捕食者的受覺與北美蠑螈間體色的貝氏擬態與警醒程度的關係

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photo from Eastern newt (wiki), 貝氏擬態模型

photo from red-bakced salamander (wiki),其中一型非擬態

photo from Twan Leenders, 貝氏擬態者


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）？

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