[Article] 穆氏擬態中的單向趨同：以重新檢驗祕魯北部箭毒蛙為例
摘要 [原文連結]
Whether the evolution of similar aposematic signals in different unpalatable species (i.e. Müllerian mimicry) is because of phenotypic convergence or advergence continues to puzzle scientists. The poison dart frog Ranitomeya imitator provides a rare example in support of the hypothesis of advergence: this species was believed to mimic numerous distinct model species because of high phenotypic variability and low genetic divergence among populations. In this study, we test the evidence in support of advergence using a population genetic framework in two localities where R. imitator is sympatric with different model species, Ranitomeya ventrimaculataand Ranitomeya variabilis. Genetic analyses revealed incomplete sorting of mitochondrial haplotypes between the two model species. These two species are also less genetically differentiated than R. imitator populations on the basis of both mitochondrial and nuclear DNA comparisons. The genetic similarity between the model species suggests that they have either diverged more recently than R. imitator populations or that they are still connected by gene flow and were misidentified as different species. An analysis of phenotypic variability indicates that the model species are as variable as R. imitator. These results do not support the hypothesis of advergence by R. imitator. Although we cannot rule out phenotypic advergence in the evolution of Müllerian mimicry, this study reopens the discussion regarding the direction of the evolution of mimicry in the R. imitator system.
箭毒蛙是一個關於警戒色很出名的例子，當然除了鮮豔的顏色外，跟南美洲原住民用箭毒蛙的神經毒抹在吹箭上也有關，而這也是中文翻譯的由來。大部分提到箭毒蛙大概都只會想到警戒色，而那些通常是只Dentrobates這個屬的類群，另一個類群就有些種類牽扯到擬態，也就是這篇文章所關注的類群，Ranitomeya，中文翻成精靈箭毒蛙，其實是一種台灣寵物市場也有在流通的寵物蛙。
R. imitator就是這篇文章的主角，這個在低地與高地的斑紋是不一樣的，在低地的種類是線條型的，被認為擬態R. ventrimaculata（上圖右邊），而高地型則是網紋型，被認為擬態R. variabilis（上圖左邊），在擬態的演化預測中，擬態群的產生通常是趨同(convergence)或是單向趨同(advergence)，而R. imitator因為分布廣泛，而且到處擬態不同的箭毒蛙，看起來有明顯的區域性，被認為是單向趨同的一個例子。
文中重新檢驗了這個單向趨同的假說，發現高低地的兩個model本來以為是不同種，結果發現這兩種還有基因交流，也就是應該是同一種，而且結果也顯示本來認為是model的物種分化時間居然比mimic還晚近，因此作者推論這個種不是比R. imitator還晚出現，就是分化還仍有頻繁的基因交流。
這個結果有趣的地方在於imitator其實斑紋變化非常的大，稍微搜尋一下就發現其實有很多的中間型，而ventrimaculata與variablis相對來說是區域性的穩定，因此imitator不被當成是model事情有可原；可是箭毒蛙其實是兩者都有毒，因此imitator被認為是model也無不可，且符合演化的預期，可是model，尤其是在穆氏擬態中，應該是要非常穩定的斑紋，而這與事實互相矛盾，因次需要更多的證據才能知道是怎麼回事。
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