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| photo from wongchunxing.com Myrmarachne Merotai （非本實驗中用種類） |
摘要
The jumping spider genus Myrmarachne (Salticidae) consists of over 200 species of morphologically accurate ant mimics, enabling Myrmarachne to evade ant-averse predators that confuse the spiders with ants (Batesian mimicry). A conspicuous but untested trait of Myrmarachne, which is frequently mentioned in the literature, is locomotory mimicry. For these spiders, locomotion that is more ant like than salticid like may be an integral part of the suite of mimetic signals. We quantified the locomotory pattern of several species of non-ant-like salticids, Myrmarachne, and ants from Australia. We found that the locomotion of the mimics generally resembles that of ants, but not of other salticids. To tease out the effects of locomotion from those based on morphology, ant-eating salticids as visual predators were presented with 3D animations of ant-like salticids walking either in ant or in salticid fashion. Ant-eating salticids spent significantly longer looking at the stimulus with ant-like movement and were significantly more likely to visually track and stalk the stimulus with ant-like movement. Overall, our results suggest that there is selection pressure on Myrmarachne for increased resemblance to a model by locomotor mimicry, despite the associated costs when faced with ant-eating predators.
蟻蛛屬 (Myrmarachne，跳蛛科)全世界超過200種，令人驚訝的是精確的擬態各種螞蟻的型態與行為，可能帶給這群跳蛛躲避其他天敵的好處，被認為是一種貝氏擬態。但令人疑惑的是，跳蛛科有另外一群種類是專吃螞蟻的，蟻蛛也可能被其他專吃螞蟻的跳蛛攻擊，這樣擬態螞蟻反而可能承受更大的風險，使得科學家一直想弄清楚這群蟻蛛到底是想怎樣？
雖然以人類的角度來看，蟻蛛看起來像螞蟻，走起來像螞蟻，可是有科學上的證據嗎？意外的不多，大部分是觀察式的證據，因此這篇文章的作者們想透過分析澳洲的蟻蛛與螞蟻的行為比較，還有為了弄清楚行為與型態對擬態的貢獻，也把蟻蛛的3D影像播放給吃螞蟻蜘蛛看，同時藉由科學上的行為分析與捕食者的觀點來分析，蟻蛛到底像不像螞蟻。
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| 實驗中觀察的種類之一，Myrmarachne smaragdina，Darwin， Female photo from Dr. Greg Anderson |
行為的紀錄分為三個類型：非螞蟻型跳蛛（其他跳蛛）、蟻蛛與螞蟻的行為模式，分析蟻蛛的行為究竟比較偏向普通的跳蛛，還是比較類似於螞蟻。行為的實驗則透過3D動畫建模，做出蟻蛛的型態，但行為分別是螞蟻與普通跳蛛的動畫，然後播放給吃螞蟻的跳蛛看（給蜘蛛看卡通的意思），分析蟻蛛究竟是透過行為或是型態來欺騙捕食者。
結果顯示蟻蛛的行為的確比較接近螞蟻而非像其他的跳蛛。吃螞蟻的跳蛛花了比較長的時間在螞蟻行為的蟻蛛影像上，顯示即使對捕食者來說，蟻蛛的行為也非常像螞蟻。因此總和來說，雖然偶爾可能面對來自吃螞蟻的蜘蛛的風險，蟻蛛的確受到某些未知的天擇壓力，迫使這樣精確擬態螞蟻的型態與行為留存。
Wrote by Chia-Hsuan Wei
