Plant Mimicry Evolution of Erroneous Exploitation
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ISSN : 0974 - 7532 Volume 7 Issue 10 Research & Reviews in BBiiooSScciieenncceess Review RRBS, 7(10), 2013 [417-430] ‘ ’: An enthralling Plant mimicry evolution of erroneous exploitation Avani R.Patel, Dhruti H.Mistry* C G Bhakta Institute of Biotechnology, UKA Tarsadia University, Gopal Vidyanagar, Bardoli Mahua Road, Tarsadi, 394350 (INDIA) E-mail: [email protected]; [email protected]; [email protected] ABSTRACT KEYWORDS “mimicry” is racking the brain of scientists, novelists, ecologists, The term Mimicry; evolutionists and lay man readers since this behavior has been observed. Plants; Many plants have evolved to appear like other plants, its own parts, Visual deception. inanimate objects, animals, fungi, or most commonly insects. This can have wide ranging benefits including increasing pollination, protection, and imitation and so on. The present review is a huddle of information about the so called “MIMICRY” in plants viewing grounds of it; predominantly the talk on plants which mimic animals, other plants, inanimate object and fungi. “Ant mimicry”, Further, mimicry has been portrayed in diverse way naming “Aphid mimicry”, “caterpillar mimicry” on the basis of which object is being mimicked by plants. 2013 Trade Science Inc. - INDIA INTRODUCTION characteristics with another group, the models. Cam- ouflage, in which a species resembles its surroundings, It is widely accepted that mimicry evolves as a posi- is essentially a form of visual mimicry. Crypsis is a tive adaptation. The lepidopterist and writer Vladimir broader concept which encompasses all forms of avoid- Nabokov argued that although natural selection might ing detection, such as mimicry, camouflage, hiding etc[4]. “mimic” form, it would not be necessary to stabilize a In any case, the signal always functions to deceive the create it. It may be that much of insect mimicry, includ- receiver by preventing it from correctly identifying the ing the Viceroy/Monarch mimicry, results from similar mimic. In evolutionary terms, this phenomenon is a form self-organizing processes, and thus the tendency for of co-evolution usually involving an evolutionary arms convergence by chance would be high[1]. race[4]. It should not be confused with convergent In evolutionary biology, mimicry is the similarity of ev o l u t i o n h t t p : / / en . w i k i p e d i a. o rg/ w i k i / one species to another which protects one or both[2]. Convergent_evolution, which occurs when species This similarity can be in appearance, behaviour, sound, come to resemble one another independently by adapt- scent and location, with the mimics found in similar places ing to similar lifestyles. to their models[3]. Mimicry occurs when a group of or- Mimics may have different models for different life ganisms, the mimics, evolve to share common perceived cycle stages, or they may be polymorphic, with differ- ‘ ’ 418 Plant mimicry : An enthralling e.volution of erroneous exploitation RRBS, 7(10) 2013 Review ent individuals imitating different models. Models them- of various types helps in plant defense. More specifi- üllerian mimicry was already proposed to exist selves may have more than one mimic, though frequency cally, M dependent selection favors mimicry where models out- in several defensive plant signaling systems. The first number mimics. Models tend to be relatively closely was for several spiny species with white-variegated related organisms[4], but mimicry of vastly different spe- leaves[23,27,28]. The second was for some tree species cies is also known. Most known mimics are insects[3], with red or yellow poisonous autumn leaves[29]. The üllerian and Batesian though many other animal mimics including mammals third cases are of a mixture of M are known. Plants and fungi may also be mimics, though mimicry, of thorn automimicry found in many Agave less research has been carried out in this area[5-7]. species[27]. The most widely accepted model used to explain Aposematic (warning) coloration is a biological phe- the evolution of mimicry in butterflies is the two-step nomenon in which poisonous, dangerous or otherwise hypothesis. In this model the first step involves muta- unpalatable organisms visually advertise these qualities tion in modifier genes that regulate a complex cluster of to other animals. The evolution of aposematic colora- linked genes associated with large changes in morphol- tion is based on the ability of target enemies to associ- ogy. The second step consists of selections on genes ate the visual signal with the risk, damage or non-prof- with smaller phenotypic effects and this leading to in- itable handling, and later to avoid such organisms as creasing closeness of resemblance. This model is sup- prey. Typical colors of aposematic animals are yellow, ported by empirical evidence that suggests that there orange, red, purple, black, white or brown and combi- are only a few single point mutations that cause large nations of these[13,30-33]. phenotypic effects while there are numerous others that Many thorny, spiny and prickly plant species were produce smaller effects. Some regulatory elements are proposed to be aposematic because their sharp defen- now known to be involved in a supergene that is in- sive structures are usually colorful (yellow, orange, red, volved in the development of butterfly color patterns. brown, black, white) and/or associated with similar Computational simulations of population genetics have conspicuous coloration[13,27,28,34-47]. also supported this idea[8]. The mechanisms involved in plant deception, with Species resemble each other owing to a shared phy- an emphasis on pollination has been reviewed[48]. They logenetic history or adaptation to a similar abiotic or proposed that generalized food deception evolves if biotic environment. Among the various adaptations that plants exploit the innate preferences of pollinators, and plants show, deception of other organisms is arguably thus represents a form of exploitation of perceptual bi- one of the most intriguing. Traditionally, mimicry has ases (EPB). They contrast this with floral mimicry, which been the primary concept put forward to explain de- is viewed as a distinct phenomenon that might originate ception. The mimicry hypothesis rests upon the princi- with EPB before selection hones the resemblance be- pal assumptions that the model (species that is imitated) tween a mimic and a specific model. They argued that and the mimic (species imitating the model) interact with EPB in the form of pre-existing bias is not limited to the same receiver individuals, that the receiver mistakes deceptive plants, but rather drives the evolution of flo- one for the other, and that this mistake has important ral traits of animal-pollinated plants in general. Further, fitness consequences for the mimic and, often, also for in their view, EPB is central to the evolution of floral the model[9-13]. mimicry, which differs from generalized mimicry only in Plant community ecology offers tools to study flo- the exploitation of specialized pollinators, leading to a ral colours. For example, the influence of floral colour close resemblance between mimics and specific mod- as a driving force of evolution was addressed[14], who els. Schaefer and Ruxton highlighted the importance of evaluated colour distribution within plant communities. preexisting biases in pollination through the EPB model. They discovered that rare plants tended to be more They agreed that EPB is an important mechanism for distinguishable from the rest of the community than com- understanding the evolution of floral traits, but suggested mon plants by hymenopteran pollinators, and this would that it is more widely applicable to floral evolution, and help to secure pollination. that it cannot explain the evolution of deceptive flow- Several authors[15-26] have proposed that mimicry ers. The prerequisites for EPB to select for particular RRBS, 7(10) 2013 Avani R.Patel and Dhruti H.Mistry 419 Review plant signals are: (1) pollinators having specific innate plants[56]. Proximate mechanisms of floral trait evolu- preferences; (2) plants being limited in their reproduc- tion may not differ appreciably between rewarding and tive success by access to pollinators (i.e. increased deceptive plants. The key to understanding deception pollinator attraction increases plant fitness); and (3) in- in plants can be found among the ultimate reasons driv- sect perceptual systems predating plant signals, thus the ing the evolution of nectar-less flowers. A seeming para- evolution of plant signals exploits pre-existing sensory dox in deceptive plants is that experimental addition of preferences in the pollinators. There is ample evidence a reward usually leads to a strong increase in gross for all three conditions across plant and pollinator lin- pollination success, making deception appear maladap- eages. Several studies have shown that plants are often tive[57]. However, pollinators also tend to move between pollinator-limited in their reproductive success[49]. plants more often if flowers are deceptive, thus increasing Phylogenetically informed approaches to the evo- the rate of outcrossing[57]. Deception may thus repre- lution of sensory systems in insects and the correspond- sent one of the many plant strategies that reduce in- ing signals in plants indicate that insect vision and olfac- breeding. tory systems predated the evolution of floral colour and scent in angiosperms[50,51]. Examples of floral signals PLANTS THAT MIMIC ANIMALS influenced by preexisting pollinator bias include the con- vergent evolution of red colouration in bird-pollinated Orchid and bee flowers, which may result from better detection of the Through pseudoantagonism, Orchids exploit the ter- colour red in birds, possibly because red serves as an ritorial behavior of some Hymenoptera, which attack [52] intra-specific communication signal in birds . Floral the flowers when they are vibrating in the wind and pol- guides (stripes, dots) might have evolved under innate linate them in the process. The defensive behaviour of preferences of bees for radiating stripes, dark centres, territorial bees (Centris spp.) may be exploited by some [53] and peripheral dots .