眼紋的禦敵功能到底是什麼?

Vallin A, Dimitrova M, Kodandaramaiah U, Merilaita S. (2011) Deflective effect and the effect of prey detectability on anti-predator function of eyespots. Behav Ecol Sociobiol. 65:1629–1636. DOI 10.1007/s00265-011-1173-7[full text]

同心圓的眼紋一般被學者認為是具有禦敵的功能，並於早期實驗得知其具有威嚇天敵的作用，但近期研究發現，眼紋威嚇天敵的作用並非來自於形狀與眼睛相似，而是對比、顯眼性等因素，但眼紋於自然界中仍為十分常見的存在方式，因此作者試圖了解眼紋存在的理由。作者以藍山雀(Cyanistes caeruleus)作為捕食者，以三角型的紙片製成人工獵物(b × h: 30×15 mm2)，再控制獵物的眼紋的大小、數量(0、1、2)和背景差異(以27×21 cm紙板改變獵物背景色)，總共分成兩個實驗，去看不同獵物對捕食者反應的影響。結果顯示：(a) 小眼紋比大眼紋易受到攻擊 (b)獵物和背景的突出程度會比眼紋大小更具影響力 (c) 捕食者的迴避行為在成對眼紋時會比無眼紋好 (d) 威嚇作用只出現在隱避性背景的部分 (e) 眼紋大小和單一大眼紋及無眼紋間無顯著差異。所以總結實驗結果，作者認為影響眼紋功能的主要因子是眼紋和背景的差異度，但天敵的攻擊行為會偏好小型眼紋，表示對天敵為小型的雀形目物種的獵物而言，天敵會攻擊眼紋而避免攻擊獵物本身的重要部位。

偽裝有利於存活的先決條件是什麼?

[image Selenia dentaria][image Prunus spinosa]
Skelhorn J, Ruxton GD. (2011) Context-dependent misclassification of masquerading prey. Evol Ecol. 25:751–761. DOI 10.1007/s10682-010-9435-9

部份的物種會以改變自己的外觀或行為等方式達到隱蔽的作用，而這些方式稱為偽裝，並且相較於正常獵物，無經驗的捕食者較不容易發現偽裝的獵物。在此，作者以小雞作為捕食者，以Selenia dentaria作為偽裝的獵物，其幼蟲被認為有偽裝寄主植物(Prunus spinosa)的能力，再 (1)改變樹枝背景使獵物顯眼性產生差異 (2)改變獵物和枝條的量，結果顯示，當獵物數較多且和背景相比較突出時，對有經驗的捕食者而言是最有利的；在與背景相比，顯眼性差的獵物其捕食者攻擊延遲的時間也比較久。因此，作者認為結果顯示偽裝可能要付出代價，且捕食者的決定可能是相當複雜而受多因子影響的。

警戒性與貝氏擬態是否一定需要醒目顏色配合? 研究顯示歐洲蝮蛇的隱匿但具辯識性的斑紋可避免掠食者的攻擊

文獻來源: WüSTER W, ALLUM CSE, BIRTA BJARGARDOTTIR I, BAILEY KL, DAWSON KJ, GUENIOUI J, LEWIS J, MCGURK J, MOORE AG, NISKANEN M, POLLARD CP. 2004. Do aposematism and Batesian mimicry require bright colours? A test, using European viper markings. Proceedings of the Royal Society of London. Biological sciences 271(1556): 2495-2499. [全文下載]

Abstract
Predator avoidance of noxious prey, aposematism and defensive mimicry are normally associated with bright, contrasting patterns and colours. However, noxious prey may be unable to evolve conspicuous coloration because of other selective constraints, such as the need to be inconspicuous to their own prey or to specialist predators. Many venomous snakes, particularly most vipers, display patterns that are apparently cryptic, but nevertheless highly characteristic, and appear to be mimicked by other, non-venomous snakes. However, predator avoidance of viper patterns has never been demonstrated experimentally. Here, the analysis of 813 avian attacks on 12 636 Plasticine snake models in the field shows that models bearing the characteristic zigzag band of the adder (Vipera berus) are attacked significantly less frequently than plain models. This suggests that predator avoidance of inconspicuously but characteristically patterned noxious prey is possible. Our findings emphasize the importance of mimicry in the ecological and morphological diversification of advanced snakes.

圖片連結: wikipedia (photo credit: Marek Szczepanek)

透明小魚蝦的群聚可能是一種閃避視覺系捕食者的防禦策略, 並牽涉數量擬態(或稱社會擬態)

文獻來源: Carvalho LN, Zuanon J, Sazima I. 2009. The almost invisible league: crypsis and association between minute fishes and shrimps as a possible defence against visually hunting predators. Neotropical Ichthyology 4(2): doi: 10.1590/S1679-62252006000200008

Abstract
Camouflage is one of the most widespread defence modes used by substrate-dwelling animals, whereas transparency is generally found in open-water organisms. Both these defence types are regarded as effective against visually guided predators. We present here three assemblages of similarly-sized freshwater fish and shrimp species which apparently rely on camouflage and transparency to evade some of their potential predators. In one of the associations, there is a transition from cryptic colours and translucency to transparency of the component species according to the position each of them occupies in the habitat. The likeness between the fishes and the shrimps is here regarded as a type of protective association similar to numerical or social mimicry. Additionally, we suggest that the assemblage may contain Batesian-like mimicry components.

圖片連結: Aquaristik ohne Geheimnisse

[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: 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.

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