獵物警戒性的性狀變異是否會影響跳蛛捕食者的學習與記憶
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| 弓拱獵蛛 (Evarcha arcuata) photo from wikipedia |
標題：How variation in prey aposematic signals affects avoidance learning, generalization and memory of a salticid spider
摘要
Most studies of aposematism focus on the effect of warning signals on vertebrate predators, especially birds. In our experiments, we used jumping spiders, Evarcha arcuata (Araneae: Salticidae) as predators, and larvae of three colour forms (red, white, yellow) of an unpalatable firebug, Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae) as prey. The experiments were divided into four successive steps, focusing on different aspects of predatore-prey interaction. (1) When presented with a firebug for the first time, the spiders captured the white, least conspicuous colour form more often than the other two. No differences in the attack latencies were observed between the colour forms. (2) In the avoidance-learning test, the spiders were offered in succession five firebugs of one of the three colour forms. The attack and capture rate decreased in all colour forms, more notably in the red, most conspicuous form. (3) After five presentations of the same prey, the spiders were presented with a different firebug colour form. The results of the generalization process were asymmetric: spiders' attack rate increased when the red prey was followed by the yellow or white one, but decreased when the red form was presented after the other colour forms. (4) Spiders attacked the same prey more often the next day, but the attacks were seldom fatal. Similarly to the initial reaction, spiders captured the white firebugs more often. Our results show that for E. arcuata, the red coloration can represent an effective aposematic signal. Red prey coloration decreased the attack rate during the avoidance-learning process and favoured the prey in generalization between different colour forms. Yellow coloration was moderately effective against E. arcuata, whereas white coloration was the least effective because of low innate bias against this signal.
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| 無翅紅蝽 (Pyrrhocoris apterus) 紅色型 |
以行為實驗的設計捕食者對警戒色與擬態選擇的研究方法，是一個最直接了解在生態系中這些機制如何運作的方法。大多數的研究主要是以鳥類為實驗進行時的捕食者，是因為鳥類看起來對這類的獵物有明顯選擇，也被認為是推動擬態與警戒色的主要角色。然而，考慮到現實中有各式各樣的掠食生物，科學家也開始思考是否有能用其他動物來測試的可能性？
跳蛛在自然界是一個主要的捕食者，有些蛾的翅紋也與跳蛛擬態有關，但有關跳蛛的相關行為實驗卻很少。這個研究選擇以弓拱獵蛛 (Evarcha arcuata) 做為捕食者，以無翅紅蝽 (Pyrrhocoris apterus) 的三種色型-紅色、黃色與白色進行實驗。實驗分為四個部分 (1) 將跳蛛分為四組，分別是紅色、黃色、白色與果蠅做為獵物，結果發現對白色的捕捉率最高，但對所有色型的反該時間無顯著延遲； (2) 學習迴避測試：將其中一個色型的紅蝽連續給予同一隻跳蛛五隻，結果發現所有色型的捕捉率都逐漸下降，特別是最明顯的紅色；(3) 在給予五隻之後，給予不同色型，結果有趣的是如果一開始給的是紅色而後給白/黃色，跳蛛的攻擊率會上升，但如果是反過來的話，攻擊率會下降；(4) 跳蛛隔天對同樣獵物的攻擊較多，也同樣的對白色的獵物攻擊較多。這個結果顯示紅色對跳蛛而言是個有效的警戒色，黃色次之，白色效果最低。
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| 在給予五隻紅蝽的測試結果：攻擊率與捕捉率 三角=紅色，圓型=黃色，方型=白色，菱型=果蠅 |
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| 前五個給予紅-白與白-紅處理的結果 |
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| 前五個給予紅-黃與黃-紅處理的結果 |
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| 給予後三次與隔日的處理結果 |
這個研究的邏輯看似十分簡單，厲害的是他們的重覆數極多，每組的個體數都有25隻，加上每個子處理組，總共有200隻跳蛛。無論是要採200隻或是養200隻，若是考慮折損率，以跳蛛來說都是非輕易能達成的數量。另外，紅蝽的變異色也可能不容易取得，實際上來說這是很不容易的一個數量。而這類的行為研究也建議有這樣的重覆數才能有足夠的可信度。
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