A blog post highlighting the article by  P. M. Kietzman, P. K. Visscher, J. K. Lalor in Insectes Sociaux

By Parry Macdonald Kietzman

The remarkable system of communication used by honey bees to coordinate their daily activities is well known, though most people are primarily aware of the waggle dance. This positive feedback signal is one that communicates the distance and direction of some item of interest, most commonly a food source, to a worker bee’s nestmates. Perhaps less well-known is the stop signal, an acoustic negative feedback signal that can be used as a counter to the waggle dance, inhibiting recruitment and decreasing foraging (reviewed in Kietzman and Visscher 2015).

One use of the stop signal occurs when foragers encounter danger, such as an attack from other bees or a predator, at a food source (Nieh 2010). Nieh (2010) simulated such attacks at a feeding station by pinching foragers’ legs with forceps. Back at the hive, these foragers were then much more likely to use the stop signal on other bees advertising that same location with the waggle dance than they were on dancers advertising other food sources.

Our experiment was originally intended as a pilot study with the goal of practicing a method similar to Nieh’s (2010) technique of pinching bees’ hind femurs during their visits to a feeding station so that we could then use that technique in a later study. We established a colony of bees in a two-frame observation hive (1/4 or 1/5 a regular-sized hive with observation windows on the sides) on the premises of the University of California, Riverside’s Agricultural Operations. We trained the bees to visit a feeding station baited with sugar water 100m away from the hive, and an observer there gently caught visiting foragers in a small net and marked them on the thorax with one of two colors of paint pen depending on which treatment they received.

Using a coin toss to help randomize the treatments, approximately half the visiting foragers were “attacked” with a pinch to the hind femur and the other half were not. I watched the marked bees’ waggle dances back at the hive and recorded them using an HD video camera. A detailed analysis of the video recordings revealed that bees that had not been pinched at the feeder performed significantly more and longer waggle dances than the bees that had been pinched. Additionally, the pinched bees produced significantly more stop signals upon their return to the hive than the unpinched bees.

These results were very much in line with what we expected based on Nieh’s (2010) findings, however, we also made the surprising observation that most of the stop signals we recorded—about 70%–were performed by unmarked bees that had probably never visited the feeding station at all.

Though we don’t have a definitive answer for why so many unmarked bees used the stop signal on dancers advertising the feeding station, there are a few possible explanations. One is that the unmarked bees may have been foraging at another location and were not promptly unloaded upon their return to the hive because the unloader bees were overwhelmed by the influx of food coming from the feeding station. Stop signaling has often been found to increase when the bees have access to a feeding station (reviewed in Kietzman and Visscher 2015), and most of this stop signaling is produced by tremble dancers. Foragers perform the tremble dance when they are not unloaded quickly (Seeley 1992), so if there were insufficient unloader bees available due to the large amount of food coming from the feeding station then this could account for the stop signaling performed by unmarked bees.

A second explanation is that the stop signalers could have been unloader bees rather than foragers, and that these bees were using the stop signal in an attempt to decrease what had become an unmanageable number of foragers exploiting the feeding station. This use of the stop signal, while plausible, has not yet been measured and would likely be an interesting and productive area of study.

Finally, a rich, unlimited source of food such as a feeding station can readily be compared to hive robbing rather than typical foraging on flowers. Johnson and Nieh (2010) modeled a robbing event and showed that the stop signal could successfully be used to quickly shut it down, which would be beneficial if the robbed hive were very strong and an excessive number of robbing foragers were being killed. It is possible that the pinched bees from our experiment were emitting alarm pheromone (signaling a threat to the other bees), and that other bees in the colony interpreted this as evidence that they had been present during a robbing situation. If this were the case, the stop signaling we observed could have been an attempt to shut down what was perceived as an unfavorable robbing event.

Clearly, we have yet to decipher all the meanings of what is a versatile and effective communication signal.

 

References

Johnson, BR and Nieh, JC. 2010. Modeling the adaptive role of negative signaling in honey bee intraspecific competition. Journal of Insect Behavior 23: 459-471.

Kietzman, PM and Visscher, PK. 2015. The anti-waggle dance: use of the stop signal as negative feedback. Frontiers in Ecology and Evolution 3: 54-58.

Nieh, JC. 2010. A negative feedback signal that is triggered by peril curbs honey bee recruitment. Current Biology 20: 310-315.

Seeley, TD. 1992. The tremble dance of the honey bee: messages and meanings. Behavioral Ecology and Sociobiology 31: 375-383.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1: observing waggle dances and stop signals.

A blog post highlighting the article by M.F. Torres and A. Sanchez in Insectes Sociaux

By María Fernanda Torres

Perhaps one of the most astonishing features of ants is their ability to establish mutualistic associations with plants, myrmecophyte plants in particular. About 110 ant species nest exclusively inside hollow structures in leaves, stems or roots the host plant produces (Chomicki and Renner 2015). The mutualism is beneficial for the ants because the host plant provides the colony with housing and food. This food can be obtained directly from the plant or honeydew secreted from the ant-tended hemipterans living on the plant. For the plant, hosting an ant colony is comparable to having its own defense army for a lower cost than producing extensive chemical defenses.

For both members of a mutualism, identifying and locating (or attracting) the right partner is a crucial step in the establishment of the mutualism. Fertile founding queens (alates) emerge from the colony and, after the nuptial flight, they start their quest for a host for her new colony. Finding a place as fast as possible contributes to the survival of the both queens and host plants. For the ant queen, flying towards the wrong plant species or finding a colony already occupying a host translates into wasted energy and increased competition.

So, how do plants advertise available spaces to the founding queens, especially when host plants are dispersed over large areas? What signals are queens recognising? Communication between plants and ants is mostly mediated by volatile chemical compounds (Heil and McKey 2003; Edwards et al. 2006). In our study, we wanted to test if the plant chemical signals that attract ant queens vary depending on the plant’s developmental stage and if queens respond to such variation. Every new generation of founding queens must be capable of distinguishing the most suitable available host from a pool of hundreds of other plants across large distances. It is a question of survival for both ants and hosts, requiring that the mechanisms of recognition and attraction are precise and informative to be successful.

To help us understand ant-plant communication, we studied Pseudomyrmex mordax queens to test their preferences between young and mature leaves or seedling and adult Triplaris americana plants. Pseudomyrmex is a genus of ants restricted to the Neotropics. Some species of the aggressive Pseudomyrmex nest inside myrmecophyte plants like Acacia, Cordia, Tachigali, and Triplaris, (Ward 1991, 1999) and tend coccids (Hemiptera) to obtain sugar. To survive, P. mordax must form a mutualism with T. americana and it is such a good guardian that has made Triplaris earn the name of “vara santa” (or holy rod) as the colony members will painfully sting however comes into the plant’s proximity.

For the experiments, we collected young and mature leaves from both seedling and adult T. americana trees from a population in Colombia. We also collected alate P. mordax queens from the branches of nearby T. americana trees that were not used for the experiment (as we were subject of the ants’ aggressiveness). In an experiment conducted in the field, we placed the leaves of the young and mature T. americana on opposite sides of a two-sided olfactometer and recorded the time each queen spent on each side. We also performed the experiment leaving one of the sides empty as a control. We then compared the differences between the time on each side across all the queens used in the experiment to establish whether the young ant queens had a significant preference for a particular leaf age or plant age.

We found that while queens do not show a preference for young and mature leaves from the same plant, they do prefer leaves from T. americana seedlings over adults. Queens also spent more time in the arm of the olfactometer containing T. americana leaves when the other arm was left empty. Our findings show that P. mordax queens are attracted by volatile chemical compounds produced by T. americana and discriminate signals produced by its seedlings from other signals. The ability to distinguish between plant development stages, along with the use of chemical cues to find a mutualist plant partner increases the chances of a queen’s survival. For the seedling, the ant queen and her future colony provide early protection against herbivores and competition by pruning competing plants, enhancing seedling survivorship. Knowing the age of plant that the queens prefer is only one part of the story. Comparing the relative abundance of the chemical volatiles from each type of leaf will provide more information about how the plant uses odors to signal the queen to her new home.

References

Chomicki G, Renner SS (2015) Phylogenetics and molecular clocks reveal the repeated evolution of ant‐plants after the late Miocene in Africa and the early Miocene in Australasia and the Neotropics. New Phytol 207(2):411-424

Edwards DP, Hassall M, Sutherland WJ, Yu DW (2006) Assembling a mutualism: ant symbionts locate their host plants by detecting volatile chemicals. Insect Soc 53:172–176

Heil M, McKey D (2003) Protective ant-plant interactions as model systems in ecological and evolutionary research. Annu Rev Ecol Evol S 34:425–553

Ward PS (1991) Phylogenetic analysis of Pseudomyrmecine ants associated with domatia-bearing plants. In: Huxley CR, Cutler DF (eds) Ant-plant interactions. Oxford University Press, Oxford, pp 335–352

Ward PS (1999) Systematics, biogeography and host plant associations of the Pseudomyrmex viduus group (Hymenoptera: Formicidae), Triplaris– and Tachigali-inhabiting ants. Zool J Linn Soc 126:451–540