為何車前燈蛾的翅紋多樣性可以長期存在？

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Nokelainen O, Hegna RH, Reudler JH, Lindstedt C, Mappes J. 2011. Trade-off between warning signal efficacy and mating success in the wood tiger moth. Proc. R. Soc. B. doi: 10.1098/rspb.2011.0880 [full text]

從演化的觀點來看，特徵選汰應傾向於對物種存活有利的方式，並且，後期這些基因特質應達到穩定且妨礙多態型的存在，但有許多警戒色的例子顯示多態型的物種是可以同時存在於相同族群中，其顯示不同型態之特徵可能具有不同優勢存在，或其可能具有相同功效。在此，作者以具有明顯翅紋變異的白色及黃色車前燈蛾(Parasemia plantaginis)作為獵物，以藍山雀(Parus caeruleus)作為捕食者測試翅紋警戒色在存活率和繁殖成功率之間的關係。結果顯示：(a)捕食者對於黃色翅紋有較長的攻擊延遲時間 (b)黃色翅紋的個體存活率比白色翅紋的個體好 (c)白色翅紋的個體繁殖成功率比黃色翅紋個體好，因此，作者認為此結果正好為車前燈蛾白色及黃色翅紋同時共存於自然界作一個很好的解釋。

掠食者的保守食性使得稀少且醒目的獵物得以生存

Marples NM, Mappes J. (2011) Can the dietary conservatism of predators compensate for positive frequency dependent selection against rare, conspicuous prey? Evol Ecol. 25:737–749. DOI: 10.1007/s10682-010-9434-x

簡介
由於顯眼性色彩容易吸引天敵的注意，警戒色在演化初期對獵物來說是不利且少見的，但若長期只供給相同獵物時，此獵物顯眼性表型中的anti-apostatic個體將被選汰出來。因此，作者以大山雀作為捕食者，杏仁作為人工獵物，測試於隱蔽獵物中19代顯眼性個體和捕食者的捕食行為之關係。結果發現，顯眼性獵物在初級的被攻擊率最高，使具警戒功能的顯眼性個體無法存活，但期捕食者有17隻(24%)會拒決捕食顯眼性獵物。因此，顯眼性獵物要在隱蔽族群中存活是困難的，但在捕食者的捕食行為篩選下，會促使警戒色在演化中被保存。

環境背景和掠食者的覓食行為有什麼關係？

[圖片來源: http://online-field-guide.com/Chaunusmarinus.htm]

González-Bernal E, Brown GP, Cabrera-Guzmán E & Shine R. (2011) Foraging tactics of an ambush predator: the effects of substrate attributes on prey availability and predator feeding success. Behav. Ecol. Sociobiol. 65: 1367-1375. DOI: 10.1007/s00265-011-1147-9

掠食者在覓食時會挑選適合埋伏的地點，例如甘蔗蟾蜍(Rhinella marina)會選擇在有人工光源的開擴地覓食。作者將實驗分成兩部份：首先，野外實驗將橡膠墊(1.5×1.5 m)置於野外光源下的地面進行實驗，看在不改變墊子數量、大小及獵物種類之下，不同色彩(黑色和白色)及紋路(光滑和粗糙)之間對捕食行為的影響，結果發現蟾蜍偏好白色粗糙的墊子；另外，作者也進行室內實驗去控制獵物的色彩，發現 (1)白色背景下，捕食者便於搜尋深色獵物 (2)粗糙背景時，獵物的移動速度也會降低。因此，動物的覓食行為，不單只受獵物密度影響，也會受覓食環境的影響。

鳥類能夠學習用不適口度做為獵物有毒程度的訊號

photo from http://www.tamstuart.com/

Source: Skelhorn J. & Rowe C. (2010) Birds learn to use distastefulness as a signal of toxicity. Proc. R. Soc. B. (in press) [abstract]

具有警戒色的獵物展示顯眼的體色用以警告它們的捕食者其不適口度，並且讓捕食者迅速的學習避免再度攻擊同類的獵物。雖然這樣的機制能夠有效的讓捕食者學習避免捕食，但卻沒有讓捕食者知道到底獵物有多不好吃，而這牽扯到如何能將不適口度較低的獵物包含在捕食者的飲食內，並在這樣的獵物中取得最大能量與生理上抵抗其毒性間取得平衡。因此，捕食者應該要能夠判斷這些受保護的獵物中的毒性高低。在本篇文章的實驗中，作者使用歐洲椋鳥(European starling)做為捕食者，並且測得其能夠利用苦味的程度預測該個體體內含毒的程度，並且使用這樣的資訊進一步選擇毒性較低的獵物，以增加自身取得能量的最大值。本篇的結果支持苦味是一種能夠反應毒性的訊號，並且能夠解釋為何大多數的毒物皆具有苦味。而這個結果也提供了未來若要使用函數模擬獵物的防禦的演化時，應考慮捕食者根據毒性與取得的營養間的平衡所做的決定。

[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: 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