有幾個基因控制精靈箭毒蛙 (Ranitomeya imitator)的體色變化？
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| photo from Ecuatoria: Dendrobatids |
標題：Number of genes controlling a quantitative trait in a hybrid zone of the aposematic frog Ranitomeya imitator
摘要
The number of genes controlling mimetic traits has been a topic of much research and discussion. In this paper, we examine a mimetic, dendrobatid frog Ranitomeya imitator, which harbours extensive phenotypic variation with multiple mimetic morphs, not unlike the celebrated Heliconius system. However, the genetic basis for this polymorphism is unknown, and not easy to determine using standard experimental approaches, for this hard-to-breed species. To circumvent this problem,we first develop a newprotocol for automatic quantification of complex colour pattern phenotypes from images. Using this method, which has the potential to be applied in many other systems, we define a phenotype associated with differences in colour pattern between different mimetic morphs. We then proceed to develop a maxi- mum-likelihood method for estimating the number of genes affecting a quantitative trait segregating in a hybrid zone. This method takes advantage of estimates of admixture proportions obtained using genetic data, such as microsatellite markers, and is applicable to any other system where a phenotype has been quantified in an admixture/introgression zone. We evaluate the method using extensive simulations and apply it to the R. imitator system. We show that probably one or two, or at most three genes, control the mimetic phenotype segregating in a R. imitator hybrid zone identified using image analyses.
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| photo from content |
用來研究擬態系統的分類群中，除了毒蝶 (Heliconius)目前有系統的從生態到基因體，很少有例子能夠做到這種程度，主要是因為毒蝶好抓好生好養，可以容易的透過孟德爾式遺傳的方式找出性狀的變化，進而推估控制斑紋的基因數量、是否聯會(linkage)等遺傳上的資訊。很多其他的生物沒辦法做到這樣的研究，就是因為數量少難生難養，或是生活史世代太長，沒辦法進一步的探索這些資訊，進而推估背後的演化來源等等相關理論。
但科學家總是有辦法的。精靈箭毒蛙 (Ranitomeya imitator)是一種有多態性的物種，像毒蝶一樣，每一個不同區域的樣式都擬態當地的model，但箭毒蛙就是一個難生難養，難以取得大量子代的物種，這個研究就假設「如果一個基因控制能控制一種變異，那麼從透過分析表型的變異程度，應該可以知道到底有幾個基因控制這些表型」。作者透過把高解析度的照片弄成如上圖展示擬態的樣式，透過文中所寫的likelihood model，配上一些微衛星體的分子資料的比較，模擬究竟有幾種基因牽涉其中。
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| photo from content |
1) 只要透過照片就能分析，不需大量採集野外個體
2) 省去飼養的時間
3) 不需要花大錢全基因體定序就能有結果
這種模擬的結果，有點類似前測試，或是只能知道虛無假說的方向，提供一個推估同樣難生難養的分類群的遺傳資訊的方法，可是基因實際上有幾個，分佈在哪些染色體上，是否形成超基因 (supergene) ，對於演化的歷程有沒有影響，是無法從這個方法得知的。
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