在「如魔術般的特徵」背後，毒蝶還有什麼機制選擇配偶？
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| photo from Phillip's Natural World |
標題：Beyond magic traits: Multimodal mating cues in Heliconius butterflies
摘要
Species coexistence involves the evolution of reproductive barriers opposing gene flow. Heliconius butterflies display colorful patterns affecting mate choice and survival through warning signaling and mimicry. These patterns are called “magic traits” for speciation because divergent natural selection may promote mimicry shifts in pattern whose role as mating cue facilitates reproductive isolation. By contrast, between comimetic species, natural selection promotes pattern convergence.We addressed whether visual convergence interferes with reproductive isolation by testing for sexual isolation between two closely related species with similar patterns, H. timareta thelxinoe and H. melpomene amaryllis. Experiments with models confirmed visual attraction based on wing phenotype, leading to indiscriminate approach. Nevertheless, mate choice experiments showed assortative mating. Mon- itoring male behavior toward live females revealed asymmetry in male preference, H. melpomene males courting both species equally while H. timareta males strongly preferred conspecifics. Experiments with hybrid males suggested an important genetic component for such asymmetry. Behavioral observations support a key role for short-distance cues in determining male choice in H. timareta. Scents extracts from wings and genitalia revealed interspecific divergence in chemical signatures, and hybrid female scent compositionwas significantly associatedwith courtship intensity by H. timareta males, providing candidate chemical mating cues involved in sexual isolation.
對於穆氏擬態的毒蝶 (Heliconius)來說，因為大家長的都很像（從人類的角度來）那麼這些那麼像的蝴蝶在找尋配偶的時候會不會弄錯呢？一些早期的研究指出毒蝶可經由視覺來挑選配偶，並且會偏好與自己比較相像的個體交配。比較近期（2000後）的一些研究也指出，雖然人類看起來很像的毒蝶，但不同種間的色素來源是不一樣的，因此會有些微妙的差異，而不同種毒蝶的視覺正好可以辨識這些差異，降低找錯配偶的機會。
可是實際上不知道為什麼，就是會有些種類只要有點像就交配，又有些種類似乎很忠誠，而基因體的研究又告訴我們不同種/亞種/族群可能會雜交，那麼究竟背後還有什麼因素，能讓某些種分辨跟自己同種的個體呢？
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| 左為H. timareta ssp，右為H. melpomene amaryllis photo from La diversite des Heliconius |
結果顯示H. melpomene的雄性會同時偏好兩者，但H. timareta則強烈的只偏好同種的個體，即使是雜交的雄性後代也同樣支持這樣的偏好。H. timareta的求偶行為觀察中發現，雄性要接近雌性到很短的距離才會決定交配與否。從翅膀與生殖器取出費洛蒙的分析顯示這兩種間的化學訊號顯著的不同。雜交的雌性後代的費洛蒙組成明顯的會吸引H. timareta。這樣的結果支持除了透過視覺外，費洛蒙也扮演重要的角色。
雖然說鱗翅目昆蟲有複合式的求偶與種間辨識訊號也不是什麼大新聞，但透過遺傳學、化學生態學、行為學與生物統計學各種工具來更深入解析已知的資訊，這種跨界分析近來也成為討論擬態各種問題的趨勢。
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