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標題：Predator mimicry, not conspicuousness, explains the efficacy of butterfly eyespots

摘要

Large conspicuous eyespots on butterfly wings have been shown to deter predators. This has been traditionally explained by mimicry of vertebrate eyes, but recently the classic eye-mimicry hypothesis has been challenged. It is proposed that the conspicuousness of the eyespot, not mimicry, is what causes aversion due to sensory biases, neophobia or sensory overloads. We conducted an experiment to directly test whether the eye-mimicry or the conspicuousness hypothesis better explain eyespot efficacy. We used great tits (Parus major) as model predator, and tested their reaction towards animated images on a computer display. Birds were tested against images of butterflies without eyespots, with natural-looking eyespots, and manipulated spots with the same contrast but reduced resemblance to an eye, as well as images of predators (owls) with and without eyes. We found that mimetic eyespots were as effective as true eyes of owls and more efficient in eliciting an aversive response than modified, less mimetic but equally contrasting eyespots. We conclude that the eye-mimicry hypothesis explains our results better than the conspicuousness hypothesis and is thus likely to be an important mechanism behind the evolution of butterfly eyespots.

photo from Fig. 1

貓頭鷹蝶是常常用來解釋昆蟲眼紋的功用的例子，但是牠的眼紋到底是單純的眼紋還是跟真4的眼睛有一樣的功用，一直是個爭論不休的問題，加上前兩年有一篇文章說眼紋不是擬態眼睛，而單純是一種明顯的訊號，更讓貓頭鷹蝶的眼紋功用蒙上一層面紗。

原文標題：Lepidopteran wing patterns and the evolution of satyric mimicry

摘要 [原文網址]

The hypothesis of satyric mimicry postulates that the colour patterns of an animal may make its identity ambiguous, and this ambiguity interferes with the process of perception in vertebrate predators for a sufficient time to allow the potential prey to take evasive action. It has now been found that eyespots and other designs on the wings of many insect species are often coupled with other wing patterns and designs. These composite images often closely resemble heads and bodies of vertebrates (including birds and reptiles) and of various invertebrates. Such images can be perceived in living insects, although only rarely in set specimens because of displacement of the components. Visual processing by non-mammalian vertebrates generally involves attention to detail, suggesting that, at least initially, and unlike humans, they perceive embedded images on insect wings and bodies and ignore the whole or Gestalt. They are therefore likely to be confused by the ambiguity of the potential prey. It can be calculated that a delay of the order of only tenths of a second in the attack on a stationary insect by a predator could result in failure of capture. It is proposed in the present review that the concept of satyric mimicry be extended to include complex imagery of other organisms. Such iconic images, which often represent toxic or dangerous animals, are particularly common amongst saturniid moths and nymphalid and danaid butterflies (including the Monarch butterfly, Danaus plexippus). © 2013 The Linnean Society of London

這篇主要是在討論satyric mimicry這件事情，特別歸納了有關鱗翅目的相關研究，包含如何作用，不同類型捕食者的反應等。那麼，首要的問題應該是要先解釋什麼是satyric mimicry。

Satyric mimicry包含的擬態類型像是假頭假眼，或是像食蚜蠅這種不太像的擬態，都可以算是。首次被定義是在Howse & Allen (1994)這篇文章，意指「有點像什麼又不太像什麼」的不完美擬態，對於這個名詞目前找不到一個很好的翻譯，satyric這個字查到的意思都是性好酒色的(adj.)(明顯的跟這件事沒關係)，因此要給個中文名稱，或許可稱為「模稜兩可的擬態」。這個故事要從Dittrich et al (1993)的故事說起，這篇文章中用鴿子與食蚜蠅測試不完美擬態的實驗中，發現了鴿子可以分辨很像跟很不像的食蚜蠅，可是中間那些有點像又有點不像似乎就不太能分辨，可是鴿子對於這些東西的分辨時間變長了，因此Howse & Allen (1994)就認為這些不太像的擬態是「故意」的，用意在拖長捕食者的分辨時間，也就是增加自己的逃跑時間。

雖然這個理論被建立，但也不是每個人都同意。像是Sherratt (2002)中提到他認為satyric mimicry並不存在的一個原因是這個理論建立在族群的頻度上，但是不完美擬態的每個型頻度都不高，因此一個模稜兩可且頻度不高的斑紋是不太可能從天擇中存活下來的，而另一個可能是這些斑紋與擬態無關，單純的只是顯示牠們也不可食。

總之這些理論都還沒個結局，尤其是這種不完美擬態為什麼能夠存在，依然值得討論。