貝氏擬態的力量可以推動猩紅王蛇的生殖隔離
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| 左圖為有毒的珊瑚蛇，右圖為無毒擬態者猩紅王蛇 |
摘要
We evaluated whether Batesian mimicry promotes early-stage reproductive isolation. Many Batesian mimics occur not only in sympatry with their model (as expected), but also in allopatry. As a consequence of local adaptation within both sympatry (where mimetic traits are favored) and allopatry (where nonmimetic traits are favored), divergent, predator-mediated natural selection should disfavor immigrants between these selective environments as well as any between-environment hybrids. This selection might form the basis for both pre- and postmating isolation, respectively.We tested for such selection in a snake mimicry complex by placing clay replicas of sympatric, allopatric, or hybrid phenotypes in both sympatry and allopatry and measuring predation attempts. As predicted, replicas with immigrant phenotypes were disfavored in both selective environments. Replicas with hybrid phenotypes were also disfavored, but only in a region of sympatry where previous studies have detected strong selection favoring precise mimicry. By fostering immigrant inviability and ecologically dependent selection against hybrids (at least in some habitats), Batesian mimicry might therefore promote reproductive isolation. Thus, although Batesian mimicry has long been viewed as a mechanism for convergent evolution, it might play an underappreciated role in fueling divergent evolution and possibly even the evolution of reproductive isolation and speciation.
穆氏擬態的毒蝶 (Heliconius spp.)因為其環境的壓力（天擇）與自身的擇偶偏好（性擇），共同造就其不同區域的多態型，一些科學家認為不同的型態區隔或許可以是生殖隔離乃至種化的起源，也從早期的研究中找到部分的證據支持這個理論。然而因為擬態群特性的緣故，地理型態區隔不明顯等等，貝氏擬態或許也有一樣的現象，但支持的證據卻少之又少。
猩紅王蛇 (scarlet king snake, Lampropeltis elapsoides)與珊瑚蛇(coral snake, Micrurus fulvius)是新北區東南方著名的脊椎動物的貝氏擬態案例，可是自從被發現以來爭議不斷，主要是因為早期對於不太精確的擬態斑紋，以及有點無法解釋的分佈產生的疑惑，而近十年對於這個擬態群的研究我們對於這個擬態群又更瞭解了一些，包含猩紅王蛇的分佈其實比起珊瑚蛇來的廣，兩者分佈不重疊的區域擬態就就不精確，而造成這種分佈的原因可能來自廣域性的捕食者（猛禽）等等。這時候就產生疑問了，如果分佈共域/異域的型態不一樣，那有沒有可能像毒蝶那樣，有機會產生生殖隔離呢？
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| 作者使用的黏土模型，由上而下為共域型/雜交型/異域型 photo from Fig. 3 |
這個研究簡單的討論了這個問題，作者假設如果不同型態的族群無法進入不同的區域的話，不同型態的個體根本沒辦法遇見彼此，就會發生生殖前隔離(premating isolation)；而若是兩種型態在雜交帶產下中間型的個體，捕食者（天擇）不知道這是什麼就把牠吃了，那麼透過雜交帶的基因傳遞功能失效，就會產生生殖後隔離(postmating isolaiton)。作者用黏土做成三種不同的型態，分別是精確型/雜交型/不精確型，分別把這些型交叉測試，譬如把精確型放到異域的區域裡或者相反，測試這些型態的被攻擊率。
結果如同預期，不同型態在不同區域的確被攻擊的比率比較高，可是雜交型只有在共域的沙丘環境上被攻擊的比率比較高，其他環境統計上不顯著。因此作者認為，貝氏擬態的確有可能造成族群間的隔離（對雜交型來說，至少某些環境遭遇比較強的天擇壓力），進而造成生殖隔離乃至種化。
至於那個黏土模型.....好像挺微妙的？下次看作者會不會改成3D列印，搞不好做出來結果有差。
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