翡翠樹蛙對環境中聲音訊息之行為反應
No Thumbnail Available
Date
2019
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
訊息傳遞在兩棲類的繁殖中扮演非常重要的角色，不管是物種辨識、挑選配偶或建立領域，都仰賴從週遭環境中獲取並判斷不同形式的訊息，並依判讀的資訊做出進一步的決定。聲音訊號是無尾目物種最常用來傳遞訊息的模式，雄蛙於繁殖季節聚集至水邊，以鳴叫聲吸引雌蛙前來交配。然而，周圍同種及異種個體所發出的鳴叫聲，甚至自然環境產生的噪音，都對鳴聲的傳遞造成干擾。這些逆境對動物來說是必須克服的挑戰，並可能是促使物種演化的原動力。鳴叫對雄蛙而言是非常耗能的行為，在噪音干擾之下，雄蛙應該具有相對應的行為策略，減少訊號傳遞時受到的干擾，並提高鳴聲傳遞的成功率，以獲得繁殖的機會。不過相關研究多為人工環境下之測試，或探討人為活動所產生的噪音干擾，而在自然狀況下針對雄蛙對共域異種聲音訊號之行為反應實驗則非常缺乏。我的研究目的是了解雄蛙在繁殖季中如何克服噪音所造成的干擾，並且針對雄蛙”如何尋找適合鳴叫的地點”，以及”加入鳴叫集團後的策略”這兩個角度探討雄性翡翠樹蛙(Rhacophorus prasinatus)在噪音干擾下的行為策略。第1章首先探討環境中噪音的種類，以及前人研究中動物對噪音的因應方式。第2章則使用聲音回播的方式，測試雄性翡翠樹蛙對不同回播聲音的趨聲偏好(Phonotaxis preference)。有別於前人在室內進行短距離的研究，我模擬翡翠樹蛙在自然環境的實際尺度，建置一個直徑20公尺的試驗場地進行測試，並且檢測以下4個問題:（1）雄蛙偏好加入大型或小型的合唱集團？（2）雄蛙偏好加入高品質或低品質的鳴叫同伴？（3）雄蛙是否利用異種鳴聲定位潛在的繁殖地點？（4）雄蛙是否會加入或避開具有異種鳴聲的混種合唱集團？結果顯示，雄性翡翠樹蛙偏好加入大型的合唱集團；低品質的雄性翡翠樹蛙傾向於接近高品質的雄性翡翠樹蛙，這可能屬於衛星雄性的潛行(Sneak)行為；此外，在沒有同種叫聲的狀況下，雄性翡翠樹蛙會利用生態棲位差異較大的腹斑蛙(Babina adenopleura)的叫聲尋找潛在繁殖地點，但不會接近使用生態棲位相似的布氏樹蛙(Polypedates braueri)叫聲，這也代表雄性翡翠樹蛙有能力透過鳴聲辨識共域物種。第3章我同樣使用聲音回播的方式，以分析雄蛙鳴聲反應的差異，探討雄性翡翠樹蛙對背景噪音干擾的因應策略，並且檢測以下5個問題:（1）雄蛙是否能夠調整節奏或鳴叫時機以避免鳴聲與噪音重疊？（2）雄性對不同音頻(Hz)噪音的反應為何？（3）雄蛙是否會加入具有相同音頻噪音的合唱集團？（4）不同品質的雄蛙在高強度噪音干擾下是否採取不同的鳴叫策略？（5）野外實際狀況下雄蛙的鳴叫反應為何？結果顯示，雄性翡翠樹蛙會利用噪音發出的空檔調整其鳴叫時機，避免鳴聲與噪音重疊；雄性翡翠樹蛙顯著避免於與自身鳴聲主頻率(~1500Hz)相同的中頻噪聲(1000Hz-2000Hz)時段鳴叫，並避開具有這類噪音的合唱集團；雖然在測試期間所有雄蛙其鳴叫率(call rate)均顯著下降，推測可能是為了在噪音干擾下節省自身能量，然而，與高品質雄性翡翠樹蛙相比，低品質量雄性的鳴叫率降低程度更為明顯，這也代表面對噪音干擾時所採取之鳴叫策略可能與雄性個體的身體狀況有關。在最後一個章節中，我針對研究結果中未來可延伸的議題進行探討，包括:物種鳴聲的主頻率可能為影響物種共存的另一種資源型態；噪音干擾可能促進訊號的演化；雄蛙在無法預測雌蛙出現的狀況下，將能量投資於繁殖場的出席率和投資於鳴叫展示，可能是權衡(trade-off)下的結果；物種的趨聲行為可應用在物種保育，以及外來種移除措施。本論文的研究結果不僅提供了第一個模擬自然尺度下的測試案例，亦同時檢測多物種的掩蔽效應(mask effect)，並顯示在野外實際狀況下，蛙類的群集合唱行為可能為包含訊號傳遞、感官靈敏度、合唱團物種組成以及與競爭者之間敵我評估的綜合策略。
Acoustic communication plays a crucial role in the reproduction of most anuran amphibians, such as species recognition, mate choice and territory defense. For the species which aggregate in dense choruses, the high level of background noises would lead the frogs to face the interruption and further constrain their communication. Therefore, noise interference is a ubiquitous challenge for these animals. Signalers should behave to reduce masking by noise, and these strategies are presumably preferred by natural selection or sexual selection. The aim of my study was to explore how male frogs deal with background noises in the breeding season. By using broadcasting tests on a polyandrous choral treefrog Rhacophorus prasinatus, I examined how male frogs use conspecific and heterospecific signals to locate a chorus in Chapter 2 and tested the following questions: (1) Do male frogs prefer to join a large or a small chorus? (2) Do male frogs prefer to approach a high-quality or a low-quality male? (3) Do males utilize heterospecific calls to locate the potential breeding sites? (4) Do male frogs orient towards or avoid choruses containing heterospecific calls? My results indicated that male frogs prefer to join a large rather than small chorus. Low-quality males tend to approach high-quality males, which might be explained as the sneaking behavior of satellite males. Furthermore, male frogs may use heterospecific calls delivered by a noncompetitive sympatric species (a ranid frog) to find potential breeding sites, but not by a sympatric competitor (another rhacophorid frog) that occupies a similar niche. On the other hand, I further examined the response of males with the interference from background noise after join a chorus in Chapter 3, and aimed to answer the following questions: (1) Are male frogs able to adjust their tempo or call timing to avoid overlap with noise? (2) What is the response of males to noises with different frequencies? (3) Would male frogs choose to join or keep away from a chorus with too much noise interference? (4) Do males with different body conditions apply different strategies when facing high-intensity interference? (5) What is the strategy of males applied in the wild? The results indicated that male frogs adjusted their calling pattern by using the spacing of the noises to avoid a direct temporal overlapping and avoided medium-frequency noises which obviously overlapped their own signal after join chorus. Although all the frogs showed a significant decrease of call rates during broadcasting, possibly aiming to save their own energy; yet the level of decrease was more pronounced in low-quality males compared to high-quality ones. The results in my dissertation not only provided the first experimental test in natural condition which consider the multiple species masking effect in playback experiment, but also provided a guide for further approach, which should combine all relevant factors including signal transmission, sensory sensitivity, chorus joining decision, and alternative courtship strategy when testing the phonotaxis preference of anurans.
Acoustic communication plays a crucial role in the reproduction of most anuran amphibians, such as species recognition, mate choice and territory defense. For the species which aggregate in dense choruses, the high level of background noises would lead the frogs to face the interruption and further constrain their communication. Therefore, noise interference is a ubiquitous challenge for these animals. Signalers should behave to reduce masking by noise, and these strategies are presumably preferred by natural selection or sexual selection. The aim of my study was to explore how male frogs deal with background noises in the breeding season. By using broadcasting tests on a polyandrous choral treefrog Rhacophorus prasinatus, I examined how male frogs use conspecific and heterospecific signals to locate a chorus in Chapter 2 and tested the following questions: (1) Do male frogs prefer to join a large or a small chorus? (2) Do male frogs prefer to approach a high-quality or a low-quality male? (3) Do males utilize heterospecific calls to locate the potential breeding sites? (4) Do male frogs orient towards or avoid choruses containing heterospecific calls? My results indicated that male frogs prefer to join a large rather than small chorus. Low-quality males tend to approach high-quality males, which might be explained as the sneaking behavior of satellite males. Furthermore, male frogs may use heterospecific calls delivered by a noncompetitive sympatric species (a ranid frog) to find potential breeding sites, but not by a sympatric competitor (another rhacophorid frog) that occupies a similar niche. On the other hand, I further examined the response of males with the interference from background noise after join a chorus in Chapter 3, and aimed to answer the following questions: (1) Are male frogs able to adjust their tempo or call timing to avoid overlap with noise? (2) What is the response of males to noises with different frequencies? (3) Would male frogs choose to join or keep away from a chorus with too much noise interference? (4) Do males with different body conditions apply different strategies when facing high-intensity interference? (5) What is the strategy of males applied in the wild? The results indicated that male frogs adjusted their calling pattern by using the spacing of the noises to avoid a direct temporal overlapping and avoided medium-frequency noises which obviously overlapped their own signal after join chorus. Although all the frogs showed a significant decrease of call rates during broadcasting, possibly aiming to save their own energy; yet the level of decrease was more pronounced in low-quality males compared to high-quality ones. The results in my dissertation not only provided the first experimental test in natural condition which consider the multiple species masking effect in playback experiment, but also provided a guide for further approach, which should combine all relevant factors including signal transmission, sensory sensitivity, chorus joining decision, and alternative courtship strategy when testing the phonotaxis preference of anurans.
Description
Keywords
Alternative mating tactics, Calling strategy, Energy constraint, Honest signal, Noise masking, Resource partition, Satellite males, Alternative mating tactics, Calling strategy, Energy constraint, Honest signal, Noise masking, Resource partition, Satellite males