. https://doi.org/10.1098/rspb.2015.0212
​
9. Li, H., Horn, H. A., Pupo, M. T., Clardy, J., Rabeling, C., Schultz, T. R., & Currie, C. R. (2018). Convergent
evolution of complex structures for ant–bacterial defensive symbiosis in fungus-farming ants. Proceedings of the National Academy of Sciences, 115(42), 10720-10725. https://doi.org/10.1073/pnas.1809332115
​
10. Goldstein, S. L., & Klassen, J. L. (2020). Pseudonocardia Symbionts of Fungus-Growing Ants and the Evolution
of Defensive Secondary Metabolism. Frontiers in Microbiology, 11, e621041. https://doi.org/10.3389/fmicb.2020.621041
Photos
1. Nilsson-Møller, S., Poulsen, M., & Innocent, T. M. (2018). A Visual Guide for Studying Behavioral Defenses to
Pathogen Attacks in Leaf-Cutting Ants. JoVE, 140, e58420. https://doi.org/10.3791/58420
​
2. De Fine Licht, H. H., Schiøtt, M., Rogowska-Wrzesinska, A., Nygaard, S., Roepstorff, P., & Boomsma, J. J. (2013).
Laccase detoxification mediates the nutritional alliance between leaf-cutting ants and fungus-garden symbionts. Proceedings of the National Academy of Sciences, 110(2), 583–587. https://doi.org/10.1073/pnas.1212709110
​
3. Li, H., Horn, H. A., Pupo, M. T., Clardy, J., Rabeling, C., Schultz, T. R., & Currie, C. R. (2018). Convergent
evolution of complex structures for ant–bacterial defensive symbiosis in fungus-farming ants. Proceedings of the National Academy of Sciences, 115(42), 10720-10725. https://doi.org/10.1073/pnas.1809332115
​
4. Holmes, N. A., Innocent, T. M., Heine, D., Bassam, M. A., Worsley, S. F., Trottmann, F., Patrick, E. H., Yu, D. W.,
Murrell, J. C., Schiøtt, M., Wilkinson, B., Boomsma, J. J., & Hutchings, M. I. (2016). Genome Analysis of Two Pseudonocardia Phylotypes Associated with Acromyrmex Leafcutter Ants Reveals Their Biosynthetic Potential. Frontiers in Microbiology, 7. e235901. https://www.frontiersin.org/articles/10.3389/fmicb.2016.02073