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The flight behavior of butterflies reflects the palatability. Butterflies that fly slowly are unpalatable, while butterflies that fly quickly are palatable. Palatability also correlates with the coloration of butterflies. Butterflies with aposematic coloration tend to be unpalatable, or mimic unpalatable species. Butterflies that are cryptic tend to be palatable. Other traits that correlate with flight behavior are shape, distribution of tissues (muscle verses reproductive), the energy requirements, and the preference of habitats. Selection pressures for unpalatable verses palatable butterflies are also different. Whereas unpalatable butterflies are selected for shape that advertises toxins, palatable butterflies are selected for evasive flight. The form of each butterfly must dictate how it defends itself. The selection pressures for each type of butterfly may be different. Unpalatable butterflies are under fitness selection. Palatable butterflies are under pressure to be fast and maneuverable.

The behaviors of the predators must also be examined. Predators are capable of associative learning. They can learn the palatabilities of several local butterflies, so that they will not accidently catch a bad meal. Predators avoid catching unpalatable butterflies even though they flight slowly due to coloration and shape of the butterflies. Predators catch palatable butterflies knowing that they are harder to catch, but that they are not toxic. Predators may avoid mimics, or sample them, depending on the type of mimicry and the experience of the predator. Aposematic coloration is important in predator learning and memory.

The evolution of aposematic coloration may be due to different selection pressures from predators. Several theories are discussed at length. Mimicry can help predators "learn" or can cause predators to ignore previous experiences.

As well as morphological mimicry, small signals from the prey can prevent predators from being interested. This is referred to as locomotor mimicry. Locomotor mimicry is very small movements that may help predators learn the palatability of butterflies.

Defensive strategies of butterflies against predators include chemicals, mimicry, aposematic coloration, and evasive flight (Chai, 1990a). Chemical defense and aposematic coloration are often associated. Chemically defended butterflies may be unpalatable to predators. Unpalatable butterfly mimics benefit from aposematic coloration and chemical defense. Related to unpalatability are flight patterns. Butterfly flight patterns, palatability, and coloration often correlate. Brightly colored butterflies and their mimics fly with heavy, slow movements and no apparent purpose whereas cryptic butterflies fly purposely with fast, strong, erratic movements. Many theories exist to explain why butterflies exhibit different flight patterns associated with coloration and palatability and how mimics benefit.

Butterfly shape (body length/thoracic diameter ratio) may be correlated with flight speed. Butterflies with aposematic or mimetic coloration fly regularly, are often rejected by birds on site, and have slim, lengthened bodies. Cryptic butterflies have an enhanced ability to escape bird predation through fast, evasive flight and often have short and stout bodies (Chai, 1996).

To test the palatability of butterflies an experiment utilized jacamars (Galbula ruficauda) as specialized insectivore predators and butterflies from Papilionidae, Lycaenidae, and Riodinidae as prey. Behaviors of the bird are classified into categories. The categories being tested are the behaviors of the birds when first exposed to the butterfly prey; bird response to the rejected classes of prey; the classification of the butterflies on the basis of palatability; and rapid associative learning in jacamars (Chai, 1996).

Visual cues such as the flight behavior of butterflies often correlate with jacamar consumption. Slower fliers are not often attacked or eaten by jacamars whereas faster flighers are often attacked and eaten (Chai et al, 1990a). In the palatability experiments, jacamars either consumed the butterflies or they did not, indicating that there was a very clear distribution of butterfly palatability. The jacamars elicited a bimodal response to the palatability of the butterflies. The best indicator of bird behavioral response to butterflies was body shape and flight pattern. Slow flying butterflies with long, thin bodies are easily caught, but are also released quickly and not usually harmed (Chai, 1996). The long thorax allows unpalatable species to escape capture by being distinguishable (Chai et al, 1990a). These butterflies had bright coloration. Hard to catch butterflies with short, stout bodies may be evasive, but are quickly consumed when captured. These butterflies have cryptic coloration. It has been suggested that the predator can learn the palatability of prey in association with visual characteristics such as body shape and coloration. The behavioral flight pattern of butterflies may also contribute to this associative learning. Once a jacamar has "learned" the flight characteristics, coloration, palatability, and body shape of surrounding butterflies, it does not try to catch prey exhibiting slow flight, brightly colored wings, and long, thin bodies even though these butterflies are easily caught (Chai, 1996). Young jacamars can learn palatability categories as quickly as adults can (Chai, 1990b)

During other feeding experiments using jacamars and butterflies, male birds were better at discriminating between unpalatable and palatable meals than female birds, although both sexes of jacamars were able to associate color patterns with palatabilities rapidly. Captive jacamars could memorize the color pattern and palatabilities of many different butterflies as well as distinguish between similar Batesian mimics (Chai, 1986).

The flight patterns of butterflies may have evolved as a result of selective pressure from predators. Unpalatable species may advertise their bad taste by flying slowly. Leisurely flights enhance predator associative learning and decrease the number of accidental encounters between butterfly and predator. The divergence of flight patterns between unpalatable and palatable butterfly species defines different forms of defense mechanisms. One defense mechanism is chemical, while the other is evasive flight (Chai et al, 1990b).

Three genra of temperate butterflies were tested for palatability and flight behavior correlations. The experiments used Pieris, Colias, and Pontia as prey for red-winged blackbirds (Agelaius phoeniceus). The position of the centre of body mass was comparable to that of neotropical species. The results showed that the most palatable genus had the center of mass positioned near the wing base, which helps the butterflies avoid being captured. The allocation of body mass to muscle is greatest in the most palatable genus. However, body shape does not correlate. The most palatable genus does not have the shortest abdomen (Srygley et al, 1998).

Unpalatable butterflies do not use evasive flight as part of predator escape mechanisms, thus more mass is designated to other tissues (Marden et al,1991). Butterfly species that display Mullerian mimicry, when many unpalatable or "poisonous" species resemble eachother (Muller, 1878) do not have the need for well-developed flight muscles and evasive flight due to chemical defenses. Butterfly species that are palatable, but resemble unpalatable species in Batesian mimicry (Bates, 1862) do not have the selective pressure to evolve evasive flight and thick flight muscles in the thorax. A high amount of abdominal mass indicates a disproportionate distribution of digestive and reproductive organs. A high amount of thoracic mass indicates a high distribution of muscle mass (Srygley et al, 1990b). In unpalatable butterflies, more body mass is allocated to nonmuscle tissues such as gut and reproductive tissues. Therefore, they can spend more time and energy reproducing. It has been shown that unpalatable species have a greater fecundity than palatable species (Srygley, 1990). Unpalatable female butterflies have larger ovaries, an increased rate of egg production, and increased productivity. Consequently, reproduction is influenced by the predation of butterflies, because unpalatable species have a higher fitness. There is a trade-off between flight muscle tissue and nonflight (particularly reproductive) tissues and is a premise of the Oogenesis-flight syndrome. Because unpalatable butterflies have increased reproductive fitness, it can be assumed that chemical defenses are a benefit. However, sequestering secondary plant compounds by larvae can be costly, and may result in a reduced rate of growth or in death. Therefore, unpalatable butterfly reproductive success may not be superior to the palatable butterfly evasive-flight strategy. Palatable species have increased flight escape ability, but reduced fitness due to a reduced amount of reproductive tissue (Marden et al, 1991).

The most important strategy for evasive flight is well-developed thoracic flight muscles. Fast flying, palatable butterflies have a higher proportion of flight muscle per body mass than slow flying, unpalatable species. However, predictions based on the allocation of flight muscle are hindered by sexual selection. Predictions of palatability based on mass allocation can be misleading in male butterflies. Sexual selection favors a high allocation of body mass to flight muscle in male butterflies due to courtship flights. During courtship, males often find themselves chasing females (Marden et al, 1991). In males, palatability and abdominal mass are negatively correlated. Flight speed correlates positively with thoracic mass in palatable verses unpalatable butterflies (Srygley et al, 1990b). The hypothesis is that protection through evasive flight is not required in unpalatable Mullerian mimics, is partially required in nonmimetic unpalatable and Batesian mimic species, and is necessary in palatable species of butterflies (Marden et al, 1991).

The results of the experiments show that allocation of body mass to specific tissues varies with the palatabilities of butterflies. These experiments suggest that avian predation is the pressure responsible for the selection in unpalatable verses palatable species of butterfly. Mullerian mimetic and unpalatable butterflies do not have to allocate a large amount of mass to flight muscle (Marden et al, 1991).

Large thoracic flight muscles are associated with high metabolic energy costs. Slow flying butterflies have reduced flight muscles in their thorax thus they do not have high-energy requirements related to muscle mass (Chai et al, 1990a).

The energy requirements of butterflies may determine their habitat. The habitat of unpalatable butterflies is not restricted to weather conditions, sunlight, or microhabitat. Palatable butterflies are restricted to sun-filled microhabitats (Chai et al, 1990a). Unpalatable butterflies are active diurnally and occupy closed microhabitat. Palatable butterflies occupy open or very open microhabitats and are active during the midday. Palatable butterflies require a habitat with large amounts of solar radiation and a high ambient temperature. The high thoracic body temperature may be related to the amount of solar radiation absorbed, a higher metabolic heat gain, and a smaller loss of body heat through conduction. Palatable butterflies often bask in the sun, possibly to maintain a higher body temperature. Butterflies with wider thoraxes tend to be palatable as well as have massive flight muscles. These butterflies can fly faster and maneuver with ease, but have restricted habitats and must have sunlight. The larger flight muscles that aid in predator escape, hinder reproduction in these butterflies because they have less mass to allocate to their abdomen for extensive and expensive reproductive tissues. They also have efficient metabolisms to supply the high-energy requirements of large muscles. As a result, thermal specialization may have occurred. The results of experiments using Papilionidae show that flight behavior and palatability are related. Faster species are more palatable (Srygley et al, 1990a).

The body shape, position, and size are related to palatability. The position of the center of mass correlates to flight speed and palatablity. A large thorax and a short abdomen are characteristic of palatable species. The position of the center of mass for a larger thorax is located near the wing base. The model of thoracic diameter and abdominal length can predict the palatability of butterflies (Srygley et al, 1993). Faster fliers with shorter bodies and the abdomen tucked neatly between the two hind wings make it difficult for predators to grab, allowing the butterfly to escape more easily (Chai et al, 1990a).

Unpalatable butterflies have a high wing aspect ratio with longer forewings and shorter wing chords. Palatable butterflies have a low wing aspect ratio with shorter forewings and longer wing chords (Chai et al, 1990a).

All butterflies, even unpalatable butterflies, respond to a disturbance with zigzagging flight patterns and a net movement upward. Aerial predators flight faster but in a horizontal plane. Therefore the butterfly has an advantage in manuverability and can often escape its predator (Marden et al, 1991).

Butterflies escape predators using flight speed and maneuverability. Slow fliers, which are less susceptible to predation, are active in the shade while fast fliers, which are very susceptible to predation, are active only in the light (Wallace, 1865). An increase in flight agility is associated with an increase in thoracic temperature. Palatable species may have to fly faster to avoid predators, and have an increased thoracic temperature. This may influence the microhabitat of both palatable and unpalatable species. Palatable species require bright and sunny microhabitats in order to reach high body temperatures and maximize flight capabilities (Srygley et al, 1990a).

Two selection pressures have been identified for heliconiine butterflies. The pressures include flight speed and predator learning through morphological and behavioral characteristics. The butterflies were grouped into four categories based on their relative palatability to jacamars. The selection pressure on butterflies may change morphologies such as shape or flight speed. Unpalatable butterflies may be selected for shape to be distinguishable by visual predators. Palatable butterflies may be selected for their flight ability in order to escape from predators (Srygley, 1990).

The most important part of predator avoidance in butterflies is being able to escape. Fast flying, palatable butterflies have to have large velocities and good turning radii in order to escape from predators (Howland, 1974). Wing loading and body diameter correlate isometrically in butterflies (Dudley, 1989). Using this model as a predictor, fast flying butterflies with short, stout bodies and massive flight muscles have high wing loading potential.

Associative learning in predators is facilitated by aposematic coloration in prey. In experiments with blue jays (Cyanocitta cristata), pipevine swallowtail butterflies (Battus philenor) that were oriented with their brightly colored wings fully displayed were rejected after only a few encounters. The jays "associated" the wing color patterns with the bad taste of the butterflies (Codella et al, 1990).

The response of a predator (G. ruficauda) to different species of Heliconius was examined. The two species of butterflies are different only in underside wing color. The palatable species has a white underside while the unpalatable species has an orange-red underside. The palatable species was often chased and always consumed during the experiments. The unpalatable species was not chased often, but was never eaten when it was caught. The undersides of the wings were colored with markers, which made all of the butterflies unpalatable, regardless of the coloration. The jacamars were trained to avoid butterflies with certain color patterns. This ability of the predators to learn from one unpalatable butterfly and associate this experience with other butterflies that are the same color may be how mimicry evolved. The results are consistent with birds learning to associate color patterns with palatability (Chai, 1988).

A computer program was tested to see if predator learning is Pavlovian in nature. The palatable mimics were found to act like Batesian mimics (Speed, 1993). The mimics are more successful when they are rare, and tend to show mimetic polymorphism (Turner, 1977). The unpalatable butterflies have two effects. One effect was like Mullerian mimicry where a large numbers of individuals are favored and they show mimetic monomorphism. Mullerian mimics exist in large numbers in order to educate predators about toxicity. Mullerian mimicry is reciprocal and beneficial to all. The other effect is to act like Batesian mimicy, which may have resulted from a gradient of palatablities being presented to the predator (Speed, 1993). Batesian mimicry is one sided, and benefits only the individual. A species that is brightly colored but only slightly unpalatable may cause the predators to doubt earlier bad experiences and sample the population as if all of the species are palatable. This leads to an effect similar to Batesian mimicry (Speed, 1993). In some instances, it may be more profitable for a predator to attack quickly rather than wait and miss an opportunity to attain food. This is where predator learning comes in. If a predator has already learned that a potential food source is unpalatable, then it may not attempt to capture the prey. Conspicuous coloration and slow flight patterns may have evolved as a way to "teach" the predator to be weary of this prey (Guilford, 1986).

Aposematic coloration may not have evolved as a result of warning coloration, but in response to predator selection pressures. Predators can learn to associate bright colors swiftly with bad taste whereas it may take predators longer to associate bad taste with cryptic coloration. Experiments performed with young chicks and chemically treated bread crumbs were found to support this hypothesis (Gittleman et al, 1980).

The next theory describing the evolution of aposematic coloration accounts for coloration and unpalatability together. Coloration and unpalatability may have evolved together coincidentally. A replacement hypothesis is that the coloration evolved because unpalatable animals are highly susceptible to predation (Guilford, 1988).

Another theory illustrates the selection pressure for aposematic coloration as differential predation on brightly colored verses cryptically colored prey. Under this model, an interaction between predator and prey, aposematic animals must not be too detectable, the predator must be capable of learning and memory, and prey density of the prey must be low per predator. This model is not inconsistent with biology (Harvey et al, 1982).

The behavior and habitats of nine different mimetic Heliconius species was recorded. It was found that co-mimics and non-mimics did not fly in the same habitats and roosts in different habitats at night. There was no difference in the flight height between co-mimics and non-mimics (Mallet et al, 1995). Butterfly wing color has not been shown to correlate with butterfly stratisfication in the rainforest. Some butterflies have been shown to have preferences for habitats. Orange and yellow butterflies tend to associate with the canopy while clearwings associate with the forest floor (Burd, 1994). Aposematic colors tend to be transparent, or white, oranges, and reds and/or blacks. Palatable butterflies tend to be brown, yellow, blue or green (Chai, 1986). All of the butterflies flew from the forest floor to the canopy. Although there was no apparent stratisfication of color patterns, mimicry and behavioral ecology have been linked in nine species of Heliconius (Mallet et al, 1995).

Wing beat frequency and asymmetry of wing motion may be a behavioral signal to predators that a meal is unpalatable (Srygley et al, 1999a). Using energetic cost of flight and the flight behavior of two pairs of co-mimics of Heliconius butterflies, reproductive fitness is estimated. The energy costs between the two pairs of co-mimics seems to be equal because one set beats its wings more frequently, while the other set carries a larger body mass. Since the energetic costs are equal, neither species has a higher fitness. The result is two adaptive peaks. Butterflies within each peak have the same reproductive fitness as butterflies in the other peak (Srygley et al, 1999b).

Brower found that locomotor activity, presented by Srygley in 1994, in butterflies does not follow closely with the viewpoints of G.C. Williams (1995). Williams suggests that natural selection is an amazing concept that does occur, but does not occur as often as scientists propose. The term is applied too frequently to explain all morphological variation. It is hypothesized that mutations are more frequently deletarious and not adventitious. Therefore, genes in a population do not change frequently. Williams alludes to other reasons for variation, and believes that evidence should be examined carefully before conclusions of adaptation due to natural selection are made (1966). Locomotor activity in butterflies was not found to be a trait that evolved due to selection pressures from predators because it is not similar enough between clades (Brower, 1995). Mimicry, both Batesian and Mullerian are so poorly understood in the context of selection that it is hard to determined adequate selection pressures from predators in the context of mimicry.

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