defensive behavior

A double defensive mutualism? A case between plants, extrafloral nectaries, and trophobionts

Тhis is the first case reported in the literature of a double defensive mutualism occurring simultaneously on a single plant species.

Guest blog post by Cássio Pereira

The Zeyheria montana shrub is quite common in the Brazilian Cerrado and is known to have extrafloral nectaries on the leaf blade that attract patrolling ants such as the aggressive Ectatomma tuberculatum. The ant, in turn, defends the leaves against the action of herbivores. However, extrafloral nectaries can distract ants on the leaves, segregating them from the reproductive parts and preventing them from driving away pollinators, which can benefit the action of florivores and nectar robbers.

Individual of *Zeyheria montana* on rocky outcrops in Minas Gerais, southeastern Brazil.

Surprisingly, in southeastern Brazil, we observed a second defensive mutualism occurring on the reproductive tissues of these shrubs between E. tuberculatum and the treehopper Guayaquila xiphias, which provides the ant with honeydew in exchange for protection. This trophobiosis relationship (interaction between ants and phytophagous hemipterans that secrete sugary exudates) seems to be effective not only in the defense of floral buds and flowers, but also of the fruit, which, despite being dry, contains a lot of water in its formation and is attacked by beetles of the Curculionidae family.

The treehoppers *G. xiphias* at the base of *Z. montana* fruits.

As far as we know, this is the first case reported in the literature of a double defensive mutualism occurring simultaneously on a single plant species. Given this record, important questions arise regarding these interactions. Is the trophobiosis that occurs in reproductive organs capable of increasing the fitness of these plants? Although these ants are probably also scaring away possible pollinating insects, could the fact that Z. montana is primarily pollinated by hummingbirds offset this loss given that hummingbirds are larger and perhaps immune to ant attacks?

Reaction of the aggressive *E. tuberculatum* ant, which protects the treehoppers from attacking invaders.

Our record raises more questions than it answers. Long-term Z. montana population studies would help improve our ecological understanding of these interactions.

A hair’s breadth away: New tarantula species and genus honors Gabriel García Márquez

With its extraordinary defensive hairs, a Colombian tarantula proved itself as not only a new species, but also a new genus. It is hypothesised that the new spider is the first in its subfamily to use its stinging hairs in direct attack instead of ‘kicking’ them into the enemy.

Described in the open access journal ZooKeys by an international research team, led by Carlos Perafán, University of the Republic, Uruguay, the name of the new spider genus honours an indigenous people from the Caribbean coast region, whose language and culture are, unfortunately, at serious risk of extinction. Meanwhile, its species’ name pays tribute to renowned Colombian author and Nobel laureate for his novel ‘One Hundred Years of Solitude’ Gabriel García Márquez.

The new tarantula, formally called Kankuamo marquezi, was discovered in Sierra Nevada de Santa Marta, Colombia. When examined, the arachnid showed something extraordinary about its defensive hairs and its genitalia. The hairs were noted to form a small oval patch of lance-shaped barbs, hypothesised by the scientists to have evolved to defend their owners by direct contact.

On the other hand, when defending against their aggressors, the rest of the tarantulas in this subfamily need to first face the offender and then vigorously rub their hind legs against their stomachs. Aimed and shot at the enemy, a ball of stinging hairs can cause fatal injuries to small mammals when landed into their mucous membrane (the layer that covers the cavities and shrouds the internal organs in the body). Once thrown, the hairs leave a bald spot on the tarantula’s belly.

“This new finding is a great contribution to the knowledge of the arachnids in Colombia and a sign of how much remains to be discovered,” point out he authors.

“The morphological characteristics present on Kankuamo marquezi open the discussion about the phylogenetics relationship between subfamilies of Theraphosidae tarantulas and the evolutionary pressures that gave rise to the urticating hairs.”

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Original source:

Perafán C, Galvis W, Gutiérrez M, Pérez-Miles F (2016) Kankuamo, a new theraphosid genus from Colombia (Araneae, Mygalomorphae), with a new type of urticating setae and divergent male genitalia. ZooKeys 601: 89-109. doi: 10.3897/zookeys.601.7704

Call for arms and stings: Social wasps use alarm pheromones to coordinate their attacks

Humans might know them as vicious stingers, but yellow jacket wasps also impress with their vigorous protection over their young. To resolve the mystery around their complex defensive behavior, a Canadian research team, led by Dr. Sean McCann, Simon Fraser University, have used simple components to develop and construct a device that consequently helped them to locate the species-specific alarm pheromones in three wasp groups. The insects use the emission of these substances to mark the enemy threatening their colonies and then join forces against it. The study is published in the open-access Journal of Hymenoptera Research.

Social insects invest a lot of work and resources in their colonies, working together to raise large numbers of larvae. Because their nests contain so many protein-rich, yet helpless young, they have evolved elaborate defence mechanisms to protect them.

One way the social wasps have found to increase the efficiency of their defence is through chemical signals, called alarm pheromones, which are used to rouse the colony to action and mark intruders for attack. As a result, the coordinated attack of a large colony of yellow jackets can drive even large predators away from the nest. Several social wasp alarm pheromones have been discovered, and most of these have been detected in the venom sacs of the wasps. Nonetheless, the process of finding out which chemicals are involved requires many experiments in the field in addition to chemical analysis.

“We developed a new and standardized method to evaluate alarm pheromone activity in yellowjackets and other social wasps that is inexpensive and easy to use. The device we constructed uses off-the-shelf components, and consists of a pair of black targets enclosing a pair of microphones,” explain the authors.

“A test substance and a control can be applied to each target, and then a stereo audio file is recorded at the nest site,” they further comment. “When wasps hit the black targets, it makes a percussive sound, almost like a drum. The resulting stereo file is then split and analysed with an open-source software program to count the number of strikes received by the treatment and control targets.”

The advantage of this system is its ease of use, low cost, and the ability to use rapid automated counting, which saves a lot of time compared to other methods.

The scientist have used this new method to figure whether three species of yellow jackets (the western yellow jacket, the common yellow jacket and the German yellow jacket) have alarm pheromones, and whether each species is able to recognize each of the alarm pheromones of the rest.

“We found evidence for alarm pheromones in all three species, and that each species recognizes and responds to the other species’ alarm pheromones in similar ways,” say the researchers. “We conclude that the chemical messages produced by these three yellow jacket species must be very similar.”

“It makes sense that wasps can recognize the alarm pheromones of other species, because it would be advantageous to be able to detect a pheromone-marked predator that has attacked other wasps nearby and start stinging it to drive it away before it finds their own colony,” conclude the authors.

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Original source:

McCann S, Moeri O, Jimenez SI, Scott C, Gries G (2015) Developing a paired-target apparatus for quantitative testing of nest defense behavior by vespine wasps in response to con- or heterospecific nest defense pheromones. Journal of Hymenoptera Research 46: 151-163. doi: 10.3897/JHR.46.6585.