The protective value of conspicuous signals is not impaired by shape, size, or position asymmetry

The protective value of conspicuous signals is not impaired by shape, size, or position asymmetry

Behavioral Ecology (2009) Vol. 20, No. 1, 96-102
Martin Stevens, Sarah A. Castor-Perry, and Jessica R.F. Price
Department of Zoology, University of Cambridge

Various conspicuous signals in nature promote initial and learned avoidance by predators. It is widely thought that such signals are most effective when highly symmetrical in features such as size and shape, supported by recent laboratory experiments with domestic chicks and artificial prey. However, no study has investigated the effect of asymmetry on conspicuous signals in a natural setting, where viewing distances, angles, predator species, and light conditions vary and where predators encounter prey sequentially rather than simultaneously. We undertook 2 field experiments with artificial gray-scale prey, marked with a pair of white markings presented to wild avian predators, to test the effect of asymmetry on the survival value of conspicuous signals in the field. Experiment 1 had treatments with symmetrical spots or with spots asymmetrical in area between 5 and 50%. All marked
treatments survived better than unmarked controls, but there was no benefit of being symmetrical. Experiment 2 tested the effect of possessing markings asymmetrical for shape or position and any additive effect of these 2 features. Again, symmetry conferred no benefit and targets with markings asymmetrical for position and/or shape survived equally well as those with symmetrical arrangements. These findings indicate that asymmetry in warning signals may not be costly to prey in nature or be of less importance compared with other features of the signal, such as color and overall size.

Keywords: antipredator coloration, aposematism, birds, eyespots, predation, symmetry.

Testing the predatory behaviour of Podarcis sicula (Reptilia: Lacertidae) towards aposematic and non-aposematic preys

Bonacci, Teresa, Gaetano Aloise, Pietro Brandmayr, Tullia Z. Brandmayr and Massimo Capula. 2008. Testing the predatory behaviour of Podarcis sicula (Reptilia: Lacertidae) towards aposematic and non-aposematic preys. Amphibia- Reptilia. 29 (3): 449-453. [t.bonacci@unical.it]

Abstract: Food preferences and the effects of prey chemical repellents in the dietary behaviour of Podarcis sicula were tested using four species of Carabid beetles as prey models. The goal of the study was to assess (i) the ability of P. sicula to recognize insect preys provided with chemical repellents and aposematic colorations under laboratory conditions, and (ii) the importance of chemical signals used by the prey model as antipredatory strategy. Preys used in this study were Brachinus sclopeta and Anchomenus dorsalis (aposematic species) and Amara anthobia and A. aenea (non-aposematic species). Aposematic species are characterized by warning color pattern and by production of chemical repellents, while non-aposematic ones do not. Amara anthobia and A. aenea were attacked with high frequency by P. sicula, Brachinus sclopeta and Anchomenus dorsalis with low frequency. Non-aposematic species were preyed more often than the aposematic ones. Brachinus sclopeta was preyed after low latency, while Amara anthobia and A. aenea after long latency. Non-aposematic species were captured and eaten without difficulty, while when B. sclopeta or A. dorsalis were captured, lizards always tossed their head and then rub the snout on the soil, probably because of the unpalatability of aposematic preys.

Optimal-Foraging Predator Favors Commensalistic Batesian Mimicry

Optimal-Foraging Predator Favors Commensalistic Batesian Mimicry

Atsushi Honma1¤*, Koh-ichi Takakura2, Takayoshi Nishida1

1 Laboratory of Insect Ecology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan, 2 Osaka City Institute of Public Health and Environmental Science, Osaka, Japan

Background

Mimicry, in which one prey species (the Mimic) imitates the aposematic signals of another prey (the Model) to deceive their predators, has attracted the general interest of evolutionary biologists. Predator psychology, especially how the predator learns and forgets, has recently been recognized as an important factor in a predator–prey system. This idea is supported by both theoretical and experimental evidence, but is also the source of a good deal of controversy because of its novel prediction that in a Model/Mimic relationship even a moderately unpalatable Mimic increases the risk of the Model (quasi-Batesian mimicry).

Methodology/Principal Findings

We developed a psychology-based Monte Carlo model simulation of mimicry that incorporates a “Pavlovian” predator that practices an optimal foraging strategy, and examined how various ecological and psychological factors affect the relationships between a Model prey species and its Mimic. The behavior of the predator in our model is consistent with that reported by experimental studies, but our simulation's predictions differed markedly from those of previous models of mimicry because a more abundant Mimic did not increase the predation risk of the Model when alternative prey were abundant. Moreover, a quasi-Batesian relationship emerges only when no or very few alternative prey items were available. Therefore, the availability of alternative prey rather than the precise method of predator learning critically determines the relationship between Model and Mimic. Moreover, the predation risk to the Model and Mimic is determined by the absolute density of the Model rather than by its density relative to that of the Mimic.

Conclusions/Significance

Although these predictions are counterintuitive, they can explain various kinds of data that have been offered in support of competitive theories. Our model results suggest that to understand mimicry in nature it is important to consider the likely presence of alternative prey and the possibility that predation pressure is not constant.

[Article]Being conspicuous and defended: selective benefits for the individual

Being conspicuous and defended: selective benefits for the individual

Christina G. Halpin, John Skelhorn and Candy Rowe

Centre for Behaviour and Evolution, Institute of Neuroscience, Newcastle University, Henry Wellcome Building, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK

Aposematic insects conspicuously advertise their unprofitability to potential predators. However, when these prey initially evolved, they were likely to have been rare and presumably at a greater risk of being detected and killed by naive predators. Both kin and individual selection theories have been used in attempts to explain this apparent paradox, with much of the empirical research supporting kin selection–based theories. Here, we experimentally test how chemical defence levels in prey and avian color biases influence the probability of a rare conspicuous morph having an initial survival advantage. We used newly hatched domestic chicks (Gallus gallus domesticus) foraging on green and purple prey, on a green or purple background, to model the evolutionary scenario of a rare conspicuous morph arising in a population of already defended cryptic prey. Defended prey were produced by spraying them with quinine solution, which the birds readily detect and can learn to avoid. Although attack rates were initially similar for both defended prey types, the chicks only learned to avoid defended prey when they were conspicuous, not when they were cryptic. In addition, defended conspicuous prey were more likely to be rejected on attack than defended cryptic prey, even when first encountered by a predator. These data suggest that there could be a selective advantage for a rare conspicuous morph to arise in a population of cryptic defended prey due to increased avoidance learning and taste-rejection in naive predators. Our findings also suggest that being a non-preferred color and/or highly defended will increase the probability of this evolutionary scenario.

keywords: aposematism, avoidance learning, color bias, predation, receiver psychology, taste-rejection, warning signal.

[Article]Dazzle coloration and prey movement

Dazzle coloration and prey movement

Martin Stevens1, Daniella H. Yule1, Graeme D. Ruxton2

1Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK
2Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK

Many traits in animals reduce the rate of attack from visually hunting predators, including camouflage, warning signals and mimicry. In addition, some animal markings may reduce the likelihood that an attack ends in successful capture. These might include dazzle markings, high-contrast patterns that make the estimation of speed and trajectory difficult. However, until now, no study has experimentally tested whether some markings may achieve such an effect. We developed a computer ‘game’ where human ‘predators’ have to capture computer-generated prey moving across a background. In two experiments, we find that although uniform camouflaged targets were among the hardest to capture, so were a range of high-contrast conspicuous patterns, such as bands and zigzags. Prey were also more difficult to capture against more heterogeneous than uniform backgrounds, and at faster speeds of movement. As such, we find the first experimental evidence that conspicuous patterns, similar to those found in a wide range of real animals, make the capture of moving prey more challenging. Various anti-predator markings may work prey during motion, and some animals may combine such dazzle patterns with other functions, such as camouflage, thermoregulation, sexual and warning signals.

keywords: protective coloration, motion, conspicuousness, vision, predation, dazzle

[Artical]Can't tell the caterpillars from the trees: countershading enhances survival in a woodland

Can't tell the caterpillars from the trees: countershading enhances survival in a woodland

Hannah M. Rowland1, Innes C. Cuthill2, Ian F. Harvey1, Michael P. Speed1, Graeme D. Ruxton3

1 School of Biological Sciences, University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK
2 School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
3Division of Environmental and Evolutionary Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Graham Kerr Building, Glasgow G12 8QQ, UK

Perception of the body's outline and three-dimensional shape arises from visual cues such as shading, contour, perspective and texture. When a uniformly coloured prey animal is illuminated from above by sunlight, a shadow may be cast on the body, generating a brightness contrast between the dorsal and ventral surfaces. For animals such as caterpillars, which live among flat leaves, a difference in reflectance over the body surface may degrade the degree of background matching and provide cues to shape from shading. This may make otherwise cryptic prey more conspicuous to visually hunting predators. Cryptically coloured prey are expected to match their substrate in colour, pattern and texture (though disruptive patterning is an exception), but they may also abolish self-shadowing and therefore either reduce shape cues or maintain their degree of background matching through countershading: a gradation of pigment on the body of an animal so that the surface closest to illumination is darker. In this study, we report the results from a series of field experiments where artificial prey resembling lepidopteran larvae were presented on the upper surfaces of beech tree branches so that they could be viewed by free-living birds. We demonstrate that countershading is superior to uniform coloration in terms of reducing attack by free-living predators. This result persisted even when we fixed prey to the underside of branches, simulating the resting position of many tree-living caterpillars. Our experiments provide the first demonstration, in an ecologically valid visual context, that shadowing on bodies (such as lepidopteran larvae) provides cues that visually hunting predators use to detect potential prey species, and that countershading counterbalances shadowing to enhance cryptic protection.

keywords: countershading, crypsis, predation, animal coloration, defensive coloration

[Article]Learning and the mimicry spectrum: from quasi-Bates to super-Müller

Learning and the mimicry spectrum: from quasi-Bates to super-Müller

Alexandra C.V. Balogh^{, a,} , Gabriella Gamberale-Stille^a and Olof Leimar^a

^aDepartment of Zoology, Stockholm University, Sweden

Müllerian mimicry is the mutualistic resemblance between two defended species, while Batesian mimicry is the parasitic resemblance between a palatable species (the mimic) and an unpalatable one (the model). These two kinds of mimicry are traditionally seen as extreme ends of a mimicry spectrum. For the range in between, it has been suggested that mimetic relations between unequally defended species could be parasitic, and this phenomenon has been referred to as quasi-Batesian mimicry. Where a mimetic relation is placed along the mimicry spectrum depends on the assumptions made about predator learning. We used a variant of the Rescorla–Wagner learning model for virtual predators to analyse the different possible components of the mimicry spectrum. Our model entails that the rate of associative learning is influenced by variation in the stimuli to be learned. Variable stimuli, that is, unequal defences, can increase the predator learning rate and thus lead to an increased level of mutualism in a mimetic relation. In our analysis, we made use of the concepts of super-Müllerian mimicry, where the benefit of mimicry is even greater than in traditional Müllerian mimicry, and quasi-Müllerian mimicry, where mimicry by a palatable mimic is mutualistic. We suggest that these types of mimicry should be included in the mimicry spectrum along with Müllerian, Batesian and quasi-Batesian mimicry.

Keywords: associative learning; mutualism; Müllerian mimicry; quasi-Batesian mimicry; Rescorla–Wagner model

[Article]Multimodal warning signals for a multiple predator world

Nature 455, 96-99 (4 September 2008) | doi:10.1038/nature07087; Received 10 February 2008; Accepted 14 May 2008

Multimodal warning signals for a multiple predator world

John M. Ratcliffe^1,3 & Marie L. Nydam^2,3

1. Center for Sound Communication, Institute of Biology, University of Southern Denmark, DK-5230 Odense M, Denmark
2. Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA
3. These authors contributed equally to this work.

Correspondence to: John M. Ratcliffe^1,3Marie L. Nydam^2,3 Correspondence and requests for materials should be addressed to M.L.N. (Email: mln32@cornell.edu) or J.M.R. (Email: jmr@biology.sdu.dk).

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Abstract

Aposematism is an anti-predator defence, dependent on a predator's ability to associate unprofitable prey with a prey-borne signal¹. Multimodal signals should vary in efficacy according to the sensory systems of different predators; however, until now, the impact of multiple predator classes on the evolution of these signals had not been investigated^{2, 3}. Here, using a community-level molecular phylogeny to generate phylogenetically independent contrasts, we show that warning signals of tiger moths vary according to the seasonal and daily activity patterns of birds and bats—predators with divergent sensory capacities. Many tiger moths advertise chemical defence^{4, 5} using conspicuous colouration and/or ultrasonic clicks^{3, 6}. During spring, when birds are active and bats less so, we found that tiger moths did not produce ultrasonic clicks. Throughout both spring and summer, tiger moths most active during the day were visually conspicuous. Those species emerging later in the season produced ultrasonic clicks; those that were most nocturnal were visually cryptic. Our results indicate that selective pressures from multiple predator classes have distinct roles in the evolution of multimodal warning displays now effective against a single predator class. We also suggest that the evolution of acoustic warning signals may lack the theoretical difficulties associated with the origination of conspicuous colouration.

[Article]Mimetic butterflies support Wallace's model of sexual dimorphism

Mimetic butterflies support Wallace's model of sexual dimorphism
Proc Biol Sci. 2008 Jul 22;275(1643):1617-24.
Krushnamegh Kunte

Section of Integrative Biology, University of Texas at Austin, 1 University Station C 0930, Austin, TX 78712-0253, USA Theoretical and empirical observations generally support Darwin's view that sexual dimorphism evolves due to sexual selection on, and deviation in, exaggerated male traits. Wallace presented a radical alternative, which is largely untested, that sexual dimorphism results from naturally selected deviation in protective female coloration. This leads to the prediction that deviation in female rather than male phenotype causes sexual dimorphism. Here I test Wallace's model of sexual dimorphism by tracing the evolutionary history of Batesian mimicry—an example of naturally selected protective coloration—on a molecular phylogeny of Papilio butterflies. I show that sexual dimorphism in Papilio is significantly correlated with both female-limited Batesian mimicry, where females are mimetic and males are non-mimetic, and with the deviation of female wing colour patterns from the ancestral patterns conserved in males. Thus, Wallace's model largely explains sexual dimorphism in Papilio. This finding, along with indirect support from recent studies on birds and lizards, suggests that Wallace's model may be more widely useful in explaining sexual dimorphism. These results also highlight the contribution of naturally selected female traits in driving phenotypic divergence between species, instead of merely facilitating the divergence in male sexual traits as described by Darwin's model.
Keywords
Batesian mimicry, polymorphism, female-limited mimicry, directional selection, stabilizing sexual selection, convergence

[Article]The role of eyespots as anti-predator mechanisms, principally demonstrated in the Lepidoptera

Review Article The role of eyespots as anti-predator mechanisms, principally demonstrated in the Lepidoptera
Martin Stevens a1 a1 Ecology of Vision, School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG. UK (E-mail: Martin.Stevens@bristol.ac.uk)

Abstract

Eyespots are found in a variety of animals, in particular lepidopterans. The role of eyespots as antipredator mechanisms has been discussed since the 19th Century, with two main hypotheses invoked to explain their occurrence. The first is that large, centrally located eyespots intimidate predators by resembling the eyes of the predators' own enemies; the second, though not necessarily conflicting, hypothesis is that small, peripherally located eyespots function as markers to deflect the attacks of predators to non-vital regions of the body. A third possibility is also proposed; that eyespots intimidate predators merely because they are novel or rarely encountered salient features. These hypotheses are reviewed, with special reference given to avian predators, since these are likely to be the principal visually hunting predators of the lepidopterans considered. Also highlighted is the necessity to consider the potential influence of sexual selection on lepidopteran wing patterns, and the genetics and development of eyespot formation.

Key Words: eyespots; receiver psychology; antipredator signals; Lepidoptera; deflection; startle displays; false-head; visual signals; colour patterns.

[Debate]珊瑚蛇與奶蛇擬態經典案例的諸多疑點

Milk snake與Coral snake所形成的putative mimicry complex成為擬態生物學研究的經典已達一世紀之久. 但是這個擬態群一直存在著兩個違背Batesian mimicry預測的基本問題: (1) 被認為是mimic的奶蛇數量遠比被認為是model的coral snake為多; (2) 兩者不一定(而且經常)是不共棲的. 針對model與mimic不一定共棲的問題, 已經有"allopatric mimicry"這個理論所討論, 對於兩者個相對豐度的問題則應追溯至Brower & Brower (1962)以及Greene & McDiarmid (1981)的文章. Harper & Pfennig (2008)的文章則以族群遺傳學的方法證實了身為mimic的milk snake雄性會進行遷徙, 而且遷徙到coral snake不存在的地區, 間接地提供allopatric mimicry存在的族群遺傳學事證. 然而倒底是什麼記憶力, 學習能力與辯識力好的predator讓allopatric mimicry能夠存在, 則應該是下一個研究的目標.

• Brattstrom, B.H. 1955. The Coral Snake 'Mimic' Problem and Protective Coloration. Evolution 9(2): 217-219.
• Dunn, E.R. 1949. Relative Abundance of Some Panamanian Snakes. Ecology 30(1): 39-57.
• Brower, L. P. & Brower, J. V. Z. 1962. The relative abundance of model and mimic butterflies in natural populations of the Battus philenor mimicry complex. Ecology 43: 154–158.
• Clarke, C. & Sheppard, P. M. 1975. The genetics of the mimetic butterfly Hypolimnas bolina (L.). Phil. Trans. R. Soc. B 272: 229–265.
• Greene, H. W. & McDiarmid, R. Y. 1981. Coral snake mimicry: does it occur? Science 213: 1207–1212.
• Harper, G.R., Pfennig, D.W. 2008. Selection overrides gene flow to break down maladaptive mimicry. Nature 451: 1103-1106.
• Pfennig, D. W., Harcombe, W. R. & Pfennig, K. S. 2001. Frequency-dependent Batesian mimicry. Nature 410: 323.
• Ruxton, G. D., Sherratt, T. N. & Speed, M. P. 2004. Avoiding Attack: The Evolutionary Ecology of Crypsis, Warning Signals and Mimicry. Oxford Univ. Press, Oxford.
• Waldbauer, G. P. & Sternburg, J. G. 1987. Experimental field demonstration that two aposematic butterfly color patterns do not confer protection against birds in Northern Michigan. Am. Midl. Nat. 118: 145–152.
• Wallace, A. R. 1870. Contributions to the Theory of Natural Selection, Macmillan, London.

其它以奶蛇/珊瑚蛇所形成的擬態群為研究的文章可見David W. Pfennig研究群的著作目錄.

[Practice]變色龍適合拿來當成predator嗎?

今天以台灣茶斑蛾(Eterusia taiwana)當成prey, 丟給高冠變色龍, 日守宮和攀蜥試試, 原本的想像是--高冠會因為吃到可怕的東西而生氣變色, 這樣我們就知道高冠是否覺得那個東西unpalatable, 這樣不是很棒嗎? 結果丟了斑蛾給四隻高冠, 四隻看了兩眼, 連試也不試, 就走了, 是因為不餓嗎? NO! 丟蟋蟀下去馬上就被吃掉了, 因此那四隻高冠並不是因為不餓才不吃的啊. 接下來再試一次, 仍然只觀察, 但完全不予理會. 所以使用高冠變色龍做為predation test中的naive predator的夢想破碎.

接下來使用的是日守宮. 日守宮看見斑蛾後會馬上下來咬, 但咬完就放開. 看起來是好的開始. 接下來使用攀蜥也有一樣的效果. 但是馬上再拿給同一隻日守宮再試一次, 牠又咬了一次, 然後又放開沒吃. 這代表什麼呢? 表示這個stimulus的強度不足? 不足以讓日守宮產生警戒? 還是第一次的取食失敗並沒有伴隨明顯的視覺警訊 (那隻斑蛾是羽化失敗的 大多數翅紋沒有顯示)? 或者是日守宮的記憶力不好? 之後我們又試了瑤山鱷蜥, 一樣是咬了後馬上吐出來. 因此日行性的斑蛾對日行性的蜥蜴是unpalatable是確認的. 然而這些蜥蜴是否能夠成為predator test裏的naive predator則需要更多的測試.

[Article: Crypsis]Adaptive evolution of Timema according to hostplants

Adaptive evolution of cryptic coloration: the shape of host plants and dorsal stripes in Timema walking-sticks

• CRISTINA P. SANDOVAL¹*¹Marine Science Institute, University of California, Santa Barbara, CA 93106, USA*E-mail: sandoval@lifesci.ucsb.edu and
• BERNARD J. CRESPI²²Behavioural Ecology Research Group, Department of Biosciences, Simon Fraser University, Burnaby, B. C. V5A 1S6, Canada

• ¹Marine Science Institute, University of California, Santa Barbara, CA 93106, USA
  ²Behavioural Ecology Research Group, Department of Biosciences, Simon Fraser University, Burnaby, B. C. V5A 1S6, Canada

*E-mail: sandoval@lifesci.ucsb.edu

Abstract

The adaptive significance of cryptic colour patterns has seldom been analysed in a phylogenetic context. We mapped data on the presence vs. absence of dorsal stripes, and the use of needle-like vs. broad foliage, onto a recent phylogeny of Timema walking-sticks, in order to infer the evolutionary history of these traits and test the hypothesis that the dorsal stripe is an adaptation for crypsis on needle-like leaves. By maximum parsimony optimization, the dorsal stripe has evolved five or six times in this clade, each time in association with the use of vegetation with needle-like leaves. Maddison's concentrated changes test showed that this association between morphology and habitat was statistically significant. By contrast, results based on Pagel's maximum likelihood analyses did not reach significance, probably because the large number of origins of dorsal stripe introduces statistical uncertainty. These results suggest that the adaptations for crypsis can arise readily and in parallel, in the appropriate selective environment. However, they may also constrain the evolution of host-plant use, as there is no unambiguous case of Timema species with dorsal stripes shifting to broad-leaved plants. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 1–5.

See another paper published by Sandoval

[Article: Floral mimicry]Chemical mimicry as a preadaptation

Evolution of sexual mimicry in the orchid subtribe orchidinae: the role of preadaptations in the attraction of male bees as pollinators

Florian P Schiestl¹ and Salvatore Cozzolino²

¹Institute of Systematic Botany, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland

²Università degli Studi di Napoli "Federico II", Dipartimento delle Scienze Biologiche, Via Foria 223, 80139 Napoli, Italy

author email corresponding author email

BMC Evolutionary Biology 2008, 8:27doi:10.1186/1471-2148-8-27

Published:	28 January 2008

Abstract

Background

Within the astonishing diversity of orchid pollination systems, sexual deception is one of the most stunning. An example is the genus Ophrys, where plants attract male bees as pollinators by mimicking female mating signals. Unsaturated hydrocarbons (alkenes) are often the key signal for this chemical mimicry. Here we investigate the evolution of these key compounds within Orchidinae by mapping their production in flowers of selected species onto their estimated phylogeny.

Results

We found that alkenes, at least in trace amounts, were present in 18 of 20 investigated species together representing 10 genera. Thus, the reconstruction of ancestral state for alkene-production showed that this is a primitive character state in Ophrys, and can be interpreted as a preadaptation for the evolution of sexual deception. Four of the investigated species, namely Ophrys sphegodes, Serapias lingua, S. cordigera, and Anacamptis papilionacea, that are pollinated primarily by male bees, produced significantly larger amounts and a greater number of different alkenes than the species pollinated either primarily by female bees or other insects.

Conclusion

We suggest that high amounts of alkenes evolved for the attraction of primarily male bees as pollinators by sensory exploitation, and discuss possible driving forces for the evolution of pollination by male bees.

[Article]Conflict btw natural & sexual selection due to mmicry

Interspecific sexual attraction because of convergence in warning colouration: is there a conflict between natural and sexual selection in mimetic species?

Journal of Evolutionary Biology

Volume 21 Issue 3 Page 749-760, May 2008

Citation: C. ESTRADA, C. D. JIGGINS (2008) Interspecific sexual attraction because of convergence in warning colouration: is there a conflict between natural and sexual selection in mimetic species? Journal of Evolutionary Biology 21 (3) , 749–760 doi:10.1111/j.1420-9101.2008.01517.x

Abstract

When species converge in their colour patterns because of mimicry, and those patterns are also used in mate recognition, there is a probability of conflicting selection pressures. Closely related species that mimic one another are particularly likely to face such confusion because of similarities in their courtship behaviour and ecology. We conducted experiments in greenhouse conditions to study interspecific attraction between two mimetic butterfly species, Heliconius erato and Heliconius melpomene. Both species spent considerable time approaching and courting females of the co-mimic species. Experiments using wing models demonstrated the importance of colour pattern in this interspecific attraction. Although males of H. melpomene were attracted to their co-mimics as much as to their own females, H. erato males were more efficient at distinguishing conspecifics, possibly using wing odours. Although preliminary, these results suggest that the use of additional cues may have evolved in H. erato to reduce the cost of convergence in visual signals with H. melpomene. Overall, our results showed that there might be a cost of mimetic convergence because of a reduction in the efficiency of species recognition. Such cost may contribute to explain the apparently stable diversity in Müllerian mimetic patterns in many tropical butterfly assemblages.

[Article: Predation]Predators Make (Temporary) Escape from Coevolutionary Arms Race

Predators Make (Temporary) Escape from Coevolutionary Arms Race

Liza Gross

Citation: Gross L (2008) Predators Make (Temporary) Escape from Coevolutionary Arms Race. PLoS Biol 6(3): e75 doi:10.1371/journal.pbio.0060075

Published: March 11, 2008

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Arguably cute and spanning at most 20 cm from head to tail, the rough-skinned newt packs pretty near the most poisonous punch known to the animal kingdom. Taricha granulosa, like all species in its genus, exudes an exceptionally potent neurotoxin, tetrodotoxin (TTX) from its skin glands. Some Taricha newts could wipe out thousands of mice or a clutch of humans with their toxic issue. But why produce enough poison to kill a potential predator several times over? To discourage the one predator—the common garter snake (Thamnophis sirtalis)—that's resistant enough to the poison to count on newts as a food source.

URL: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0060075

Phenotypic Mismatches Reveal Escape from Arms-Race Coevolution

Charles T. Hanifin^1¤*, Edmund D. Brodie Jr.¹, Edmund D. Brodie III²

1 Department of Biology, Utah State University, Logan, Utah, United States of America, 2 Department of Biology, University of Virginia, Charlottesville, Virginia, United States of America

Because coevolution takes place across a broad scale of time and space, it is virtually impossible to understand its dynamics and trajectories by studying a single pair of interacting populations at one time. Comparing populations across a range of an interaction, especially for long-lived species, can provide insight into these features of coevolution by sampling across a diverse set of conditions and histories. We used measures of prey traits (tetrodotoxin toxicity in newts) and predator traits (tetrodotoxin resistance of snakes) to assess the degree of phenotypic mismatch across the range of their coevolutionary interaction. Geographic patterns of phenotypic exaggeration were similar in prey and predators, with most phenotypically elevated localities occurring along the central Oregon coast and central California. Contrary to expectations, however, these areas of elevated traits did not coincide with the most intense coevolutionary selection. Measures of functional trait mismatch revealed that over one-third of sampled localities were so mismatched that reciprocal selection could not occur given current trait distributions. Estimates of current locality-specific interaction selection gradients confirmed this interpretation. In every case of mismatch, predators were “ahead” of prey in the arms race; the converse escape of prey was never observed. The emergent pattern suggests a dynamic in which interacting species experience reciprocal selection that drives arms-race escalation of both prey and predator phenotypes at a subset of localities across the interaction. This coadaptation proceeds until the evolution of extreme phenotypes by predators, through genes of large effect, allows snakes to, at least temporarily, escape the arms race.

URL: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0060060

[Team]Jim Mallet (University College London)

Research themes

Primarily directed towards answering a basic, but still poorly understood riddle: how do new species arise? His group focuses on evolution and ecology of butterflies and moths (Lepidoptera), particularly near the species boundary. The Lepidoptera form 15-20% of the world's described species, yet are poorly known genetically.

(1) Hybridization and evolution in Heliconius butterflies
(2) Taxonomy, mimicry and biogeography in the Ithomiinae

Although his primary interests are in genetic and systematic studies of populations, geographic forms, and speciation, many of his results have obvious implications for conservation of endangered taxa. He remains committed to and interested in topics such as insecticide resistance, safety concerns about the release of genetically modified organisms (GMOs), and in the biodiversity and conservation applications of his work.

URL: http://www.ucl.ac.uk/taxome/jim/

[Article]Juvenile Hormone Regulates Butterfly Larval Pattern Switches

Abstract:

Juvenile Hormone Regulates Butterfly Larval PatternSwitches

Ryo Futahashi^1,2 and Haruhiko Fujiwara^1*

Insect color patterns can be very diverse. This variation is also seen among many larval instar stages, which can take on vastly different phenotypes. Young caterpillars of the swallowtail butterfly, Papilio xuthus, are mimics of bird droppings, whereas the fifth larval instar is camouflaged among the leaves of host plants (cryptic pattern). We find that juvenile hormone (JH) titers decrease during the fourth larval instar. Furthermore, treatment with JH analog at the beginning of the fourth instar stage resulted in reproducing the mimetic pattern instead of the usual cryptic one and likewise altered gene expression patterns to that associated with the mimetic pattern. These findings suggest that JH regulates the progressive larval pattern switch of this insect.

¹ Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience Building 501, Kashiwa, Chiba 277-8562, Japan.
² National Institute of Agrobiological Sciences, 1-2 Owashi, Tsukuba, Ibaraki 305-8634, Japan.

^* To whom correspondence should be addressed. E-mail: haruh@k.u-tokyo.ac.jp
URL: http://www.sciencemag.org/cgi/content/full/319/5866/1061?rss=1

[Video]Butterfly wings under UV

http://youtube.com/watch?v=7rkWeyUURts

[Video]Animal camouflage & mimicry on youtube

http://youtube.com/watch?v=zC0zOLqYnRg
http://youtube.com/watch?v=7ujRgSRYE9A
http://youtube.com/watch?v=SCgtYWUybIE&feature=related

(第三段影片是焦傳金老師演講時使用過的video clip)

[Article]Can experienced birds select for Müllerian mimicry?

link: http://tinyurl.com/2m6zlz
Ihalainen, E. et al. 2008. Behav. Ecol. 19: 362-368
Abstract: Field experiments have shown that avian predators in the wild can select for similarity of warning signals in aposematic prey (Müllerian mimicry) because a common signal is better protected than a signal that is novel and rare. The original theory of Müllerian mimicry assumes that the mechanism promoting mimicry is predator learning; by sharing a signal, the comimic species share the mortality that is due to sampling by inexperienced predators. Predation events have not been observed in the wild, and learning experiments with naive bird predators in a laboratory have not unambiguously shown a benefit of a uniform signal compared with different signals. As predators in the field experiments are likely to be more experienced compared with previous laboratory experiments, we studied selection by experienced predators on a novel imperfect mimic. We trained great tits Parus major to avoid artificial aposematic models and subsequently introduced perfect and imperfect mimics at different frequencies. Birds with prior experience on the models selected against the imperfect mimics that were at a disadvantage also in a memory test conducted a week after their introduction. Selection against the imperfect mimics was antiapostatic. However, the imperfect mimics also benefited from some signal generalization to the models and possibly gained protection because the birds were familiar with the alternative cryptic prey that was also present. Our results suggest that experienced predators might be more important to the evolution of mimicry than the learning-based theory assumes.

[Article]A Conserved Supergene Locus Controls Colour Pattern Diversity in Heliconius Butterflies

Link: http://0rz.tw/733NG
Abstract: We studied whether similar developmental genetic mechanisms are involved in both convergent and divergent evolution. Mimetic insects are known for their diversity of patterns as well as their remarkable evolutionary convergence, and they have played an important role in controversies over the respective roles of selection and constraints in adaptive evolution. Here we contrast three butterfly species, all classic examples of Müllerian mimicry. We used a genetic linkage map to show that a locus, Yb, which controls the presence of a yellow band in geographic races of Heliconius melpomene, maps precisely to the same location as the locus Cr, which has very similar phenotypic effects in its co-mimic H. erato. Furthermore, the same genomic location acts as a “supergene”, determining multiple sympatric morphs in a third species, H. numata. H. numata is a species with a very different phenotypic appearance, whose many forms mimic different unrelated ithomiine butterflies in the genus Melinaea. Other unlinked colour pattern loci map to a homologous linkage group in the co-mimics H. melpomene and H. erato, but they are not involved in mimetic polymorphism in H. numata. Hence, a single region from the multilocus colour pattern architecture of H. melpomene and H. erato appears to have gained control of the entire wing-pattern variability in H. numata, presumably as a result of selection for mimetic “supergene” polymorphism without intermediates. Although we cannot at this stage confirm the homology of the loci segregating in the three species, our results imply that a conserved yet relatively unconstrained mechanism underlying pattern switching can affect mimicry in radically different ways. We also show that adaptive evolution, both convergent and diversifying, can occur by the repeated involvement of the same genomic regions.

[Article]Cognitive Dimensions of Predator Responses to Imperfect Mimicry

Link: http://0rz.tw/633Np
Abstract: Many palatable animals, for example hoverflies, deter predators by mimicking well-defended insects such as wasps. However, for human observers, these flies often seem to be little better than caricatures of wasps—their visual appearance and behaviour are easily distinguishable from those which they are attempting to mimic. This imperfect mimicry baffles evolutionary biologists, because one might expect natural selection to do a more thorough job. Here we discuss two types of cognitive processes that might explain why distinguishable mimics could enjoy increased protection from predation. Speed–accuracy tradeoffs in predator decision making might give imperfect mimics sufficient time to escape, and predators under time constraint might avoid time-consuming discriminations between well-defended models and inaccurate edible mimics and instead adopt a “safety first” policy of avoiding insects with similar appearance. Categorisation of prey types by predators could mean that wholly dissimilar mimics may be protected, provided they share some common property with noxious prey. If predators use experience with multiple prey types to learn rules rather than just memorising the appearance of individual prey types, it follows that different individual predators should form different categories, each including separate types of novel prey. Experimental studies to test these hypotheses should be straightforward, because we can use the relatively simple signals (e.g., striped patterns) with which prey manipulate predator behaviour as tools for investigating cognitive processes that underlie decision making and object recognition in animals' daily lives.