以掠食者捕食實驗評估球背象鼻蟲與擬硬象天牛間的擬態關係

Abstract

部分昆蟲使用物理性或化學性防禦策略以防止捕食者攻擊，同時以醒目的警戒訊號來嚇阻天敵。球背象鼻蟲具有癒合且堅硬的翅鞘，其翅鞘上的花紋也被認為具有警戒色的功能。與球背象鼻蟲共域分布的擬硬象天牛雖不具堅硬翅鞘保護，但擁有和象鼻蟲相似的花紋色彩與體型，長久以來被視為球背象鼻蟲的貝氏擬態者，然而此種擬態關係並未獲得實驗支持。為檢驗此假說，本研究以產於蘭嶼的斷紋球背象鼻蟲、條紋球背象鼻蟲和擬硬象天牛為獵物，並以斯文豪氏攀蜥為捕食者，釐清球背象鼻蟲與擬硬象天牛的擬態關係與翅鞘花紋的有效性。本研究提出四個假說: (1)對蜥蜴而言，擬硬象天牛的適口性可能較球背象鼻蟲高；(2)非共域的無經驗捕食者能在學習到模型物種的不可食經驗後，避免再次攻擊具有相似警戒訊號的擬態者 ; (3)與擬硬象天牛相比，條紋與斷紋球背象鼻蟲之間的相似性更高，其遭受蜥蜴攻擊的比例則更低；(4)斷紋球背象鼻蟲與擬硬象天牛的翅鞘花紋能作為有效的警戒訊號以抵禦有經驗的共域捕食者。結果顯示，無經驗的捕食者在習得有關斷紋球背象鼻蟲的難吃經驗後，後續攻擊條紋球背象鼻蟲和擬硬象天牛的比例顯著降低，支持了象鼻蟲和擬硬象天牛間的擬態關係。此外，兩種象鼻蟲間的擬態相似程度可能較斷紋球背象鼻蟲與天牛之間的更高。相比於僅有單次經驗的捕食者而言，有多次經驗的共域掠食者可能較有能力分辨具警戒性的模型與擬態者。最後，無花紋和有花紋的球背象鼻蟲與擬硬象天牛被共域捕食者攻擊的比例無明顯差異，兩種獵物可能藉由花紋、外型與移動姿勢等特徵作為警戒訊號，藉以抵禦蜥蜴捕食者。本研究驗證球背象鼻蟲和擬硬象天牛的擬態關係，並呈現由多重視覺線索組成的警戒訊號在昆蟲抵禦爬蟲類捕食者上的重要性。

Insects possessing physical or chemical defenses often display aposematic signal to deter predators. Pachyrhynchus weevils, which are protected by strong physical defense, can use bright coloration as an aposematic signal, and Doliops longhorn beetles have long been assumed to be Batesian mimics because they resemble Pachyrhynchus in coloration, appearance, and habitat. However, this putative mimetic relationship has never been experimentally verified. In this study, we tested this hypothesis using two weevils from Orchid Island, P. nobilis, and P. sonani, together with the longhorn beetles, D. similis, and use the agamid lizard, Diploderma swinhonis as the predators in behavioral experiments. We hypothesize that (1) D. similis is more profitable to lizards than the weevils; (2) allopatric naïve predators will learn to associate the shared coloration with unprofitability and subsequently avoid attacking prey bearing this coloration, indicating the effectiveness of mimicry; (3) P. sonani will experience a lower attack rate than D. similis because of its closer resemblance to the model P. nobilis yamianus; and (4) sympatric experienced predators will recognize the coloration of Pachyrhynchus weevils and Doliops longhorn beetles as an aposematic signal, thereby reducing predation risk. Our results support the existence of a mimetic relationship among these species. Naïve predators learn that P. nobilis yamianus was unprofitable, and subsequently reduced attacks on both P. sonani and D. similis. The resemblance between the two Pachyrhynchus weevils appeared to be stronger than that between the weevils and D. similis, consistent with differences in attack rates. In addition, predators appeared to use overall prey traits rather than elytral coloration alone when making foraging decisions. Sympatric predators with repeated foraging experience were better able to distinguish the model from its mimics. These findings provide experimental evidence for mimicry in the Doliops–Pachyrhynchus system and highlight the importance of multicomponent warning signals in predator discrimination