[Article] 遺傳上有分化而擬態特徵並未改變：以毒蝶（Heliconius）為例

圖片來源：http://www.heliconius.net/wp-content/uploads/2012/04/770_timareta-ssp.jpg

原文標題：Genetic differentiation without mimicry shift in a pair of hybridizing Heliconius species (Lepidoptera: Nymphalidae)

摘要 [原文網址]

Butterflies in the genus Heliconius have undergone rapid adaptive radiation for warning patterns and mimicry, and are excellent models to study the mechanisms underlying diversification. In Heliconius, mimicry rings typically involve distantly related species, whereas closely related species often join different mimicry rings. Genetic and behavioural studies have n how reproductive isolation in many pairs of Heliconius taxa is largely mediated by natural and sexual selection on wing colour patterns. However, recent studies have uncovered new cases in which pairs of closely related species are near-perfect mimics of each other. Here, we provide morphometric and genetic evidence for the coexistence of two closely related, hybridizing co-mimetic species on the eastern slopes of the Andes, H. melpomene amaryllis and H. timareta ssp. nov., which is described here as H. timareta thelxinoe. A joint analysis of multilocus genotyping and geometric morphometrics of wing shape shows a high level of differentiation between the two species, with only limited gene flow and mixing. Some degree of genetic mixing can be detected, but putative hybrids were rare, only one of 175 specimens being a clear hybrid. In contrast, we found phenotypic differentiation between populations of H. timareta thelxinoe, possibly indicative of strong selection for local mimicry in different communities. In this pair of species, the absence of breakdown of genetic isolation despite near-identical wing patterns implies that factors other than wing patterns keep the two taxa apart, such as chemical or behavioural signals, or ecological adaptation along a strong altitudinal gradient.

毒蝶 (Heliconius)是一群分布在中南美洲的類尋，是穆氏擬態中最經典的例子，也是被研究最透徹的，從行為到基因體，到控制擬態特徵的基因已經通通被找出來了。

那麼這篇文章還要在探討什麼呢？

這篇文章討論的點非常細緻，要了解這篇文章的點，就要先說明一下毒蝶這個擬態群的概況。在以前，毒蝶的親緣關係剛出來的時候，大家意料之中的發現，所有長得像的，參與通一個擬態群的，都分屬在不同的支系，也就是參與同一個擬態群的親緣關係並不是最近的，而且這些斑紋是會推動種化的；但是後來又發現，原來也是有姊妹種參與同一個擬態群，而且兩種還能雜交交換基因，而這兩個種就是H. cydno與H. melpomene。

知道了這些後，再回到這篇文章，他們發現一個新亞種H. timareta thelxinoe，這個亞種是屬於H. cydno這個支系的，也就是說，理論上這個亞種應該會跟H. melpomene雜交才對，可是他們發現，與這個亞種共域的H. melpomene amaryllis雖然跟這個新亞種參與同一個擬態群，可是幾乎沒有基因交流，而在翅紋與翅形的型態分析中也發現這兩種其實已經分化有差異，而新亞種的不同族群也發現翅紋與翅形是有差異的（雖然看起來還是很像）。

就結論而言，這個研究群似乎認為在一對姊妹種而且會有基因交流的情況下，居然會出現型態與遺傳上的分化是不可思議的，最後他們並沒有很明確的討論是什麼原因造成，只說可能是某些行為或是生態上的原因造成這個結果。

然而我覺得奇怪的是，從他們的樹來看，H. timareta與H. cydno是同一個支系沒錯，但是這兩個種似乎都不是單系群，而且文中討論的兩個亞種也不是最近的兩個亞種，本來就不會有雜交好像不是太意外的結果，因此預設他們會雜交似乎有點太過，所以他們是否能以這個例子討論他們為什麼不雜交？

嗯.....有可能他們本來就不同種不會雜交啊。