Behavior in Insect Mimicry

Transcription

1 Gendernalik 1 Behavior in Insect Mimicry Alex Gendernalik Alex.Gendernalik@colostate.edu Keywords: mimicry, batesian, wasmannian, peckhamian, aggressive, ant, spider, firefly Abstract Arthropods use insect mimicry to gain predatory advantages over other insects in the form of increased resource availability and protection from predators. They do this through several different mechanisms, 4 of which are described in the paper; Batesian, Peckhamian, Wasmannian, and Tephritid mimicry. Mimicry includes resemblances in both appearance and behavior. Without mimicry in both appearance and behavior (given both are displayed by the model) the organism will be unsuccessful in mimicking its selected model 1. This was shown through Greene and Mather s research on tephritid flies and salticid spiders. Appearance and behavior must be conspicuous to be detected by the deceived. Photuris fireflys and Portia spiders use aggressive mimcry to lure their prey near to them. Then they capture their prey and enjoy the meal. This type of mimicry is not as common as Batesian mimicry but a very interesting strategy nonetheless. Ants are especially formidable prey. Their defenses are strong and relentless, which keeps them safe from common ant predators (birds, other arthropods, etc.). A successful mimic of an ant would enjoy the same protection from predators. Several different spider families have evolved to do just that. 1. Mimicry, as described in this paper, is developed over the course of thousands of years through the mechanism of natural selection. It is not a choice made by the organism.

2 Gendernalik 2 Introduction Over thousands of years arthropods have developed a practically infinite number of strategies for surviving and reproducing and in doing so they have become the most successful phylum, containing the most successful class; the insects. Every organism in the animal kingdom has evolved to fulfill a particular niche. As organisms speciate and as ecosystems change new niches become available and new species evolve to fill those new niches. No matter how obscure or seemingly insignificant the opportunity, something will evolve to take advantage of the new niche. Interactions between organisms can have infinite numbers of outcomes, which outcome occurs depends on the abilities of each organism. The organisms will evolve until one has an advantage over the other or until they develop a mutually beneficial relationship. Insect mimicry is one of the greatest examples of natural selection. It allows the observer to visualize the available niche and determine what adaptations were necessary to fill that particular niche you only need to observe the model, the mimic, the predators and their behaviors. Insect mimicry is generally defined as the resemblance to a model through color, pattern, body structure, behavior or any combination of the previous characteristics. All mimics gain some fitness through their mimicry abilities and there are many advantages to mimicking an insect. Mainly, mimics are protected from predators and (or) have the ability to deceive their prey, their mimicry grants them the ability to have more success in capturing prey.

3 Gendernalik 3 Types of Insect Mimicry In this review I will concentrate on implications of behavior in four types of insect mimicry; (1) Batesian mimicry, (2) Peckhamian (aggressive) mimicry, (3) Wasmannian mimicry and (4) Tephritid mimicry 2. In Batesian mimicry, described by Henry Walter Bates in 1861, the model is distasteful or venomous and the mimic is not. Predators learn to associate the appearance of the model with unpalatability. Ultimately, the palatable mimic is protected because it resembles the unpalatable model. Aggressive (Peckhamian) mimicry was described by Poulton in 1890; it was Poulton who coined the term Peckhamian mimicry because his work was largely based on the observations of E.G. Peckham (Rettenmeyer 1970). Cases of aggressive mimicry involve a harmless looking mimic (resembles the model or another harmless species) that uses its harmless appearance to either lure the prey to within attacking distance or to safely enter the prey s nest, web, or territory to devour the prey and any resources the prey has collected. In Wasmannian mimicry (described by Eric Wasmann and termed by Rettenmeyer in 1970) the mimic resembles the model in order to enter the models territory and either hide among the crowded colony ( schooling in fish) or feast on the models resources. The mimic is not always harmful to the host they may sure a mutually beneficial relationship 2. Tephritid mimicry has only been termed such by the author for the purposes of this paper.

4 Gendernalik 4 In Tephritid mimcry (unofficially termed by the author for the purposes of this review), described by Eisner, is a unique form of mimicry in which the mimic (fruit fly) resembles its predator (the jumping spider) in order to escape predation by the jumping spider. Mimic Behavior A common perception when one hears the word mimic, is that of creatures that have evolved to look identical. This is true; most mimics do physically resemble each other. However, the organism also mimics the models behavior. Morphological or structural adaptations are additional to foremost behavioral adaptations (Mayr 1970). This is easy to consider, a population or community of individuals will always adapt or evolve its organism behavior to fit its new niche prior to the evolution of its organism structure. In the examples below, the displayed behavior of the mimic is a semi preadaptation the type of behavior (grooming, courtship, time active, etc.) was already in use by the mimic before it evolved into mimicry behavior. Mimics tend to display the model s most conspicuous characteristic (Rettenmeyer 1970). In many insects, the most conspicuous characteristic is their behavior. For example, an ant moves in curious, zigzag maneuvers as it scans the ground and sky for direction cues a jumping spider moves in fast, jerky maneuvers as it hunts for prey to pounce on. In fact, these exact conspicuous behaviors are mimicked by other species of jumping spider and flies, respectively. Most insects have very poor eye sight these insects rely on conspicuous body structures, color patterns and the behavior of their potential prey to identify whether or not their prey is palatable. This suggests that small changes in behavior or body

5 Gendernalik 5 structure/color would be undetectable to most insects - obvious behavior (relative to the observer) and colorful or large body structures are most important in insect mimicry. Tephritid Mimicry Even an insect with extraordinarily acute vision, such as the territorial jumping spider (Salticidae), can be fooled into thinking it s facing a conspecific by a few cryptic patterns and some confusing behavior exhibited by the mimic. The tephritid fly mimics a jumping spider by raising its wings to reveal salticid leg-resembling patterns, spots on the end of its abdomen mimic the eyes of a salticid jumping spider. The fly also closely mimics the leg waving and jerky movements of a jumping spider by moving its wings up and down and dancing from side to side when disturbed (Mather and Roitberg 1987). A jumping spider displays the same jerky behavior when another salticid enters its territory, likewise, a salticid that wanders into another s territory will display back before retreating, each encounter usually begins with leg waving and ends with a retreat. A salticidid that encounters a conspecific will usually retreat because the first salticid inhabitant is always dominant size not being an issue (Mather and Roitberg 1987). Many flies use wing flicking (leg waving to jumping spiders) and wing markings displays, especially common in courtship of tephritids (Greene, Orsak, Whitman 1987). It is possible that the tephritid mimicry of salticids was a small evolutionary step from courtship behavior to salticidid mimicry. In their experiments, Greene, Orsak, and Whitman tested the effects of wingwaving and wing patterns on the behavior of salticid spiders by gluing housefly wings (no leg resembling patterns) on tephritids and releasing a salticid in the same area. In most cases the spider attacked the tephrited with housefly wings despite its defensive

6 Gendernalik 6 display. Likewise in most cases, the spider attacked houseflies that had tephritid wings glued onto them. Mather and Roitberg s experiments show that tephritid flies require both behavioral and visual mimicry to be effective in deterring salticid spiders. The tephritid fly has evolved to use the territorial displays of jumping spiders to its advantage by mimicking its own predator in order to deter it from attacking, which is a rarely reported case (Mather and Roitberg 1987). Greene, Orsak, and Whitman (1987) postulated that displays of tephritid mimicry of salticids might also deter other common fly predators (other spiders, Assassin bugs, Mantids, and lizards), this theory was proven false when the research team put salticid mimicking tephritid flies in the presence of the aforementioned predators in almost every case the predator attacked and killed the tephrited fly. Aggressive Mimicry The behavior of the salticid spiders of the genus Portia poses an interesting example of aggressive mimicry. The diet of Portia consists mostly of other spiders and their captures, which is quite unusual as most salcitid spiders prey on insects (Jackson and Pollard 1996). Portia uses a combination of camouflage and aggressive mimicry to fool its prey into believing it is a piece of debris caught in the web and then trick the prey by luring it closer through mimicking web vibrations of ensnared insects. Portia uses its palps, legs, and abdomen to manipulate different vibrations sent through the web when the resident spider responds to a certain vibration pattern. This behavior is thought to be an adaptation of some grooming behaviors, which closely resembles the insectmimicking behavior of Portia on resident spider webs. After the resident spider responds to a certain vibration pattern, Portia begins to continuously reproduce that pattern, luring

7 Gendernalik 7 the spider closer. Portia may then pounce and devour the resident spider, its eggs and any other prey that has been stored in the web. Females of the firefly genus Photuris mimic the flashing patterns of female Photinus fireflys to lure Photinus males that are searching for mates. The female Photuris firefly then devours the male Photinus firefly (Lloyd 1984). The female Photuris firefly has the ability to lure different [male] species of the genus Photinus by changing her flash-delay to mimic the female flash-delay of the [male] species she is trying to lure. Upon capture, the female Photuris firefly eats the Photinus male to obtain chemical compunds called lucibufagins. Lucibufagins, synthesized in Photinus but not in Photuris, are important to the survival of both genera. Lucibufagins, defensive chemicals that are secreted when the firefly is disturbed, are particularly distasteful to common firefly predators (spiders and birds). The female Photuris fireflay needs something that she can only get from the male Photinus firefly this is similar to most aggressive mimicry interactions but instead of requiring food for survival, the female Photuris firefly also requires the lucibufagins to defend herself from hungry predators. Myrmecomorphy (Batesian and Wasmannian Mimicry) Ants are an especially undesirable prey powerful defenses such as distastefulness, aggressiveness, strong biting jaws, venomous stingers, and highlyeffective group defense strategies keep them safe from common predators that rely on visual cues to trigger attack predatory behavior (such as birds and other arthropods). There are over 2000 species of arthropods that have been described as myrmecomorphic (McIver and Stonedahl 1993). It is no wonder that an organism would be more successful if it were to emulate this highly successful arthropod. Such is the case in a number of

8 Gendernalik 8 spider families that not only mimic ant morphology and appearance but ant behavior as well. Complete mimicry of the model (mimicry of both model appearance and model behavior) is necessary to completely fool the mimic s predator. Myrmecomorphy has evolved at least 15 times in spiders (McIver and Stonedahl 1993). These spiders exhibit several types of ant mimicry. Some mimic ants only for protection from predators (Batesian mimicry). Others mimic ants so as to blend in with the ant colony to escape predation (Wasmannian mimicry). Spiders of the genus Myrmarachne prey on the ants that they mimic (aggressive mimicry). All of the myrmecomorphic spider species display behavioral and morphological mimicry of ants (Cushing 1996). Modifications of the legs and body segments give myrmecomorphic spiders the characteristic ant look of 2 body segments and short ant-like legs. They wave their skinnier front legs around in front of them to give them the look of ant antennae thus reducing their number of perceivable legs from 4 to 3. Their movements are curious and erratic, like those of an ant. After the spiders have fooled the ants into thinking they are harmless, the spiders will engage in their particular predatory behavior. Spiders of the species Arnyciaea forticeps stand partially erect and wave their front antennal legs, which attracts workers, when a worker nears the spider pounces. Another genus of myrmecomorphic spider, Oecophylla sp. carries dead ants nearer to groups of ants, the dead ant attracts other ants and the spider attacks them (Cushing 1996). Spiders of the genus Zodarion are Batesian ant mimics, but when capturing prey they use aggressive mimicry. Zodarion has developed a way to sneak past other ants while carrying its own dead ant prey. If a curious ant approaches Zodarion when it is transporting its prey, the spider will tap the antennae with its front legs, cueing the curious ant to observe the

9 Gendernalik 9 myrmecomorphic spiders prey which the spider presents. The corpse of the ant transmits an olfactory cue when the curious ant investigates it. The curious ant then leaves the dead ant and the spider is left to escape with its prey (Pekar and Kral 2001).

10 Gendernalik 10 References Cushing, P.E. (1996). Myrmecomorphy and Myrmecophily in Spiders: A Review. Behavioral Ecology Smposiums 96: Cushing Eisner, T. (1985). A Fly that Mimics Jumping Spiders. Psyche. 92, Eisner, T., Goetz, M.A., Hill, D.E., Smedley, S.R., Meinwald, J. (1997). Firefly femmes fatales acquire defensive steroids (lucibufagins) from their firefly prey. PNAS Greene, E., Orsak, L.J., Whitman, D.W. (1987). A Tephritid Fly Mimics the Territorial Displays of Its Jumping Spider Predators. Science, 236, Jackson, R.R., Pollard, S.D. (1996). Predatory Behavior of Jumping Spiders. Annual Reviews of Entymology. 41, Kral, J., Pekar, S. (2002). Mimicry in two central European zodariid spiders (Araneae: Zodariidae): how Zodarion Deceives Ants. Biological Journal of the Linnean Society. 75, Lloyd, J.E. (1984). Occurrence of Aggressive Mimicry in Fireflies. The Florida Entomologist. 67 (3), Lloyd, J.E. (1975). Aggressive Mimicry in Photuris Fireflies: Signal Repertoires by Femmes Fatales. Science. 187, Lloyd, J.E. (1965). Aggressive Mimicry in Photuris: Firefly Femmes Fatales. Science. 149, Mayr, E. (1970). Populations, Species and Evolution: An Abridgment of Animal Species and Evolution. Belknap Press Cambridge, Massachusetts. McIver, J.D., Stonedahl, G. (1993) Myrmecomorphy: Morphological and Behavioral Mimicry of Ants. Annual Review of Entymology. 38, Nelson, X.J., Jackson, R.R., Li, D. (2006). Conditional use of honest signaling by a Batesian mimic. Behavioral Ecology. 17, Rettenmeyer, C.W. (1970). Insect Mimicry. Annual Reviews of Entymology. 15,