[Article] 精靈箭毒蛙的擬態樣式分化與連續性種化現象

(copyright: Twomey et al. 2015)

標題：Mimetic Divergence and the Speciation Continuum in the Mimic Poison Frog Ranitomeya imitator

摘要 [原文]

While divergent ecological adaptation can drive speciation, understanding the factors that facilitate or constrain this process remains a major goal in speciation research. Here, we study two mimetic transition zones in the poison frog Ranitomeya imitator, a species that has undergone a Müllerian mimetic radiation to establish four morphs in Peru. We find that mimetic morphs are strongly phenotypically differentiated, producing geographic clines with varying widths. However, distinct morphs show little neutral genetic divergence, and landscape genetic analyses implicate isolation by distance as the primary determinant of among-population genetic differentiation. Mate choice experiments suggest random mating at the transition zones, although certain allopatric populations show a preference for their own morph. We present evidence that this preference may be mediated by color pattern specifically. These results contrast with an earlier study of a third transition zone, in which a mimetic shift was associated with reproductive isolation. Overall, our results suggest that the three known mimetic transition zones in R. imitator reflect a speciation continuum, which we have characterized at the geographic, phenotypic, behavioral, and genetic levels. We discuss possible explanations for variable progress toward speciation, suggesting that multifarious selection on both mimetic color pattern and body size may be responsible for generating reproductive isolation.

簡單的說一下這個故事的來由。

圖中左列的這個蛙蛙是個分佈在秘魯的一種箭毒蛙，中文名稱叫精靈箭毒蛙，這個蛙蛙很神奇的是個多態型，分別擬態右列四個位於不同棲地的物種，剛好這四個物種都在秘魯，而且剛好這四個物種都分佈在附近，這蛙蛙又剛好擬態這四個都在附近的物種。

這一切都這麼剛好不拿來做點什麼實在太可惜了。

所以什麼族群遺傳、野外調查、多態型分佈、雜交帶、選偶偏好之類的，想的到的可以做的其實都做了，現在的問題就在於：這樣的擬態型態分化會不會帶動種化？

於是這篇文章對於幾個不同型的雜交帶分別調查了中間型地理分佈的距離，族群是否基因交流，不同型態族群間的雄性是否有擇偶偏好等等。

在這裡我先說明，如果有種化現象的話，這些預期應該是中間型地理分佈的距離（也就是雜交帶）的空間應該很狹窄，族群間基因交流與滲漏的數值很低，雄性應該偏好選擇與自己相似的雌性，如此才有可能帶動種化。

結果說明中間型的地理分佈不一，從幾十公里到一百公里都有；族群間的基因交流值非常高；在雜交帶的雄性沒有偏好，可是在某些型態分佈中心的雄性有顯著的偏好。

結論上來說就是該有的都沒有，但這文章就抓了這點「在雜交帶的雄性沒有偏好，可是在某些型態分佈中心的雄性有顯著的偏好」來說明這是強烈的證據支持這族群正在連續性種化(speciation continuum)的開端，整篇文章唯一正面的證據就只有這個，其他大部分都只部分支持或看不出來族群間有明顯的分化，而且全文脈絡感覺就是為了要解釋這個現象而寫的，儘管只有一小部分的證據支持這現象。

所以各位同學看到了嗎，就算你的樹都沒解析度，族群都沒分化，但只要符合某些假設，你也可以說這就是種化的開端喔！

至於連續性種話這說下去太複雜了，有需求的話再看看要不要寫一篇來解釋一下。