Fig. 1 織布鳥與寡婦鳥的親緣關係。圖中框起來的就是本文主角－雌性寄生織布鳥。在其上的是擬態的模型，紅寡婦鳥（雄性紅色那隻）。

標題：Evidence for aggressive mimicry in an adult brood parasitic bird, and generalized defences in its host.

美洲知更鳥 (Turdus migratorius) photo: American robin (wiki)

標題：Experimental Shifts in Intraclutch Egg Color Variation Do Not Affect Egg Rejection in a Host of a Non-Egg-Mimetic Avian Brood Parasite

摘要

褐頭牛鸝 (Molothrus ater) photo: Brown-headed cowbird (wiki)

褐頭牛鸝與美洲知更鳥的蛋 photo: Don Johnston

Fig. 1 實驗進行所使用的鳥蛋顏色與反射光譜數據

Fig. 2 增加或減少鳥蛋顏色的條件下，知更鳥排除的比例

Radix balthica photo: Mollusca of Belarus

標題：Camouflaged or tanned: plasticity in freshwater snail pigmentation.

摘要

By having phenotypically plastic traits, many organisms optimize their fitness in response to fluctuating threats. Freshwater snails with translucent shells, e.g. snails from the Radix genus, differ considerably in their mantle pigmentation patterns, with snails from the same water body ranging from being completely dark pigmented to having only a few dark patterns. These pigmentation differences have previously been suggested to be genetically fixed, but we propose that this polymorphism is owing to phenotypic plasticity in response to a fluctuating environment. Hence, we here aimed to assess whether common stressors, including ultraviolet radiation (UVR) and predation, induce a plastic response in mantle pigmentation patterns of Radix balthica.We show, in contrast to previous studies, that snails are plastic in their expression of mantle pigmentation in response to changes in UVR and predator threats, i.e. differences among populations are not genetically fixed. When exposed to cues from visually hunting fish, R. balthica increased the pro- portion of their dark pigmentation, suggesting a crypsis strategy. Snails increased their pigmentation even further in response to UVR, but this also led to a reduction in pattern complexity. Furthermore, when exposed to UVR and fish simultaneously, snails responded in the same way as in the UVR treatment, suggesting a trade-off between photoprotection and crypsis.

對於一個生物個體來說，牠能呈現出的體色來自很多不同方面的限制，遺傳框限多樣性，性擇決定這性狀是否受青睞，天擇直接讓不適合的個體從世界上說再見，還要考慮是不是能適應環境。面對這複雜的世界，不同區域的族群，甚至個體，受到的壓力可能不同，因此生物的顏色出現差異，造就物種體色多態性(polymorphism) 的生成。這又觸動科學家們那條求知旺盛的神經：究竟這些生物是受到什麼因素，讓不同顏色個體的適存度有差異？

蘿蔔螺屬（Radix，椎實螺科 Lymnaeidae）是個淡水螺，其螺殼基本上是褐色，帶有黑色的斑紋，有些種類不同族群的黑色斑紋比例會有差異，之前的研究認為這個差異來自遺傳限制，就是因為A族群黑的少生下來也黑的少，B族群黑的多生下來也黑的多。但本篇的作者群似乎不這麼認為。面對波動的環境，遺傳的限制可能只是淘汰的結果而不是原因，因此作者群透過本篇的主角R. balthica，來討論這樣的顏色差異是為了隱蔽起來躲避天敵，或是為了抵抗不利環境因子。

Fig. 1 螺殼在不同因子下的變化

實驗中使用的捕食者黑鯽魚 (Carassius carassius) photo: 黑鯽 (wiki)

作者群從瑞典南方的隆德(Lund)附近的池塘中，蒐集大約300個個體到實驗室繁殖。實驗主要討論兩個因素：捕食者與紫外線(UV)是否讓個體的黑色素形成，因此將螺分成四組：控制組（無壓力）、捕食者組（以飼養的黑鯽魚 Carassius carassius 的化學訊號溶於水中）、UV組（以螢光燈照射）、捕食者+UV組，實驗進行八週，結束後再把這些螺拿來拍照，分析黑色斑紋的比例。

Fig. 2 上圖說明黑色區域的比例，下圖為色素覆蓋的複雜度

結果顯示黑色斑紋的佔殼的面積依控制組、捕食者、UV、捕食者+UV，顯著的變大，而斑紋的複雜度在面對捕食者時最高，捕食者+UV時最低。分析中捕食者與UV兩因素皆無統計上的交互作用。這代表R. balthica的斑紋變異並非來自遺傳，而是來自不同的環境因子。當面對視覺捕食者時，讓斑紋變的複雜，表示採取隱蔽的策略，而在UV照射的環境下則增加黑色斑紋的覆蓋抗UV，但這讓斑紋的複雜度下降。若同時暴露在兩個因子下，斑紋的變化比較接近只有UV的變化，顯示在這兩個因子間，UV照射的風險比起被捕食的風險還高，也支持這是顏色選擇上的權衡(trade off)。

小丑箭毒蛙 (Oophaga granulifera)紅色型 photo: ARKive

標題：NOT EVERYTHING IS BLACK AND WHITE: COLOR AND BEHAVIORAL VARIATION REVEAL A CONTINUUM BETWEEN CRYPTIC AND APOSEMATIC STRATEGIES IN A POLYMORPHIC POISON FROG

摘要

Aposematism and crypsis are often viewed as two extremes of a continuum of visual conspicuousness to predators. Theory predicts that behavioral and coloration conspicuousness should vary in tandem along the conspicuousness spectrum for antipredator strategies to be effective. Here we used visual modeling of contrast and behavioral observations to examine the conspicuousness of four populations of the granular poison frog, Oophaga granulifera, which exhibits almost continuous variation in dorsal color. The patterns of geographic variation in color, visual contrast, and behavior support a gradient of overall conspicuousness along the distribution of O. granulifera. Red and green populations, at the extremes of the color distribution, differ in all elements of color, contrast, and behavior, strongly reflecting aposematic and cryptic strategies. However, there is no smooth cline in any elements of behavior or coloration between the two extremes. Instead populations of intermediate colors attain intermediate conspicuousness by displaying different combinations of aposematic and cryptic traits. We argue that coloration divergence among populations may be linked to the evolution of a gradient of strategies to balance the costs of detection by predators and the benefits of learned aversion.

photo from Bgreenproject

標題：An Analysis of Predator Selection to Affect Aposematic Coloration in a Poison Frog Species

摘要

Natural selection is widely noted to drive divergence of phenotypic traits. Predation pressure can facilitate morphological divergence, for example the evolution of both cryptic and conspicuous coloration in animals. In this context Dendrobatid frogs have been used to study evolutionary forces inducing diversity in protective coloration. The polytypic straw- berry poison frog (Oophaga pumilio) shows strong divergence in aposematic coloration among populations. To investigate whether predation pressure is important for color divergence among populations of O. pumilio we selected four mainland populations and two island populations from Costa Rica and Panama. Spectrometric measurements of body coloration were used to calculate color and brightness contrasts of frogs as an indicator of conspicuousness for the visual systems of several potential predators (avian, crab and snake) and a conspecific observer. Additionally, we conducted experiments using clay model frogs of different coloration to investigate whether the local coloration of frogs is better protected than non-local color morphs, and if predator communities vary among populations. Overall predation risk differed strongly among populations and interestingly was higher on the two island populations. Imprints on clay models indicated that birds are the main predators while attacks of other predators were rare. Furthermore, clay models of local coloration were equally likely to be attacked as those of non-local coloration. Overall conspicuousness (and brightness contrast) of local frogs was positively correlated with attack rates by birds across populations. Together with results from earlier studies we conclude that conspicuousness honestly indicates toxicity to avian predators. The different coloration patterns among populations of strawberry poison frogs in combination with behavior and toxicity might integrate into equally efficient anti-predator strategies depending on local predation and other ecological factors.

草莓箭毒蛙(Oophaga pumilio)是個不同族群長的不一樣的多態性物種，而且每個族群呈現不同的警戒性。這樣的現象通常引起科學家的興趣，因為這可能代表背後不同的選汰力量，也牽涉到潛在的種化趨勢，這些難解的問題到底來自天擇，還是來自性擇，還是來自其他未知的力量？

不同族群在不同視覺模型下的相對亮度與相對顏色 photo from Fig. 1

這篇文章的作者想測試草莓箭毒蛙的多態性是不是來自天擇（捕食者）的選擇，他們選擇在哥斯大黎加與巴拿馬附近，四個大陸上的與兩個島嶼上族群來調查。測試分成兩個部分，一個部分是分別測量不同族群個體背面與腹面的反射光譜，然後套用鳥類、螃蟹與蛇的視覺模型，判斷哪些可能是潛在捕食者；另一個部分作者製作四個顏色的黏土模型（紅、黃、綠、藍），然後分別放了400隻模型，分了四次放到自然環境中，每個族群總共放1600隻黏土模型測試被攻擊次數。如果有攻擊的話，可以分為鳥（U或V型）、老鼠、蛇、蜥蜴、與未知的捕食標記。

不同族群的被攻擊數，灰色來自鳥類，黑色來自其他攻擊 photo from Fig. 2

綜合6個族群，不同顏色的被攻擊數 photo from Fig. 3

反射光譜的部分各有千秋，細節詳見內文。整體來說背部紅/橘與黃色的族群的顯眼度整體高於藍色與綠色，腹部的顯眼度基本上沒有差異，但Isla Colon的腹部黃色比起Isla Solarte的顯眼度差不多或稍高。捕食實驗的結果每個族群各有差異，兩個島嶼族群的被攻擊數比較高，然而如同當地顏色的黏土模型的被攻擊數與非當地顏色的沒有差異。整體來說大部分的攻擊都來自鳥類，來自其他的攻擊顯著的比起鳥類少很多。綜合這個研究與之前的研究，不同顏色的不同族群忠實的反應其毒性。儘管毒性有所不同，但配合不同的行為調整，可能可以讓不同族群的防禦效益，讓族群間的「防禦值」達到同樣的水準，反應不同的捕食壓力與其他的生態因子。

這個文章整體看起來，捕食者對多態型的形成主要的壓力是來自鳥類，然而細緻的型態演化本篇沒有多著墨，大概還是跟不同種的鳥類認知與細膩的演化有關。總和近期的文章來看，捕食者到底認得什麼似乎是個重要的關鍵，或許這些作者可以考慮使用3D列印，真正印出類似的斑紋，替代單純的只使用顏色分類的模型，可能可以比較反應真實的情況。

標題：PREDATOR PERCEPTION OF BATESIAN MIMICRY AND CONSPICUOUSNESS IN A SALAMANDER

摘要

In Batesian mimicry a palatable mimic deceives predators by resembling an unpalatable model. The evolution of Batesian mimicry relies on the visual capabilities of the potential predators, as prey detection provides the selective force driving evolutionary change. We compared the visual capabilities of several potential predators to test predictions stemming from the hypothesis of Batesian mimicry between two salamanders: the model species Notophthalmus viridescens, and polymorphic mimic, Plethodon cinereus. First, we found mimicry to be restricted to coloration, but not brightness. Second, only bird predators appeared able to discriminate between the colors of models and nonmimic P. cinereus. Third, estimates of salamander conspicuousness were background dependent, corresponding to predictions only for backgrounds against which salamanders are most active. These results support the hypothesis that birds influence the evolution of Batesian mimicry in P. cinereus, as they are the only group examined capable of differentiating N. viridescens and nonmimetic P. cinereus. Additionally, patterns of conspicuousness suggest that selection from predators may drive the evolution of conspicuousness in this system. This study confirms the expectation that the visual abilities of predators may influence the evolution of Batesian mimicry, but the role of conspicuousness may be more complex than previously thought.

對擬態/警戒性的物種來說，重要的是這些顏色相對於背景來說夠不夠明顯，捕食者能不能看見，進而產生知覺的連結，費心經過天擇篩選出來的體色才能在自然界中綻放其光彩。

這個研究就在測試這個簡單的概念，對象是分佈於北美洲的火焰蠑螈 (Notophthalmus viridescens)與紅背蠑螈 (Plethodon cinereus)這個貝氏擬態群，藉由測量背部單點的反射光譜，與泥土、濕葉子、乾葉子的反射光譜相比，並且套用東方襪帶蛇 (Thamnophis sirtalis)、十三線地松鼠 (Spermophilus tridecemlineatus)與藍山雀 (Cyanistes caeruleus)分別代表三種不同的捕食者的視覺模型，統計有哪些捕食者可以看的到。結果顯示這個擬態的現象侷限於顏色(color)，而不是亮度(brightness)；視覺模型的統計中，只有鳥類能分辨火焰蠑螈與非擬態的紅背蠑螈；與背景比較的話，這些蠑螈與預期的一樣十分明顯。

不過如果仔細看內文的統計數據會發現一些有趣的事情，作者用三種不同的背景比較顯眼度，雖然著墨不多，但其實蛇與哺乳類對於不同背景的亮度還是有統計上的差異，若只從視覺模型這點來看，我想這些捕食者還是看的到某些東西，而我們對於蛇類與除了白鼠外的小型哺乳類的認知幾乎一無所知，即使只能透過亮度的差異，是不是就能達到警戒性的功用也未可知，作者把結論導向這個選汰的主力是鳥類捕食者，也只是因為在顏色的辨別達到統計上的顯著差異，未來透過同類型的捕食者的行為實驗或許能帶來更多結果。

不過有意思的是，作者在之後的研究（看這裡）裡說兩種蠑螈的亮度是隨族群有差異的，如果這個擬態群只有顏色影響其作用的話，那麼亮度為何需要變動？（或許是為了其他理由，如求偶）反過來說，亮度的變動有沒有可能反而是為了那些看不到顏色的捕食者，讓牠們能「看見」（警戒）或「看不見」（隱蔽）？

Conspicuousness, or having high contrast relative to the surrounding back- ground, is a common feature of unpalatable species. Several hypotheses have been proposed to explain the occurrence of conspicuousness, and while most involve the role of conspicuousness as a direct signal of unpalat- ability to potential predators, one hypothesis suggests that exaggerated conspicuousness may evolve in unpalatable species to reduce predator confusion with palatable species (potential Batesian mimics). This hypothesis of antagonistic coevolution between palatable and unpalatable species hinges on the ‘cost of conspicuousness’, in which conspicuousness increases the likelihood of predation more in palatable species than in unpalatable species. Under this mimicry scenario, four patterns are expected: (i) mimics will more closely resemble local models than models from other localities, (ii) there will be a positive relationship between mimic and model conspicuousness, (iii) models will be more conspicuous in the presence of mimics, and (iv) when models and mimics differ in conspicuousness, mimics will be less conspicuous than models. We tested these predictions in the salamander mimicry system involving Notophthalmus viridescens (model) and one colour morph of Plethodon cinereus (mimic). All predictions were supported, indicating that selection for Batesian mimicry not only influences the evolution of mimics, but also the evolution of the models they resemble. These findings indicate that mimicry plays a large role in the evolution of model warning signals, particularly influencing the evolution of conspicuousness.

標題：Mimicry refinement: Phenotypic variations tracking the local optimum [pdf]

摘要

1.Müllerian mimicry between chemically defended preys is a textbook example of natural selection favouring phenotypic convergence onto a shared warning signal. Studies of mimicry have concentrated on deciphering the ecological and genetic underpinnings of dramatic switches in mimicry association, producing a well-known mosaic distribution of mimicry patterns across geography. However, little is known about the accuracy of resemblance between natural co-mimics when the local phenotypic optimum varies.

2.In this study, using analyses of wing shape, pattern and hue, we quantify multimodal phenotypic similarity between butterfly co-mimics sharing the so-called postman pattern in different localities with varying species composition.

3.We show that subtle but consistent variation between populations of the localised species, Heliconius timareta thelxinoe, enhance resemblance to the abundant co-mimics which drive the mimicry in each locality.

4.Those results suggest that rarer co-mimics track the changes in the phenotypic optimum caused by gradual changes in the composition of the mimicry community, providing insights into the process by which intra-specific diversity of mimetic pattern may arise. Furthermore, our results suggest a multimodal evolution of similarity, with coordinated convergence in different features of the phenotype such as wing outline, pattern and hue.

5.Finally, multilocus genotyping allows estimating local hybridization rates between H. timareta and co-mimic H. melpomene in different populations, raising the hypothesis that mimicry refinement between closely-related co-mimics may be enhanced by adaptive introgression at loci modifying the accuracy of resemblance.
無論從哪個角度來說，穆氏擬態群內的斑紋應該要越相似越好，如果有個體長的突然與大家不一樣，可能就會被天擇排擠消失，也或許有機會獨樹一格（低機率），雖然人類視覺角度來看，穆氏擬態群的每個物種或個體都十分相似，但之前已經有研究指出不同種間的相似斑紋來源可能是透過不同的基因調控來的，若是如此，自然界中展現出來的表型看起來雖然一致，但會不會是在某個可接受的誤差範圍內呢？

這篇研究討論毒蝶的一個稱做「郵差」(postman)的擬態型，參與這個擬態型的物種有H. melpomene, H. timareta, H. erato, H. timareta, H. telesiphe，之所以會有這樣的考量在於其中有個共擬態亞種H. timareta thelxinoe在兩個區域的族群有些微的變化，而這兩地的model也剛好有這樣的不同。作者測量這些蝴蝶的翅型、翅紋樣式與色調來比較這兩個族群間的差異是否一致。結果顯示H. timareta thelxinoe的斑紋在兩地間有連續性的變化，支持穆氏擬態中斑紋應該與當地的model趨近的觀點。

這也是個model強烈的主導mimic的斑紋變化，在天擇的作用下，mimic透過細微的改變趨近model的一證據。（自然界中的霸凌？）

標題：A bird's eye view of two mimetic tropical butterflies: coloration matches predator's sensitivity

摘要

Unprofitable prey with conspicuous warning signals are often mimicked by other species, which then gain protection from predators. How closely two mimetic spe- cies resemble one another depends upon the visual perception of the signal recei- ver. However, most studies of mimetic coloration have been conducted using only the human visual system, which differs greatly from that of most animals. To bet- ter understand mimicry, we should study mimetic visual signals through the eyes of the intended receiver. Here, we use avian visual models to test predictions of putative Batesian mimicry in two Amazonian butterflies, Mimoides pausanias and Heliconius sara. We calculated Just Noticeable Differences (JNDs) and tetrahedral color volumes for 11 different patches: iridescent blue, yellow bars, red spots and black background. Several color patches were not visually discriminable for both avian visual systems (UV/VIS and V/VIS), and visual discrimination (i.e. degree of mimicry) of color patches depended upon the avian visual system. These two but- terfly species are more mimetic when viewed by their likely avian predators, which have V/VIS vision. Therefore, this mimetic assemblage may have evolved to be more spectrally accurate in the non-UV wavelengths which their avian predators are able to see. However, while many color patches of the two species were mod- eled to be difficult to discriminate, most color patches were not perfect matches regardless of visual system, and several patches were very poor mimics. Through this study we demonstrate the importance of testing putative mimetic assemblages using known predator perceptual models and lay a foundation for behavioral studies to further test mimicry in H. sara and M. pausanius.

標題：Prey from the eyes of predators: Color discriminability of aposematic and mimetic butterflies from an avian visual perspectives

摘要

Predation exerts strong selection on mimetic butterfly wing color patterns, which also serve other functions such as sexual selection. Therefore, specific selection pressures may affect the sexes and signal components differentially.We tested three predictions about the evolution of mimetic resemblance by comparing wing coloration of aposematic butterflies and their Batesian mimics: (a) females gain greater mimetic advantage than males and therefore are better mimics, (b) due to intersexual genetic correlations, sexually monomorphic mimics are better mimics than female-limited mimics, and (c) mimetic resemblance is better on the dorsal wing surface that is visible to predators in flight. Using a physiological model of avian color vision, we quantified mimetic resemblance from predators’ perspective, which showed that female butterflies were better mimics than males. Mimetic resemblance in female- limited mimics was comparable to that in sexually monomorphic mimics, suggesting that intersexual genetic correlations did not constrain adaptive response to selection for female-limited mimicry. Mimetic resemblance on the ventral wing surface was better than that on the dorsal wing surface, implying stronger natural and sexual selection on ventral and dorsal surfaces, respectively. These results suggest that mimetic resemblance in butterfly mimicry rings has evolved under various selective pressures acting in a sex- and wing surface-specific manner.

這篇的中心思想就想要測試三個假設 1) 雌性擬態的精確度比雄性好 2) 單型性擬態的比雌性擬態的物種精確 3) 擬態斑紋在背面的比在腹面的精確。作者想要知道這些現象是不是普遍存在於擬態的蝴蝶中，於是想說「如果從鳥類的視覺來看的話，會不會有差異呢？。」，就用了測量標本的反射光譜，得到某些數據，然後套入鳥類的視覺模型來看看這些擬態的蝴蝶會不會有差異。整個概念就是當把得到的數據套入模型後，比較model與mimic得到的結果，然後統計有沒有顯著差異。結果顯示雌性的擬態比雄性精確，雌性擬態與單型性的物種相比無差異，在背側斑紋比在腹側斑紋精確。

這個結果的確顯示了某些選汰壓力的作用方向，但這個文章中應該只是要展現這有某種演化趨勢，可是缺少考量某些多態型的物種（如大鳳蝶），或是不同的物種在自然界中行為的差異，或許會導向不同的結果與解釋。