跳蛛的某些種類外觀看起來像蜂、螞蟻、或是有些像甲蟲，已經有許多的觀察與研究，但長得像蠅的似乎不太常見。這個研究描述了一個分佈於玻利維亞的跳蛛新種，其外觀的某些角度與幾種不同的蠅看起來十分相似，作者認為這可能是為了要靠近捕食這些蠅而形成的攻擊型擬態 (aggressive mimicry) Perger, R., & Rubio, G. D. (2018). A wolf in sheep’s clothing: The description of a fly resembling jumping spider of the genus Scoturius Simon, 1901 (Araneae: Salticidae: Huriini). PLOS ONE, 13(1), e0190582. http://doi.org/10.1371/journal.pone.0190582

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

大杜鵑 (Cuculus canorus) photo: Planet of Birds

標題：A shared chemical basis of avian host−parasite egg colour mimicry

摘要

Avian brood parasites lay their eggs in other birds’ nests and impose considerable fitness costs on their hosts. Historically and scientifically, the best studied example of circumventing host defences is the mimicry of host eggshell colour by the common cuckoo (Cuculus canorus). Yet the chemical basis of eggshell colour similarity, which impacts hosts’ tolerance towards parasitic eggs, remains unknown. We tested the alternative scenarios that (i) cuckoos replicate host egg pigment chemistry, or (ii) cuckoos use alternative mechanisms to produce a similar perceptual effect to mimic host egg appearance. In parallel with patterns of similarity in avian-perceived colour mimicry, the concentrations of the two key eggshell pigments, biliverdin and protoporphyrin, were most similar between the cuckoo host-races and their respective hosts. Thus, the chemical basis of avian host–parasite egg colour mimicry is evolutionarily conserved, but also intraspecifically flexible. These analyses of pigment composition reveal a novel proximate dimension of coevolutionary interactions between avian brood parasites and hosts, and imply that alternative phenotypes may arise by the modifications of already existing biochemical and physiological mechanisms and pathways.

Fig. 1 大杜鵑在匈牙利、芬蘭與捷克的蛋與當地寄主的相似度

大杜鵑 (Cuculus canorus) 是一種從內而外，從頭到尾都模仿其他物種的鳥類，成體的外觀類似某些雀鷹，牠們的鳥蛋能夠藉著擬態各種不同其他的鳥類的蛋，下在其他鳥類的窩裡，利用其他鳥類的資源來培養牠們的後代，其生活史幾乎可以說是寄生在其他鳥類的資源上，這個現象自然引起科學家對杜鵑濃厚的興趣，認為這無論是研究行為或演化，都是十分適合的生物模型。

這篇文章的作者群想討論一個問題：杜鵑的鳥蛋可以這麼相似，變化度又這麼大，是透過合成鳥蛋的化學機制控制，或是有什麼其他的機制控制呢？作者群取樣數種分佈在匈牙利、芬蘭與捷克的鳥種，其中有共域杜鵑的主要寄主、次級寄主與非寄主的鳥類，分析其鳥蛋表面的反射光譜與色素組成的化學結構，從光學與化學的角度推測杜鵑鳥蛋擬態的機制來源。

Fig. 2 光譜分析結果

Fig. 3 化學成分分析結果

結果發現杜鵑的蛋殼與當地寄主的蛋殼光譜有部分重疊，而杜鵑的蛋殼更廣泛的涵蓋到其他非寄主的蛋殼光譜。色素化學的分析結果顯示兩種主要形成蛋殼色素的化學物質，biliverdin與protoporphyrin，與當地寄主的蛋殼的濃度類似，顯示顏色的相似度可能來自色素化學物質濃度的趨同所導致。

大杜鵑 (Cuculus canorus) photo from ouse washes

標題：Hawk models, hawk mimics, and antipredator behavior of prey.

摘要

Prey typically respond to potential predators by taking flight. This results in an optimal flight initiation distance (FID) at which the risk of remaining and the cost of flight are equal. Thus, FID is strongly negatively correlated with susceptibility to predation by the sparrowhawk Accipiter nisus across species of small European birds. However, not everything that looks like a hawk is in fact a hawk. Aggressive mimicry arises from the resemblance between a dangerous model such as a predatory hawk and an innocuous mimic such as a cuckoo that makes errors made by individuals that encounter models and mimics potentially dangerous and life threatening. A prime example of such aggressive mimicry is the hawk-like appearance of common cuckoos Cuculus canorus and other cuckoos. If mimicry is efficient, we should expect that species of small birds that are prey of hawks and hosts of cuckoos react just as strongly to a cuckoo as to the presence of a dangerous model like a sparrowhawk. We used FID of small birds as a measure of the reaction of prey to models and mimics, predicting that FID would be negatively related to susceptibility to predation and positively to risk of cuckoo parasitism. Both susceptibility to sparrowhawk predation and rate of brood parasitism by the common cuckoo independently explained variation in FID, consistent with the expectation that both hawks and cuckoos have imposed significant selection pressures on FID and that species of small birds perceive cuckoos as true mimics of hawks.

獵物遇到天敵要逃跑的時候，通常會評估「到底要不要跑？」

覺得奇怪嗎？遇到天敵，先跑，就對了啊，難道還等天敵到面前了才傻傻的要跑嗎？

對於野外一天到晚被人盯著瞧，隨時可能被吃掉的物種來說，隨時隨地都可能遇到天敵，但不是隨時隨地都有力氣可以跑，如果太早跑反而提早被發現，因此這些物種會評估到底捕食者離我多近才要跑，這稱為flight initiation distance (FID)，也可以叫做初始逃跑距離，就是捕食者離我到多近的食後才開始逃跑。那麼為什麼會有這個距離呢？因為有些獵物身上有些隱蔽色或有些警戒色之類用來躲避天敵的機制，如果捕食者雖然靠的很近但其實沒發現，那麼就不用浪費力氣逃跑，可是相對的會遭遇非常高的風險：萬一被發現就跑不掉了。

雀鷹 (Accipiter nisus) photo from Eurasian sparrow hawk (wiki)

那麼有意思的事情就發生了。大杜鵑 (Cuculus canorus)眾所皆知，有把蛋下在別人的巢裡，讓別的鳥幫牠孵蛋的行為。有人覺得大杜鵑長的像雀鷹 (Accipiter nisus)，早期的科學家認為這是一種貝氏擬態，但後來發現有另一種可能：這些大杜鵑長的像雀鷹，把那些要幫牠孵蛋的鳥嚇走，大杜鵑就能順利的去這些鳥的巢裡下蛋了？

作者藉由測量那些幫忙孵蛋的小型鳥的FID來測試這件事。之前有研究顯示，歐洲的小型鳥的FID與感知捕食的壓力的平衡點是負相關（體型越小靠的越近），因此如果小型鳥感應到的是捕食壓力，那麼應該是負相關，如果感知到的是普通的杜鵑偷生蛋行為，則是正相關。大杜鵑看起來就像雀鷹的話，那麼小型鳥的FID應該會與看到雀鷹的FID結果相似。作者觀察了63種鳥類行為的結果顯示，雖然某些小型鳥對大杜鵑的反應就像對雀鷹一樣，但相較於捕食的壓力，對於認知「杜鵑來下蛋」這件事還是比較強烈，因此大杜鵑擬態雀鷹可能有侵略型擬態的作用，但作者還是認為這還是種貝氏擬態，功用可能在於寄生到比較兇的寄主時，不會被這些寄主反過來攻擊甚至喪命。綜合以上顯示兩種行為都帶給這些小型鳥不同的壓力，這使FID的測量與結果可能來自於更為複合的行為觀察才能解釋。

文中的擬態者 勞旦橫口鳚 (Plagiotremus laudandus) photo from Dianne J. Bray, 2011, Bicolor Fangblenny, Plagiotremus laudandus, in Fishes of Australia

文章中的被擬態者，金鰭稀棘䲁 (Meiacanthus atrodorsalis) photo: Dianne J. Bray, 2011, Eyelash Fangblenny, Meiacanthus atrodorsalis, in Fishes of Australia, accessed 31 Mar 2016

標題：Multiple selective pressures apply to a coral reef fish mimic: a case of Batesian-aggressive mimicry.

摘要

Mimics closely resemble unrelated species to avoid predation, capture prey or gain access to hosts or reproductive opportunities. However, the classification of mimicry systems into three established evolutionary mechanisms (protection, reproduction and foraging) can be contentious because multiple benefits may be gained by mimics, causing the evolution of such systems to be driven by more than one selective agent. However, data on such systems are generally speculative or anecdotal. This study provides empirical evidence that dual benefits apply to a coral reef fish mimic in terms of increased access to food (aggressive mimicry) and reduced predation risk (Batesian mimicry). Bicolour fangblennies Plagiotremus laudandus gained access to more reef fish victims, which they attack to feed on fins and scales, when they spent more time associated with their model Meiacanthus atrodorsalis. Furthermore, exact replicas of P. laudandus incurred fewer approaches from potential predators compared with control replicas that varied in resemblance to P. laudandus. Predators with trichromatic visual systems (three distinct spectral sensitivities) could potentially distinguish between replicas based on colour based on theoretical vision models. Therefore, this mimicry system could be best described as Batesian–aggressive mimicry in which mimicry evolution is driven by multiple simultaneous selective pressures.

photo from Fig. 1 a) i. 金鰭稀棘鳚 (Meiacanthus atrodorsalis) ii. 勞旦橫口鳚 (Plagiotremus laudandus) b) 三種手工實驗用假魚與控制組物種粗吻橫口鳚 (P. rhinorhynchos)

通常科學家會把牽涉擬態的物種歸類，譬如說這是貝氏擬態，那是穆氏擬態，也有可能是介於兩者間的負貝氏擬態，那麼會不會有一個物種同時牽涉兩種擬態的系統呢？

photo from Fig. 2 此圖說明model/mimic比例的高低與攻擊成功率無關（黑圈圈），但花在model旁邊時間越多，成功率較高（白鑽石）

photo from Fig. 3 左邊是捕食性魚類，右邊是非捕食性魚類 從上而下分別是三組：沒model/有mimic (Lizard island)，有model/有mimic (Lizard island)，有model/有mimic (Pulau Hoga)

photo from what-when-how

標題：Costs of Learning and the Evolution of Mimetic Signals.

摘要

Predators must use the appearance of their prey to decide whether it is likely to be defended. Most theory assumes that predators have completed learning about prey appearance, yet we do not understand how predators learn which aspects of appearance to use for classifying prey. If sampling prey can be risky, predators might forgo opportunities to learn about the relationship between prey appearance and defense. Using Bayesian inference and dynamic programming, we modeled how the immediate risks and future rewards of learning about prey appearance influence how predators learn. In addition, we explored how variation in predator learning affects the evolution of mimicry, which occurs when two prey evolve to share a common signal to predators. We found that when learning about prey with distinct appearances was expensive, optimal predators tended to lump them into the same category or exhibit an unwillingness to sample at all (neophobia). This resulted in a reduction in selection for defensive mimicry. However, the same predator behavior favored the evolution of aggressive mimicry, because in that case, mimics benefited from being sampled. When prey were very rare and costs of sampling them were high, predators exhibited neophobia, refusing to attack. This behavior could forestall the evolution of mimicry and instead select for polymorphism.

捕食者的學習對於警戒性/擬態的演化實在很重要，因為這是最主要的天擇來源，但科學家實在對捕食者的學習模式太不瞭解，主要的癥結點在於不知道捕食者什麼時候吃，什麼時候不吃，要幾次才學的起來，學的多快才能推動這些斑紋的演化，有多少心理學的因子牽涉在裡面，其中一種研究方法就是透過數學模型的模擬，來推估哪些因子可能牽涉其中。

擷取自文中的方程式

捕食者在面對具有警戒性/擬態訊號的獵物時，吃了，可能會拉肚子甚至喪命，不吃，浪費了難得可以得到能量的機會，在這中間捕食者時如何評估獲得(reward)與學習的消耗(cost)，這會如何對獵物產生影響，就是這篇文章所要探討的。作者評估了一些因子，建立了一些模型，跑了一些模擬（過程很複雜也很難，容我跳過），得到的結論是捕食者對於分辨兩個長的很像的東西的代價是非常昂貴的，可以想像一下，捕食者首先要先學到兩種獵物，如果是貝氏擬態，牠要分辨這個物種是不是能吃的那個，如果是穆氏擬態，要學到兩邊都不能吃，更別提如果環境中同時存在兩個系統，光在那邊學半天餓都餓死了。因此模擬出來的結果顯示，捕食者傾向把這類的獵物通通歸類於不能吃的那邊（也就是恐新症，neophobia），這就讓擬態的斑紋有演化的空間了。此外，作者發現侵略性擬態（aggressive mimicry）也有類似的趨勢。

標題：A complex mode of aggressive mimicry in a scale-eating cichlid fish

摘要

Aggressive mimicry is an adaptive tactic of parasitic or predatory species that closely resemble inoffensive models in order to increase fitness via predatory gains. Although similarity of distantly related species is often intuitively implicated with mimicry, the exact mechanisms and evolutionary causes remain elusive in many cases. Here, we report a complex aggressive mimicry strategy in Plecodus straeleni, a scale-eating cichlid fish from Lake Tanganyika, which imitates two other cichlid species. Employing targeted sequencing on ingested scales, we show that P. straeleni does not preferentially parasitize its models but—contrary to prevailing assumptions—targets a variety of co-occurring dissimilar looking fish species. Combined with tests for visual resemblance and visual modelling from a prey perspective, our results suggest that complex interactions among different cichlid species are involved in this mimicry system.

Mimicry systems are frequently categorized by the type of benefit gained by the mimic's resemblance to its model: protection from threat, including predation (protective mimicry), and increased access to resources, including prey items (aggressive mimicry). These category types may not be mutually exclusive, and some mimics may gain more than one type of benefit. Here we examined a contentious classic textbook example of mimicry between the cleaner wrasse Labroides dimidiatus and its mimic, the sabre-toothed blennyAspidontus taeniatus. We found that the benefit obtained by the sabre-toothed blenny varied between four geographical locations. At the Great Barrier Reef, in Indonesia and in the Red Sea, it rarely attacked reef fish victims, but instead relied on other food sources such as substrate items, damselfish eggs and tubeworms. Here, the main function of the mimicry system could be to protect the sabre-toothed blenny from predation (protective mimicry) and was consistent with a previous study in Japan. However, in French Polynesia, the sabre-toothed blenny aggressively attacked reef fish frequently, and potential victims were more likely to pose to solicit a cleaning interaction. Diet analysis from individuals in French Polynesia indicated material was gleaned from the surface of fish, including large pieces of fin, implying an increase in the benefits obtained from attacking reef fish (aggressive mimicry). This study provides a potential second example of a mimicry system in which multiple types of benefits are gained by a mimic, and importantly, that the benefits obtained by the mimic vary between different environmental conditions and/or geographical locations. This may have important implications for the maintenance and evolution of mimicry systems and may reflect different stages of an arms race with potential victims.