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Month: October, 2012

Popular shows such as So You Think You Can Dance and Dancing with the Stars have illustrated that there is an extremely wide range of dancing styles. From samba to ballet, and hip hop to tap, there are many forms of dancing in which humans engage. Similarly, honeybees have multiple forms of dancing that they use throughout their lives. Last week we discussed the waggle dance, however this week’s focus will be the shaking dance. Robert Gahl describes the shaking dance as a dorsal-ventral abdominal vibration of the honeybee by means of rapid contractions of leg muscles and pivoting of the legs (Gahl, 230). This dance, enacted by worker bees, can be performed alone, on top one other bee, or atop several bees. A previous study done by Allen, M. indicated that, for dances atop other honeybees, there is no age relationship between the shaker (intiator of the shaking dance) and the bee shaken. In other words, the individual shakers did not tend to shake a particular age-range of worker bees. Contrastingly, Gahl found just the opposite.

Gahl’s study was performed on a small observation hive in which 820 bees were color-marked and uniquely numbered to provide an accurate indication of age. Data collected included the shaking situation (if the bee performed the shaking dance alone, on one other bee, or on several other bees), the age of the shaker, and the age of the bee shaken (if the shaking dance was performed on other/s). Over his 28-day observation, 4949 shaking dances were peformed: 2039 shaking dances were performed alone (41.2%), 2220 were performed on one other bee (44.8%), and 690 were performed straddling more than one bee (14%) (Gahl, 231). Gahl focused on the shaking dances performed one-on-one. (Why he did not look at the other two categories in further detail, I am unsure of.) In regards to correlationship with age, the results were as followed:

The included graph shows the age difference between the shaker and the recipient. A positive number indicates that the shaker was older than the recipient while a negative number indicates that the shaker was younger than the recipient. As you can see, the age difference between the two bees ranged from -9 days and 22 days, with less than 4% of the shaking dances performed on bees older than the shaker. The bees would shake other bees up to 22 days younger than them, however they would not shake any bee older than 9 days.

From this graph, we see that the ages of shakers ranged from 0 to 24 days and the ages of receivers ranged from 0 to 26 days. The majority of shakers were between 9 and 19 days old, while most of the bees that were being shaken were 2 days old. Thus, Gahl’s research shows that “a relationship has been found between the age of the shaker and the bee shaken, the shaker being nearly always older” (Gahl, 232). According to Gahl, shaking is not performed randomly, but with some discrimination determined by age. Some sort of age recognition is taking place within the hive and among the bees. My question is, why have this age recognition? What purpose does it serve? Gahl did not provide any explanations on this other than his results may relate to the function of the shaking dance. In other words, because this shaking dance seems to be driven by certain age-related rules, the purpose of the shaking dance may have something to do with such age discriminations. Is it to train younger, less experienced bees for something? Is it a type of information sharing? Is it a way of exhibiting dominance and therefore establish a type of hierarchy among the bees in the hive? In addition, how do the shakers do this type of age-discrimination? Gahl proposes that the shakers know based on the physiological variation of bees differing in age, traits such as “strength, health, glandular growth, or labour category (which is partially related to age and partially to food conditions in the hive), or some combination of these” (Gahl 232). I wonder if age could also be discriminated by pheromones or other nonvisual cues such as the way the buzz or the pitch at which they buzz.

However, the interesting thing about this article lies in the fact that there is a type of age-discrimination going on, regardless of how this is accomplished or its purpose. This illustrates the intricacies of communication. It is not a simple process that can be generalized over one species. Many things come into play, such as the absolute age of the communicators, and even their ages relative to each other. This is also seen in humans as well. We communicate with people differently based on our ages. There are certain rules to follow when speaking to an elder, and there are particular ways in which we speak to those younger than us. Although much of these rules are socially contrived, communication in itself is a social process.

Gahl, R. A. (1975) The shaking dance of honey bee workers: evidence for age discrimination. Animal Behavior, 23(1), 230-232.

—————————-UPDATE—————————-
On second thought, could this be just a correlation? Maybe the shaking dance is not discriminatory via age. Instead, it may be something completely separate that is correlated to age. Just a thought.

Waggle Dance

For humans, dancing can be a form of communication that conveys a lot of nonverbal information.  Although we mainly partake in dancing for entertainment reasons, we must not forget that it is guided by social conventions and conceived guidelines.  Therefore, our bodies can say a lot more than we think based on how we move.  Honeybees, too, use dancing as a means to communicate with one another.  Although it is less for entertainment as it is for survival, they follow certain social patterns and expectancies just as humans do.  Jacobus Biesmeijer and Thomas Seeley’s research on the waggle dance of honeybees illustrates that honeybees use a form of dance in three situations when foraging for food.  The followers of the waggle dance “can use location information acquired from the dance to find the indicated food source” which in turn “contributes to the foraging success of a honey bee colony” (Biesmeijer & Seeley, 133).   Information on the type of food (pollen vs. nectar), the direction, and the distance of the food source can be conveyed through this dance.  They studied the following three contexts:

1) The novice forager finding its first food source

2) The experienced forager whose foraging expedition has been interrupted

3) The experienced forager that is engaged in foraging

In all three contexts, the honeybee can either use the waggle dance information to guide its search or search independently for a food source without following any dance.

Biesmeijer and Seeley set up an observational hive in which the bees were forced to enter and leave the hive from one side of the cove.  Consequently, all of the nectar unloading and all of the dancing could be recorded methodically.  They performed three trials of observation: during the spring, summer, and fall.  Depending on the trial, thirty or sixty bees were labeled for individual identification. The observer noted the following of a waggle dance if a bee was within one bee length of the dancer, faced the dancer, and moved so that its head always faced the performing dancer.  Honeybees that had early excursions shorter than ten minutes and did not unload nectar or pollen upon return (thus performing an orientation flight) were considered novice foragers.  The 48 novice foragers were observed from when their attempts of foraging began until when they engaged in successful food collection.  Nineteen of those honeybees, or 40%, attempted to forage without the aid of information from any type of waggle dance.  Eighteen honeybees, or 37%, relied on the waggle dance of other bees.  The remaining 11 honeybees, or 23%, relied evenly on both.  It is interesting to note that although there were differences in how the honeybees foraged for food, they did not differ statistically in the number of search trips, around 4.3 trips, required to find their first food source (Biesmeijer & Seeley, 136).

Sixty-three experienced foragers were observed on the 512 days determined as interrupted forager days.  The behavior of interest was how the honeybees went back to foraging, if they followed a waggle dance to resume or if they went independently to find the same source.  63% of the time, the bees made trips that were not preceded by the following of a waggle dance, while 37% of the time, the bees made trips preceded by the following of waggle dance (termed reactivation).  They found through statistical analysis that success was only slightly (but not significantly) higher for reactivation trips (preceded by the following of a waggle dance) than for trips that were not preceded by the following of a waggle dance (Biesmeijer & Seeley, 137).  Looking at the trends over the whole day, experienced foragers followed the waggle dance for 16.6% of their daily trips when there were no interruptions.

When looking at the overall foraging activity for each experienced forager over their lifetime, Biesmeijer and Seeley found that “the percentage of first trips [of the day] by reactivation decreased over days of foraging” for most of the trials (trials 1 and 3)(Biesmeijer & Seeley, 137).  In other words, experienced honeybees that lived longer tended to decrease their following of the waggle dance before going out on their first foraging trip of the day.

It is also interesting that Biesmeijer and Seeley found “dance following much more common after a failed trip [. . .] than after a successful one” (Biesmeijer & Seeley, 137).  Honeybees that did not follow a waggle dance and failed to find food were 22-33% likely to follow a dance before their next trip.  If the honeybees were successful however, that probability of following a waggle dance before their next trip dropped to 6-8%.  The same trends were found even for honeybees that did follow a waggle dance initially.  Honeybees that followed a waggle dance and failed to find food were 60-80% likely to follow a dance for their next trip.  However, if the honeybees were successful in finding food, that probability dropped to 22-44% of following a waggle dance for their next trip (Biesmeijer & Seeley, 138).

After reading the results, let’s revisit the purpose of the study: to examine the extent to which worker honeybees acquire information from waggle dances throughout their careers as foragers (Biesmeijer & Seeley, 139).  As a recap, we found that 37% of the novice foragers followed a waggle dance to find their first food source, experienced honeybees followed waggle dances 37% of the time after their foraging was interrupted, and experienced foragers followed dances before 17-20% of their trips, especially if their previous trips resulted in no food.

Biesmeijer and Seeley’s results provide some interesting discussion topics.  First of all, although only 37% of novice bees relied on the waggle dance to find their first food source, if no food source were found, they were more likely to follow a waggle dance for their next trip.  On average, it took novice honeybees 4.3 trips to find their first food source.  Therefore, I hypothesize that if we were to graph the behavior of bees over trips, we would see a slight increase in the following of waggle dances until that 4.3 marker and then a decrease (since the results showed that if successful in finding food, honeybees were less like to follow a dance after).  This decrease would continue since the results also showed that experience honeybees who lived longer and gained more experience were less likely to follow waggle dances.

Another topic I would like to discuss is the availability of waggle dances, in other words, how many of the honeybees that knew the location of food sources actually produced a waggle dance.  This number would alter how many honeybees followed the dance such that if there was a high availability of dancing bees, the amount of honeybees following the dance would be higher than if there were not that many honeybees producing the waggle dance.  In addition, that could say something about the evolutionary history of the waggle dance.  The balance between the amount of waggle dance produced and the amount of following would, I assume, be tweaked through evolutionary forces.  With too much dancing available, this would take up unnecessary time and energy of the dancing bees which they could be devoting to other tasks.  However with too little dancing available, the following of the dance would be inefficient if there were not enough dances to learn from.

I also wonder why such a phenomena occurs if the success of finding food does not differ that greatly between the followers of the dance and those that did not follow the waggle dance.  Does this communication system benefit the bees in a different way?  Even if both the follower and the non-follower brings back food with the same probability, does following the dance allow the bees to find the food faster?  Biesmeijer and Seeley offer the following explanation: recruitment (following the waggle dance) “guides a bee to a much richer food source [. . .] and lets a bee avoid the cost of inspection flights” (Biesmeijer & Seeley, 141).  However, they do admit that only through further study will they be able to make a stronger hypothesis regarding the relative benefits of the waggle dance and how it improves the economy of the colony.

Biesmeijer, J. C. & Seeley, T. D. (2005) The use of waggle dance information by honeybees throughout their foraging careers. Behavioral Ecology and Sociobiology, 59(1), 133-142.

And We Meet Again!

As you read the words I have typed, we are engaging in a type of communication.  Due to technology, we have many forms of communication that were unfathomable to our ancestors such as text messages, emails, and online blogs such as these.  Inarguably, communication is extremely important for our everyday lives and the continuation of our species.  Other animals, too, depend on successful communication with each other and have varying systems of communication.  While walking to class we may hear birds chirping and not realize the importance of their songs.  In fact, forms of communication are not as simple as one may assume.  Many factors come into play that allows the environment of a species to guide the evolutionary history of a particular system of communication.

Endler sums up communication nicely saying that animal communication systems have evolved so that individuals can make decisions based upon the behavior, physiology or morphology of others (Endler, 215).  However, what are the factors that guide the evolution of such systems?  In my blog, I will discuss the following factors in more detail: those that affect the quality of the received and processed signal, those that affect how the signal is generated and emitted, and those that affect how it fares through transmission through the medium.  In essence, the “factors that affect signals [. . .] constrain or bias the direction of evolution of signals and signaling systems” (Endler, 215).  The phylogenetic history of a species works hand in hand with the geological time a clade spends in the signaling environment to produce a specific type of signaling design.

I argue that the production of a communication signal is of most importance.  Why?  Because regardless the quality of the receiving system, if the signal produced is not of good quality, then the effectiveness of communication is automatically destroyed.  For example, if you have excellent ears but I cannot form coherent sentences, the information does not get past my lips no matter how well you can hear.  Many things affect the generation of a signal such as the physics, biophysics and chemistry of the producing signals for example.  If it becomes physically impossible for a signal to be produced, then that mode of signaling will not be successful and therefore will not be selected for.  Instead, the physical structure of the signal evolves to increase the efficacy of transmission of the message between emitter and receiver (Endler, 215).  Efficacy, however, is not as clear cut as it may seem.  If a signal is energetically costly, one may assume that that form of communication will be lost or weakened.  However, if there are beneficial trade-offs between the present and future fitness for that species, then there can instead be a bias for things like the time, place, or age of the signaling, and that form of communication can exist and continue to evolve.

There is another trade off that is important: that between the amount of information in a signal and the clarity of the signal.  (The two components together are referred to as the “quality” of a signal.)  An increase in information is usually achieved via an increase in signal complexity or density.  However, as the complexity increases, it becomes difficult to prevent “noise” or confusion with both the production and interpretation of the signal.  This brings us to the topic of transmission through the medium through which the signal travels.  Environmental constraints can favor signaling during times and places at which things like distortion, attenuation, blocking, absorption, reflection, and refraction are minimized.  These effects are exacerbated if the signal is complex with a high information density, or when information is transmitted at a high rate (Endler 217).

The environment can affect signaling both in a direct or an indirect manner.  For example, the spatial and temporal variation of predation, or climatic and microenvironmental conditions can directly favor signals that maximize emission and transmission of communication signals (Endler, 216).  What I find interesting, however, are the indirect effects environment can have.  Endler exemplifies this nicely, “some environmental factors do not directly affect the signals but do affect the evolution of the breeding system [. . .] If the breeding [is] limited to a small range of environmental conditions, then this will bias the evolution of signals and signaling behavior to work better under those more specific conditions (Endler, 216).

The reception of a signal is also not as straightforward as it seems.  The current adaptive state of the individuals receptor play a huge role in what can and cannot be received.  For example, the present state of an animal’s eyes and the information sent to the brain depends on how much light is in the environment.  If the animal is in a microenvironment with high light intensity, its visual system will be less effective at distinguishing between darker pattern elements than between lighter pattern elements (Endler, 218).  However, if an animal is in a dark microenvironment, it will be less able to distinguish between lighter pattern elements than between darker pattern elements (Endler 218).  In essence, “a given receptor does not always transduce signals into neural outputs in the same way,” and instead depends on the environment the signal is sent through.

According to Endler, “the evolution of a communication system involved three suites of traits: the signals, the sensory and cognitive systems used to receive the signals, and the behavior associated with the signaling” (Endler, 220).  Because they are all interrelated, they tend to coevolve, and an effect on one will cause an effect on the other two.  Communication is not just about one factor or the other.  Instead, it is a network that balances these three main components.  To sum up this blog post, “the direction of this joint evolution [is] set by the biophysical and energetic conditions of signal emission, environmental conditions which favor clarity of reception, neural conditions which favor the processing of certain kinds of signals or signal components, and the strategies behind signal emission, detection, discrimination, and decision making” (Endler, 222).

This post is just an introduction to animal communication, to provide context and a better understanding of the following blogs.  As the quarter unfolds, what was discussed in this blog should be kept in the back of the mind.  Animal communication may be taken for granted, however, just in this introduction, we’ve learned that it is far from simple.  Its many intricacies must be appreciated when learning about the communication form in different species.  Each communication system had an advantage for the species and the environment that species evolved in.

 

The following is a table of different modes of communication that animals are known to participate in:

 

The following is a table of some factors that affect the efficacy of communication systems:

 

Endler, A. J. (1993). The evolution and design of animal signaling systems. Biological Sciences, 340(1292), 215-225.