Communication Methods in Fireflies and Their Applications

Transcription

1 Communication Methods in Fireflies and Their Applications 1. Introduction Ross MacGregor Mechanical Engineering, CSU Abstract. Social animals and insects utilize different forms of communication in order to achieve tasks such as locating food, avoiding or defending against predators, or finding willing mates. In order to communicate with others, insects use a variety of methods including the use of scent, sounds and motions. The firefly uses a unique bioluminescent body part to convey messages to other insects. The ability to illuminate is the result of a chemical reaction of primarily oxygen, Mg+2 and ATP [2]. The flashing ability of the firefly is primarily used for courtship, using specific timing to communicate details of the mating process to the opposite sex [5]. However, female fireflies have been shown to modify their flashing timing to mimic the timing of another species to attract prey [14]. The fooled prey is expecting a female mate but is greeted by the carnivorous female firefly. Although most adult fireflies use photic signals for sexual communication, the firefly has the ability to illuminate during the larval states as well but the larva have no intent to mate during this period. This lead to theories of alternate uses of the illumination. It is possible the illumination is used to deter predators of the unappealing taste of the larva [2][8]. Communication takes many forms throughout different animals and insects. Despite the communicative form, they all share the same purpose, to transmit thoughts or information from one mind and being received by another [18]. The human mind is capable of many forms of communication, as well are insects. Comparing communication forms of one species to another can yield some interesting results. This paper will briefly introduce and discuss some similarities of firefly and human communication methods. Male and female fireflies of various species use flashing signals to achieve tasks essential for survival. The details within the flash signals are different among the species, but the main uses are common throughout. The primary use of the flashing ability is for communication of sexual status to opposing genders of the same species. Other uses for firefly flashes have been found to include larval defense mechanisms and aggressive mimicry used for luring fooled prey in search of mates. These topics will be further described in this paper. 1

2 The act of communicating through flashing has intrigued many researchers in the past. Thorough investigation of the flashing communication method has led to a relatively complete breakdown of the codes sent and received by both male and female fireflies. However, one aspect of the communication between males and females that has not been studied is how a message can be sent and be accurately interpreted despite errors in the sending and the abundance of noise encountered in the environment. The task of filtering out a single message sent by a similar species of firefly while being bombarded with hundreds of other flashing signals is a fascinating act. This topic will be discussed further in the paper, but since the topic has not been studied in depth the material will be mostly theoretical. 2. Science of the Flashing Abilities In the larval stage, fireflies are able to illuminate but the flashes take on a different role in adults. Since a major use of the flashing is for courtship the ability to control the flashing with enough precision to communicate is not needed until the adult stages of the insect s life [13]. Thus, the insect is not able to flash precisely until adult stages. The ability to create an illuminating light source from within the insect body is a rarity. There are about 30 known animal species that posses the ability, most of which are marine creatures [4]. Though there are different species of fireflies, the illuminating chemical reactions are similar. The ability to illuminate is the result of a chemical reaction of primarily oxygen, Mg +2, and ATP [1]. This reaction is triggered from the result of another process. Neural impulses lead to the release of a neurotransmitter octopamine into the illuminating body part. The article [13] states that Recent work suggests that octopamine release causes a transient increase in production of nitric oxide, a rapidly diffusing gas that may switch on the flash by allowing oxygen to reach the luciferin-luciferase reactants housed within the lantern photocytes. This 2

3 statement leads to the point that illumination in adults is both anatomically and physiologically specialized. 3. Uses and Methods of Flash Communication The action of communication has been described as the transmission of one mind s thoughts and being received by another mind [18]. Within the human species, some form of communication is constantly being experienced and is nearly impossible to avoid in the daily routine of most people. Humans are able to communicate through a number of mediums; some examples include but are not limited to: speech, music, theater, television, telephone, mail, electronic mail, and internet postings. There are also methods to communicate not involving spoken word but body language and visual cues. Whatever medium is used, communication in humans relies heavily on a form of language. Humans have formed many languages capable of expressing detailed information. However, communication is different for insects. Many insects rely on scents, visual cues, textures, and sounds to transmit messages. The firefly for instance, uses a unique ability of flashing light to transmit information. Each firefly utilizes one lantern, which only has two positions, on and off. Though most humans would struggle to communicate only through the use of one blinking light (unless one happens to know Morse Code), the firefly uses this as a primary means of communication to transmit a variety of information. 3.1 Larval Stage Defensive Flashing The firefly larva are able to illuminate similarly to the firefly adults, however, the process has some key physical and functional differences. The lantern is not contained within the sixth and seventh abdominal sternites as it is within the adults, but in the eighth. Early in the life of 3

4 the firefly, the ability to regulate flash timing accurately has not been acquired. The larva illumination is not a clean and precise flash as the adult illuminations are, but are a more subtle glow activating for longer periods of about few seconds. The ability to illuminate during a larval stage seems to be counter intuitive to what one would usually consider an effective defensive behavior. It appears the larvas are essentially advertising the location for predators to acquire food by illuminating the lantern for long periods of time. This is actually the opposite route many insects take to survive the attack of predators. Although this is true, illuminating as larva has a useful purpose. The firefly larvas have an unpalatable or unappealing taste to predators. Predatory animals have been found to discover this foul taste and assign the illuminating insect to an unappealing taste. This has proven to be an effective method to deter predators from eating the firefly in the vulnerable larva stage. 3.2 Mating The use of flash communication for finding sexual mates is the routine most often observed with many species of fireflies. The search for mates occurs at night and involves males and females flashing messages advertising the individual s sexual status and location. This process is inherently relatively easy to see and investigate in the field, resulting with the performance of many experiments seeking to decode the flashing behavior General Sexual Communication Routine The firefly s process of finding a mate begins with males roving at night flashing a message specific to their species, advertising they are looking for a female mate [17]. The females are sedentary during this process, usually in a high location allowing for more efficient 4

5 flash sending and receiving. Based on certain qualities associated with the male s flash, such as pulse length and time between pulses, the female will respond to the attractive males with her own flash sequence [17]. It has been found that in certain species of firefly males with higher flashing routine frequency rates generally have higher mating success rates [10]. At this point in the firefly conversation the male will move towards the female and continue the flashing. However, it is common for more than one male to respond to the female s flashing resulting in competitive behavior [10]. There have been studies performed to investigate what characteristics of firefly males contribute to a successful competition situation, but conclude different reasons [13]. These differences in conclusions could be attributed to differences in species. Courtship periods generally last for one to two hours nightly, during which males and females will often sample numerous possible mates. However, the actual mating process generally will occur once a night [17] Timing Routines As discussed before, fireflies facilitate different flashing routines specific to their species in order to find mates. The signaling patterns in males are temporally impeded similar to many acoustic and vibration signals used for courtship in other insects [11]. Figure 1 below shows a breakdown of the different signal timing routines used by a number of species of photinus. It should be noted the female response patterns are displayed on a different time scale and the beginning of the response scale indicates the time of response from the last male flash. The information in Figure 1 is a compilation of information from [16][15][1][7]. 5

6 Figure 1 - Firefly Species Flash Decoding [13] Examination of Figure 1 allows general trends of the mating flash patterns to be observed. There are variations in the number of flashes, length of flash, and time between flashes in different species. The male in every species produces multiple flashes per pattern. However, the female responses are more commonly a single flash, only the consimilis and carolinus respond to males with multiple flashes. 3.3 Aggressive Mimicry There are certain species of fireflies where females utilize carnivorous eating habits. It has been suggested that the female has the ability to mimic flashing responses of other firefly species, in turn attracting males of other species. Upon the arrival of the fooled male, the female will attack and consume the male. Partaking in aggressive mimicry is not common within all 6

7 species, Photuris fireflies are an example of a firefly that mimics Photinus firefly flash signals [10]. There have been documented instances where it is plausible that different types of species of fireflies have mimicked one another, see [14]. In this article Lloyd claims to have observed, on five different occasions, instances where interspecies communication took place. One occasion actually ended with the female successfully luring a dissimilar species male and consuming it [14]. These experiences were not extensively thorough or consistent. The interactions were usually induced by flashing different patterns with a flashlight. Nonetheless, some of the experiences seem to support the ability for certain female fireflies to imitate other species. 4. Discussion The communication methods used by multiple species of fireflies have been explained in moderate detail. It was found that fireflies have three primary uses of flash communication: larval warnings, mating, and aggressive mimicking. In the following sections these particular areas of communication will be explored through the eyes of an engineer, attempting to relate the simplistic method of flash communication to other forms common in people s daily lives and their inherent drawbacks. Through this comparison similar qualities and difficulties will arise that are not obvious. Comparing the everyday forms of communication of humans to luminescent beetles might seem peculiar, however, humans have formed many ways to execute communicative processes in very simplified ways. The following sections will introduce some examples of communication styles used by humans that are surprisingly similar to the firefly s flashing. 7

8 4.1 Infrared Data Transmission A common devise used in households is the television set complete with a remote control. The remote wirelessly transmits information indicating which button on the unit is pressed and the electronics inside the television interpret the signal. This method of data transmission is commonly realized through the use of infrared Light Emitting Diodes (IR LEDs). Infrared light has a higher wavelength than that of visible light on the electromagnetic spectrum and is not visible to the human eye. Other forms of data transmission exist in remote controls, but only IR transmission is discussed. These devises operate in binary, which is the language foundation on which all computer s functions are built upon. The number system used commonly by people is of base ten, meaning there are ten characters able to describe one placeholder, the numbers 0 through 9. Binary means there are two characters able to describe a placeholder, usually 0 and 1. This is how the remote control works, it sends out strings, or bytes, of data represented as zeros and ones. Specifically in the remote control, the length of the off period following an on period corresponds to a 0 or 1, respectively [12]. Figure 2 shows a byte sent out by a Sony remote control representing the volume up command. The remote will quickly flash the IR LED as the figure describes over and over, until the button is released. Every button has a different pattern associated with it. Figure 2 - Example of a byte sent by a remote control [12] 8

9 Notice the long periods of the IR LED in the off position before and after the pattern, this paper refers to these periods as identifiers. These portions of the transmission are crucial to the functionality of the remote, without the identifiers the byte pattern will have no beginning and no purpose. It should be noted that this form of data transmission was not created for the specific use in remote controls, and similar methods are sometimes used for communication between microcontrollers. 4.2 IR Data Transmission and Firefly Flash Communication As discussed before, fireflies have the ability to illuminate a portion of their body. This flashing ability has two positions of either on or off. This is essentially a binary mode of transmission, similar to the form of IR communication discussed above. This is immediately quite intriguing. During the search for a mate, male fireflies repeatedly send a specific flashing pattern awaiting the response of an interested female. When a person uses a remote control to change the volume on a television, or a similar action, the remote repeatedly sends out the pattern specific to the command. Once the change has occurred on the television, the person will realize the change and stop pressing the remote control button. This interaction of firefly male to female is very similar to the user and television interaction in this respect. The human being has unintentionally created a style of data communication similar to a style nature has been utilizing for some time. This similarity is not only interesting, but may be useful in diagnosing how a firefly is able to transmit the desired signal despite environmental interference and errors in signal transmission resulting in signal noise. Signal noise is essentially an unexpected disturbance in the signal being transmitted from one device to another. In the realm of electronics this occurs for a number of reasons, a major one being through electromagnetic fluctuations inducing 9

10 sporadic current flows throughout wired connections. An example of when his occurs is when an electric motor is operated within close proximity of a circuit. Signal noise can cause losses of data, sporadic trends and shifted data. As in any form of a serial data transmission, if the identifier preceding or following the data is lost or corrupted due to noise, the data is of no use because the receiver does not know what it applies to. It is reasonable that it could be the same scenario with the fireflies. By examining Figure 1 it is conceivable that if a portion of the transmitted male signals or female signals are lost, it would not be the same pattern and would not successfully attract a male or female. Occasions when this happens are unavoidable. If the male happens to begin the flash pattern when it is turned away from the female, or the line of sight is blocked by a plant or another obstacle the entire pattern would not be communicated properly. Despite these possibilities, the messages do get transmitted or the species would not be alive today. This shows that somehow the fireflies are properly filtering the data signals and communicating with success. There have been limited studies on the filtering abilities of the various firefly species. Perhaps this is so because data transmission and signal noise are not areas biologists are specialized in. People exist who dedicate their life work to efficient data transfer and the science behind this area of study is quite established. The details of the methods are too complicated and specialized for this paper, but to know there are methods that work for filtering out environmental noise in infrared data communication could be useful. Perhaps these methods could be considered when attempting to decode the filtering methods used by fireflies. 10

11 4.3 Larval Warnings Above it was found that fireflies in the larval stage have the ability to flash and use it to deter potential predators. This purely visual cue is enough to relay a message suggesting to the predator that this meal is not palatable and to move on without consuming this beetle. Humans also use many simple and purely visual cues to communicate relatively complex messages. Traffic signals offer a good example. These units are basic and consist of three colors of lights including red, yellow, and green all of which communicate different messages to drivers approaching an intersection. The color red has become a color that drivers associate with stop, yellow is associated with approach with caution or slow down, and finally green is associated with progress or go. This is a bit of a stretch but is a good example of how other species use a simple light signal to achieve a complicated task, whether it is to protect vulnerable larva, or to control a complicated traffic flow. 4.4 Consequences of Signal Noise Related to Mimicry It was discussed above that if a signal is affected by noise, the transmitted data can be useless to the application. However, if the signal is being used by microcontrollers, it will try to use the faulty data regardless if it is bad or good. There are times when this problem is obvious and times when it will go unnoticed. It is obvious when, for example, the program tries to perform a mathematical function on a word. This does not work and the program will crash, making corrupted data obviously apparent. However, say for example the identifier is only slightly different and assigns the wrong byte of data to a slot. This is not so obvious. The program will execute blind to the problem. 11

12 Similar phenomena might be the reason for the mimicking abilities of the fireflies. If a female is responding in a slightly offset timing similar to that of a different species, a male searching for that particular species will approach the improperly signaling female. This is so because that is the fixed action pattern of the firefly male; it is imbedded in the brain. Observing Figure 1 shows that the female responses are all very similar and a mistake during this response flash seems easy to make. Perhaps the females are not intending to mimic the other species but consume the males upon their arrival in a defensive maneuver. This is only a speculation and has not been proven. 5. Conclusion The firefly beetles are made up of a number of different species that all have different behaviors, but share the basic flash communication abilities. The most apparent uses of the firefly s flash communication include larval defense, mating, and aggressive mimicry. All of these flash behaviors were introduced and discussed above in a limited amount of detail. An interesting observation was that the flashing ability is used to both deter predators and lure in prey at different points in the firefly lifespan. This paper introduced the topic of communication and how people use it in day to day life. These methods were broken down into basic forms and compared to the flash communication utilized by fireflies. Initially comparing firefly communication methods to that of humans seemed a stretch, but after further investigation it was found that some forms humans use for communicating messages are surprisingly similar to that of the beetle s forms. After all, communication is transferring information from once source to another regardless of the form or type of encoding used on the information. 12

13 References 1. Branham, M.A. and MD Greenfield. Flashing Males Win Mate Success. Nature Buck, J. Synchronous rhythmic flashing of fireflies. II. The Quarterly Review of Biology. 63(3): Buck, J and J Case. Flash Control and Female Dialog Repertory in the Firefly Photinus Greeni. Biol. Bull. 170: Buck, J. and J. Case. Physiological links in firefly flash code evolution. Journal of Insect Behavior. 15(1): Carlson, Albert D. and Jonathan Copeland. Flash Communication in Fireflies. The Quarterly Review of Biology, Vol. 60, No. 4. pp Dec Copeland, Jonathan and Andrew Moiseff. Flash Precision at the Start of Synchrony in Photuris Frontalis. Integr. Comp. Biol., 44: Copeland, Jonathan and Andrew Moiseff. The Occurance of Synchrony in the North American Firefly Photinus Carolinus (Coleoptera: Lampyridae). J. Insect Behav. 8: ) Day, John C., Laurence C. Tisi, Mark J. Bailey. Evolution of Beetle Bioluminescence: the Orifin of Beetle Luciferin. Wiley InterScience. 10 Nov De Cock R. and E. Matthysen. Sexual Communication by Pheromones in a Firefly, Phosphaenus Hemipterus (Coleoptera: Lampyridea). Laboratory of Animal Ecology, Department of Biology, University of Antwerp. 29 Aug Demary, Kristian, Constantinos I. Michaelidis, Sara M. Lewis. Firefly Courtship: Behavioral and Morphological Predictors of Male Mating Success in Photinus greeni. 2 Sep, Greenfield, MD. Signaler and Receivers: Mechanisms and Evolution of Arthropod Communication. Oxford University Press, Cambridge Layton, Julia. How Remote Controls Work. How Stuff Works. < 30 March Lewis, Sara M., Christopher K. Cratsley and Kristian Demary. Mate Recognition and Choice in Photinus Firelies. Ann. Zool. Fennici 41: Dec

14 14. Lloyd, James E. Aggressive Mimicry in Photuris: Firefly Femmes Fatales. Science, Vol. 140, No pp Aug Lloyd, James E. Flashing Behavior and Additional Species of Nearctic Photinus Fireflies (Coleoptera: Lampyridae). Coleopt. Bull. 23: Lloyd, James E. Studies on the Flash Communication System in Photinus Fireflies. University of Michigan Misc. Publishing. 130: Michaelidis, Constantinos I., Kristian C. Demary, and Sara M. Lewisa. Male courtship signals and female signal assessment in Photinus greeni fireflies. Behavioral Ecology. 18 January Shannon, Claude E. and Warren Weaver. The Mathematical Theory of Communication. The University of Illinois Press, Urbana