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New species of spider wasp may use chemical signals from dead ants to protect nest

A new species of spider wasp, the ‘Bone-house Wasp,’ may use chemical cues from dead ants as a nest protection strategy, according to a recent study published July 2, 2014 in the open-access journal PLOS ONE by Michael Staab from University of Freiburg, Germany, and his colleagues from China and Germany.

Wasps use a wide variety of nest protection strategies, including digging holes or occupying pre-existing cavities such as in wood. Previous studies showed that the nests of cavity-nesting wasps contain several brood cells separated by thin walls of plant debris, resin, or soil. Once the females have finished constructing the nest, laying eggs, and providing food, they construct an outermost vestibular cell to close the nest. After construction, female wasps abandon the brood and do not care for their offspring anymore. Nest protection strategies play a central role in brood survival, and in this study, scientists interested in better understanding these strategies collected ~800 nests of cavity-nesting wasps with ~1900 brood cells belonging to 18 species in South-East China.

The scientists found a nesting behavior previously unknown in the entire animal kingdom: in over 70 nests they found an outer vestibular cell filled with dead ants. The species constructing these ant-filled vestibular cell was so far unknown to science and was described in the same study as the ‘Bone-house Wasp’ (Deuteragenia ossarium), after graveyard bone-houses or ossuaries. The scientists also found lower parasitism rates in “Bone-house” nests than in nests of similar cavity-nesting wasps. The authors suggest that D. ossarium nests are less vulnerable to natural enemies, potentially supporting the outer cell’s role in defense, which most likely involves chemical cues emanating from the dead ants used as nest-building material.

Dr. Staab added, “Our discovery demonstrates in an impressive way, what fascinating strategies of offspring-protection have evolved in the animal kingdom.”

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The above story is based on materials provided by PLOS. Note: Materials may be edited for content and length.

Agriculture and Food News — ScienceDaily

Ants protect acacia plants against pathogens

Jan. 15, 2014 — The biological term “symbiosis” refers to what economists and politicians usually call a win-win situation: a relationship between two partners which is beneficial to both. The mutualistic association between acacia plants and the ants that live on them is an excellent example: The plants provide food and accommodation in the form of food bodies and nectar as well as hollow thorns which can be used as nests. The ants return this favor by protecting the plants against herbivores. Researchers at the Max Planck Institute for Chemical Ecology in Jena, Germany, have now found that ants also keep harmful leaf pathogens in check. The presence of ants greatly reduces bacterial abundance on surfaces of leaves and has a visibly positive effect on plant health. Study results indicate that symbiotic bacteria colonizing the ants inhibit pathogen growth on the leaves.

Myrmecophytes are plants which live in a symbiotic relationship with ants. The acacia species Acacia hindsii, which is native to tropical dry forests in Central America, is such a myrmecophyte. Its inhabitants are ants of the genus Pseudomyrmex. The ants depend completely on their host plants for nectar and the food bodies rich in proteins and lipids which they require. The acacia also provides shelter, the so-called domatia, in the hollows of its swollen thorns. In return for room and board, mutualistic Pseudomyrmex ferrugineus ants become bodyguards, protecting their host against herbivores and competing plants. However, some ants also benefit from the plant’s services without giving anything in return, such as the parasitic ant species Pseudomyrmex gracilis.

Scientists at the Max Planck Institute for Chemical Ecology have now looked more deeply into the insect-plant interaction, asking whether the tiny bodyguards also provide protection against microbial pathogens. They compared the leaves of acacia plants which were inhabited by either mutualistic or parasitic ants to leaves from which ants had been removed. Intriguingly, the leaves of acacia colonized by parasitic ants showed more leaf damage from herbivores and microbial pathogens than did the leaves that had mutualistic ants. The presence of the right symbiotic partner seemed to have a positive effect on the plant’s health.

Analysis of the surfaces of the leaves revealed that the number of plant pathogens as well as of necrotic plant tissues increased considerably when mutualistic Pseudomyrmex ferrugineus ants were absent. These plants also showed strong immune responses in the form of an increased concentration of salicylic acid, a plant hormone which regulates defense against pathogens. Detailed analysis of the bacterial composition on the surfaces of the leaves suggested that the presence of mutualistic ants changed the bacterial populations and reduced harmful pathogens. Although far less pronounced, this effect could also be observed in parasitic ants.

How antimicrobial protection is transferred from ants to plant is still unclear. Chilean researcher Marcia González-Teuber, first author of the publication, suspected that microorganisms associated with the ants might play a role. Because acacia leaves are touched mainly by ants’ legs, she extracted the legs of mutualistic and parasitic ants and tested the effect of the extracts on the growth of bacterial pathogens in the lab. Plant pathogen Pseudomonas syringae was sensitive to the application of leg extracts of both ant species and its growth was inhibited. In the next step, the scientist isolated and identified bacteria from the legs of the ants. In lab tests, bacterial strains of the genera Bacillus, Lactococcus, Pantoea and Burkholderia effectively inhibited the growth of Pseudomonas bacteria isolated from infected acacia leaves. Interestingly, some of the bacterial genera associated with the ants are known to produce antibiotic substances.

The Jena researchers have thus added another level of interaction to the symbiosis between ants and their host plants. “Such mutualistic relationships are much more complex than previously thought. In the future, we will have to include bacteria and other microorganisms in our considerations,” says Wilhelm Boland, head of the Department of Bioorganic Chemistry at the Max Planck Institute. Studies on symbiotic relationships between ants and myrmecophytic plants should not overlook the role of bacterial partners that help the ants protect “their” plants.

ScienceDaily: Agriculture and Food News

Ants turn unwelcome lodgers into a useful standing army

Sep. 9, 2013 — Mercenary soldiers are notoriously unreliable because their loyalty is as thin as the banknotes they get paid, and they may turn against their employers before moving on to the next dirty job. Not so in fungus-farming ants, where a new study reports that permanent parasites that are normally a chronic social burden protect their hosts against a greater evil.

“Our experiments show that the scouts can detect whether or not a host colony has a cohabiting guest ant colony before deciding to initiate a raid so the guest ants serve as an effective front line defense.

Dr. Rachelle Adams

Ants are unusually free of infectious diseases but their societies are often invaded by social parasites; insects that exploit the resources of ant colonies for their own benefit. Many such social parasites escape detection by the social immune system of their hosts by producing bar-code like chemical recognition labels similar to the host’s own. Others use brute force or obnoxious chemicals to infiltrate or usurp host colonies. One particularly devious ant genus, Megalomyrmex, produces alkaloid-based venoms to repel and poison their host’s and adversaries.

This week in PNAS, researchers from the Centre for Social Evolution at the Department of Biology, University of Copenhagen report a surprising story of ant warfare between three parties, reminiscent of dramas in human history and literature: The victims are peaceful fungus-farming ants that by a remarkable strike of evolutionary misfortune have two other ants as natural enemies.

Ghengis Khan hordes coming

One is an agile raider whose scouts are always on the lookout for new farmer-colonies and recruit their nestmate warriors for swift strikes. They kill or chase away the defenders and pillage and plunder brood and the farmers’ crop to move on after some days in search of a new colony to usurp — not unlike the hordes of Ghengis Khan that laid waste to Asian and European settlements in the middle ages.

However, the fungus-farming ants have powerful protectors. Paradoxically, these are the second natural ant enemy of the farmers, a highly specialized Megalomyrmexspecies that uses its alkaloid poison to permanently move in with a farming host colony to exploit its fungus farm at relative leisure. Lodging of these unwelcome guest ants is a lifelong burden for the farmers, but they do survive and realize some reproductive success. However, having a colony of guest ant lodgers turns out to be a life-saving asset when mobile raiders threaten them, as the guest ants rise to the defense of their hosts.

Using laboratory experiments, the authors show that the guest ant defenses are so effective that they not only kill raiders, but their mere presence greatly decreases the probability of a raid.

Scouts can detect

Our experiments show that the scouts can detect whether or not a host colony has a cohabiting guest ant colony before deciding to initiate a raid so the guest ants serve as an effective front line defense, explains Dr. Rachelle Adams, the lead author of the study.

The scientists directly observed how mass recruitment behavior by the guest ants works and captured it on video (http://www.megalomyrmex.com/Videos.html).

When a Megalomyrmex worker discovered an invading raider, she quickly returned to the cavity to excite her sister workers, and one by one they came out, soon overpowering the invaders, so a raid was prevented, says Dr. Adams.

The results of the study help explain why the guest ant parasite is common in the Panamanian sites where the colonies were collected, a very unusual situation as socially parasitic ants are normally very rare.

The study illustrates how sophisticated and subtle co-evolutionary processes driven by natural selection can be. The results not only show that the idea that “the enemy of my enemy is my friend” can work in the world of ants, but also that natural selection can maintain lesser evils when that helps prevent greater harm, similar to the well-known example of sickle-cell anemia being maintained in areas where potentially deadly malaria is endemic, but not elsewhere.

These kinds of interaction, where being a foe or friend depends on a the presence of a third party, are probably far more common than we realize, and may be fundamental for the coevolution of interacting species, adds Dr. David R. Nash, the senior corresponding author of the study.

ScienceDaily: Agriculture and Food News

Sanction mechanism identified between ants and host plants

July 16, 2013 — In nature, many forms of plant-animal mutualism exist in which each partner benefits from the presence of the other. Although mutualistic interactions offer advantages for both partners, they are nonetheless a source of conflict. CNRS researchers from Toulouse III University — Paul Sabatier and the IRD have recently observed an original sanction interaction between a plant and an ant. In French Guiana, the Hirtella physophora plant is capable of retaliating against the “guest ants” that prevent it from flowering. These results illustrate the importance of sanction mechanisms, which prevent a mutualistic partner from becoming a parasite.

This work was published in Evolutionary Biology on 12 July 2013.

In the forests of French Guiana, Allomerus decemarticulatus ants and the undergrowth plant Hirtella physophora are closely associated. The ants live in the leaf pockets of the plant, where they protect it from plant-eating insects. This “win-win” arrangement is an example of mutualism, since each partner benefits from the presence of the other. But even good relationships can turn sour. The ants sometimes cheat and destroy more than two-thirds of the flower buds of their host plant in order to influence the growth-reproduction balance.

Experiments reproducing the destruction of buds by ants have shown that plants whose buds have been destroyed grow more quickly than others. This explains the ants’ behavior — by preventing the plants from producing flowers, the ants force them to channel their energy into leaf production, which means more leaf pockets. But the plant has a defense mechanism. If too many buds are destroyed, the leaf pockets it produces are particularly small, so that the ants are unable to use many of them. The host plants are therefore able to sanction their guests when they become too virulent.

This study, carried out by CNRS researchers of Toulouse III University — Paul Sabatier and the IRD (1) show empirically, and for the first time that in the relationship between a plant and an insect, sanction mechanisms can be used to maintain mutualism and prevent the relationship from becoming unilateral exploitation.

1) Laboratories involved: Evolution et diversité biologique (EDB) (CNRS/Université Toulouse III- Paul Sabatier/ENFA) ; Ecologie des forêts de Guyane (ECOFOG) (CNRS/AgroParisTech/INRA/CIRAD/Université des Antilles et de la Guyane); Laboratoire d’écologie fonctionnelle et environnement (ECOLAB) (CNRS/ Université Toulouse III- Paul Sabatier/INP-ENSAT), Laboratoire Botanique et bioinformatique de l’architecture des plantes (AMAP) (CNRS/INRA/CIRAD/Université Montpellier 2/IRD) and Laboratoire Maladies Infectieuses et Vecteurs : Écologie, Génétique, Évolution et Contrôle (MIVEGEC) (Université Montpellier 1/Université Montpellier 2/IRD/CNRS).

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Story Source:

The above story is reprinted from materials provided by CNRS (Délégation Paris Michel-Ange).

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. Pierre-Jean G. Malé, Jean-Baptiste Ferdy, Céline Leroy, Olivier Roux, Jérémie Lauth, Arthur Avilez, Alain Dejean, Angélique Quilichini, Jérôme Orivel. Retaliation in Response to Castration Promotes a Low Level of Virulence in an Ant–Plant Mutualism. Evolutionary Biology, 2013; DOI: 10.1007/s11692-013-9242-7

Note: If no author is given, the source is cited instead.

ScienceDaily: Agriculture and Food News