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原文標題： Frequency-dependent variation in mimetic fidelity in an intraspecific mimicry system
[摘要] [原文網址]
Contemporary theory predicts that the degree of mimetic similarity of mimics towards their model should increase as the mimic/model ratio increases. Thus, when the mimic/model ratio is high, then the mimic has to resemble the model very closely to still gain protection from the signal receiver. To date, empirical evidence of this effect is limited to a single example where mimicry occurs between species. Here, for the first time, we test whether mimetic fidelity varies with mimic/model ratios in an intraspecific mimicry system, in which signal receivers are the same species as the mimics and models. To this end, we studied a polymorphic damselfly with a single male phenotype and two female morphs, in which one morph resembles the male phenotype while the other does not. Phenotypic similarity of males to both female morphs was quantified using morphometric data for multiple populations with varying mimic/model ratios repeated over a 3 year period. Our results demonstrate that male-like females were overall closer in size to males than the other female morph. Furthermore, the extent of morphological similarity between male-like females and males, measured as Mahalanobis distances, was frequency-dependent in the direction predicted. Hence, this study provides direct quantitative support for the prediction that the mimetic similarity of mimics to their models increases as the mimic/model ratio increases. We suggest that the phenomenon may be widespread in a range of mimicry systems.
本篇文章利用北美的豆娘 Nehalennia irene 進行實驗，這種豆娘是雄性單型性，雌性雙型性，而雌性的兩型中有一型是雄性型(andromorph)，另一種則為非雄性型(gynomorph)，而雄性型的相似度會隨著季節與族群有所變動。雄性型雌性有一個假說是雌性是為了避免增加不必要的雄性求偶次數，這篇文章的作者認為這樣的現象是種內擬態(intraspecific mimicry)。
根據以往的擬態理論，像是以珊瑚蛇為例，擬態者(mimic)的相似度與被擬態者(model)的數量與分布範圍有關係，因此作者們預測雌性雄性型(mimic)的相似度可塑性可能來自於雄性的數量(model)，當mimic/model比越高時，雌性雄性型也就會越像。作者們利用型質測量的方式評估其相似性，而結果顯示雄性型雌性在斑紋與尺寸都比其他型雌性更接近雄性，在雄性型雌性與雄性的相似度是與其相對頻度有正相關，也就是支持mimic/model比越高時，其相似度會越高。
雖然本篇沿用傳統擬態研究的定義，但與防禦性擬態所討論的問題仍有差異，以傳統定義來說，擬態這件事情所包含的是關於兩個以上的物種間的交互關係，而本篇討論的是種內關係；另外若與珊瑚蛇的例子比較，珊瑚蛇的結果是「被擬態者越多的地方，天擇可以容忍較不像的擬態者」，而本篇的結果則是「被擬態者越多的地方，擬態者越像」，雖然討論的系統不同，仍在「頻度」這個因子的討論上有所貢獻。
Wrote by Chia-Hsuan Wei
