Mullerian mimicry

Two speculative possibilities relate to olfactory aposematism. The first is whether there are non-toxic plants that smell or taste like toxic ones. In other words, do plants practice Batesian mimicry. Such mimicry is unlikely, as mammalian herbivores constantly sample plants and thereby test for favorable and adverse effects of eating a particular species. Furthermore, given the keen sense of smell of mammals, two plant species would have to exactly smell alike for mimicry to work. Second, do two distasteful or toxic plant species smell or taste alike so that herbivores can more easily classify dangerous plants and avoid them (Mullerian mimicry) (Eisner and Grant, 1981 Lindroth, 1988 Augner and Bernays, 1998). 

The members of the family Arctiidae, which numbers over 11 000 species, are often brilliantly colored (Watson and Goodger, 1986 Holloway, 1988 Weller etal, 2000a). In addition to standard aposematic red, yellow, or black patterns, adults and larvae may have iridescent blue and green, or even pearly white, coloration. White can be considered aposematic when individuals rest conspicuously on green vegetation. Numerous species are involved in mimicry rings with other distasteful species. Many adults are superb Mullerian mimics of lycid beetles, bees, wasps,... 

Rothschild, M. (1961). Defensive odours and Mullerian mimicry among insects. Transactions of the Royal Entomological Society of London 113 101-113. 

Mullerian mimicry— A type of mimicry in which two or more species evolve toward a similar appearance so that learned avoidance by a predator will result in fewer deaths for any given species. 

Likewise, parapatric polymorphism (subspecies) should not be expected in Mullerian mimicry. This is not so much because of forces opposing it as from a lack of forces creating it. The existence therefore, of several geographically variable Mullerian rings is puzzling in terms of classical mimicry theory (see Section 10.5). 

Much less experimental work has been done on Mullerian mimicry than on Batesian mimicry. Thus feeding experiments have been few. Benson (1972) was able to establish natural selection operating to stabilize the mimetic pattern of Heliconius erato in Costa Rica by comparing survival times and wing damage in altered non-mimics versus controls. 

The Batesian and Mullerian forms of mimicry are not the only ones known (see Section 10.6), but they are the best defined and have more quantitative data... 

Table 10.1 Comparison of attributes of traditional Mullerian and Batesian mimicry...

Because of the advent of data and the desire to predict and to model mimetic systems, the past two decades have seen a number of attempts to construct mathematical models, often utilizing the simulative power of the computer. Thus Huheey (1964, 1976) has presented models for Batesian and Mullerian mimicry, respectively, based originally on the experimental data of J. Brower (1960) with respect to the feeding habits of starlings on quinine-dipped mealworms, but augmented by data on the reaction of toads and treefrogs to honeybees, Apis mellifera (Huheey, 1980b). Other workers who have made valuable... 

Traditionally, the concepts of Batesian and Mullerian mimicry have been considered completely distinct. Certainly, this seems true in many of the factors operating and in the predictions that one would make on the basis of Table 10.1. Therefore most students of mimicry have tended to view Batesian and Mullerian mimicry as discrete, isolated compartments. Some have gone so far as to say that mimicry is Batesian mimicry, that Mtillerian mimicry is merely warning coloration, and the two should not even be considered at the same time. As we shall see, this will not be the only time that semantics raises its head. Still, vexing questions continue to be posed. One is the very problem of the evolution of mimicry which, needs be, raises further questions concerning how species cross over the absolute boundaries of crypsis/aposematism or pseud-aposematism/aposematism (see Section 10.7). 

Despite the apparently discrete characters of Batesian and Mullerian mimicry, many authors (Fisher, 1958 Huheey, 1961 Linsley et al., 1961 Eisner et al., 1962 L. Brower and J. Brower, 1964 L. Brower et al., 1970 Pougheta/., 1973 Huheey, 1976 Brandon eta/., 1979 Sbordoni eta/., 1979) have discussed, from either an empirical or theoretical viewpoint, apparent intermediate cases between classical Batesian and Mullerian mimicry or the evolution of Batesian mimicry into Mullerian mimicry, or vice versa. 

An interesting example is provided by certain lycid and cerambycid beetles. The lycids are unpalatable to vertebrates, warningly colored, and mimicked by palatable cerambycids. The situation would thus seem to be simply one of Batesian mimicry, but the cerambycids are carnivorous We thus have the unusual situation of the Batesian mimic preying upon its model, thereby ingesting the model s toxin, and presumably in turn becoming toxic - a Mullerian mimic ... 

A third species, H. doris presents further problems for the notion that Bate-sian and Mullerian mimicry form neat pigeonholes. Although it is unpalatable, L. Brower et al. (1963) found that it is the least so of the five species tested. Complementing this weak deterrent, H. doris is polymorphic, mimicking two aposematic patterns of other members of the genus, and has a third, apparently non-mimetic, morph. Thus, as a weak Mflllerian mimic, H. doris has evolved in ways typical of a classical Batesian mimic (Huheey, 1976 1980c). 

Such Batesian-Mtillerian mimicry problems are not limited to the butterflies. Dressier (1979) describes Mullerian rings of bees Eulaema spp. and Euplusia spp.), yet admits, Though the mimetic relationships between Euplusia and Eulaema are Mtillerian, in most cases I consider Eulaema to be the model, and Euplusia the mimic . He goes on to list other similar species, and the reasons for his conclusions. 

Rothschild (1961,1964) lists several cases of odor mimicry, both Mullerian and Batesian. This raises an interesting question If a Batesian mimic develops both a noxious odor and taste that furthers the resemblance to the model (Batesian mimicry), has it not built the first of multiple-lines-of-defense and thus become an incipient Mullerian mimic ... 

This category is not exclusive of the others inasmuch as it involves visual, olfactory, or auditory perceptions by the predator. The emphasis here, however, is upon behavioral patterns that lead to deception of the predator. That a Mullerian and Batesian mimic should adapt in such a way as to resemble its model in as many ways as possible is to be expected, but mimicry has gone beyond such simple one-to-one comparisons. 

There are further examples of similar chemical mimicry such as in termito-philes (Howard et al., 1980) and myrmecophilous beetles (Vander Meer and Wojcik, 1982), but at this point Mullerian chemical mimicry merges imperceptibly with a general study of interspecific pheromones and is out of place in this review. 

Another method for the evolution of Mullerian mimicry has been suggested. In a sense, a Batesian mimic is pre-adapted for evolution towards Mullerian mimicry. Furthermore, we have seen adjustments in the behavior of predators after being exposed to unpalatable prey They attack more slowly and cautiously, and sometimes taste but fail to maintain the attack (J. Brower, 1958,1960). Mimetic prey is thus not exposed to as severe attack as a non-mimic (until the sham is pierced). It would be more likely to survive and continue its evolution towards Mullerian mimicry if some incipient offensive distastefulness was developed (Huheey, 1961). It has been suggested that this is the only means available for the initiation of Mullerian mimicry in rare species (L. Brower et al., 1970). The conditions favoring the evolution of a Batesian mimic into a Mullerian mimic have been determined from the mathematical model and are not surprising The model must not be overly abundant nor have a strong protective deterrent. In other words, if the Batesian mimicry is weak, it behooves the mimic to evolve its own deterrent (Huheey, 1976). 

Benson, W. W. (1972) Natural selection for Mullerian mimicry in Heliconius erato in Costa Rica. Science, 176, 936-9. 

Benson, W. W. (1977) On the supposed spectrum between Batesian and Mullerian mimicry. Evolution, 31, 454-5. 

Brower, L. P., Brower, J. V. Z. and Collins, C. T. (1963) Experimental studies of mimicry. 7. Relative palatability and Mullerian mimicry among Neoptropical butterflies of the subfamily Heliconiinae. Zoologica, 48, 65-84. 

Brown, Jr., K. S. and Benson, W. W. (1974) Adaptive polymorphism associated with multiple Mullerian mimicry in Heliconius numata (Lepid. Nymph.). Biotropica, 6, 205-28. 

Dressier, R. L. (1979) Eulaema bombiformis, E. meriana, and Mullerian mimicry in related species (Hymenoptera Apidae). Biotropica, 11, 144-51. 

Huheey, J. E. (1961) Studies in warning coloration and mimicry. III. Evolution of Mullerian mimicry. Evolution, 15, 567-8. 

Huheey, J. E. (1980c) Batesian and Mullerian mimicry Semantic and substantive differences of opinion. Evolution, 34, 1212-15. 

Mimicry in the burnet moth Zygaena ephialtes Population studies and evidence of a Batesian-Mullerian stiuation. Ecol. Ent, 4, 83-94. 

Turner, J. R. G. (1976a) Mullerian mimicry classical beanbag evolution and the role of ecological islands in adaptive race formation. In Population Genetics and Ecology (Karlin, S. and Nevo, E., eds) pp. 185-218. Academic Press, New York. 

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