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Change or die? Inconsistent decoration building in Argiope spiders
|關鍵字:||Decoration;隱帶;Visual signal;Argiope aemula;視覺訊號;長圓金蛛||出版社:||生命科學系所||摘要:||
動物會釋放視覺、嗅覺、聽覺等多樣化欺騙訊號去誘導其獵物或捕食者做出對其有利之行為來獲取最大利益，而當欺騙訊號廣泛地存在環境中，其不變及可預測性可能被訊號者識破，因而降低訊號釋放者本身的適存度。此篇研究將探究動物如何藉由改變欺騙訊號之頻度及樣式來解決此一困境。前人研究指出金蛛屬蜘蛛在其蛛網上所建構的白色絲狀隱帶 (Decoration) 是一種視覺欺騙訊號用以吸引獵物，但同時也會吸引捕食者前來。然而，野外觀察卻發現個體蜘蛛會改變隱帶的排列方式及出現的頻率。由於隱帶此種視覺訊號對於坐等型捕食者金蛛而言有著重要的覓食功能，我認為金蛛之所以有如此高度的隱帶變異是來自於獵物與捕食者雙方的壓力。前人研究顯示，訪花昆蟲會認知且學習具有相同形式的隱帶進而躲避位於特定位置的蜘蛛；而金蛛隱帶頻率及樣式的調整似乎是為了使昆蟲無法學習。本研究藉由操控隱帶的形式與頻率試圖解釋金蛛屬蜘蛛隱帶視覺訊號的不一致性是否為一種最佳化的生存策略。為方便操控，我利用長圓金蛛（Argiope aemula）及其隱帶為原型，製作在顏色訊號上與真實隱帶及蜘蛛相仿之色紙模型，於野外進行隱帶出現頻率與形式的交錯操控實驗，總共六種處理組，並利用攝影機記錄獵物與捕食者對不同處理組之反應。研究結果顯示隱帶形式改變或是不變的情況下，出現頻率越高能吸引越多獵物；而在不同頻率下比較隱帶形式改變與不變組發現，只有隱帶形式改變且密集出現才能有效地吸引獵物。此外，在隱帶形式不變時，出現頻率愈高則捕食者吸引率也隨之增加；然而一旦形式發生改變，則捕食者吸引率即會變低。此結果顯示金蛛屬蜘蛛建造密集且形式多變的隱帶的確有助於蜘蛛誘引獵物及混淆捕食者，似乎可證實隱帶的不一致性是一種提升覓食效率及降低被捕食風險的最佳化的訊號呈現策略。
Animals would convey visual, olfactory or auditory deceptive signals to mislead their prey or predators to act in ways that are beneficial to these signalers. However, when these deceptive signals are widely present in the environment their consistency and predictability may render them detected by receivers and consequently lower the fitness of the signalers. In this study, I investigated how animals change frequency and form of a deceptive signal to solve such problem. Previous studies showed that silk decorations built by Argiope spiders is a deceptive signal functioning to lure prey but at the cost of attracting unwelcome predators to the spiders simultaneously. Numerous field observations showed that the individual spiders would change the occurrence and arrangement of decoration bands on webs on a daily basis. Since the visually conspicuous decorations play a foraging role in this sit-and-wait predator, I hypothesize that pressures from prey and predators interplay to generate inconsistent web decorating behavior in Argiope spiders. Previous studies suggested that the pollinator insects may use consistent decoration form to avoid spider webs at a certain location and therefore changing decoration occurrence and form may lower the learning efficacy of insects. In this study I manipulated frequency and form of decorations by a dummy approach to evaluate whether Argiope spiders' inconsistent visual signaling is an optimal strategy. I used cardboards with chromatic properties similar to corresponding spider body color and decorations to construct dummies and the frequency and orientation pattern of dummy decorations were manipulated in the field. There were a total of six treatments and video cameras were used to monitor the responses of prey and predators to them. The results showed that no matter decoration form was variable or fixed those in high frequency group can attract more prey. When decorations occurred inconsistently and frequently insect attraction rate was the highest. Dummy decorations in high frequency group also attracted more unwelcome predators. However, when the decoration form varied the predator attraction rates decreased. These results imply that building decorations more frequently and inconsistently could help Argiope spiders to lure prey and mislead the predators simultaneously. My results thus demonstrate that inconsistent decoration building is an optimal signaling strategy for Argiope spiders.
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