穿越生死的山谷：適存度起伏與穆氏擬態多態型的關聯
 |
| Fig. 1 實驗區域與實驗中所使用的表型 Hom. 同型合子 Het. 異型合子 exotic 非本地型 |
摘要
Characterizing fitness landscapes associated with polymorphic adaptive traits enables investigation of mechanisms allowing transitions between fitness peaks. Here, we explore how natural selection can promote genetic mechanisms preventing heterozygous phenotypes from falling into non-adaptive valleys. Polymorphic mimicry is an ideal system to investigate such fitness landscapes, because the direction of selection acting on complex mimetic colour patterns can be predicted by the local mimetic community composition. Using more than 5000 artificial butterflies displaying colour patterns exhibited by the polymorphic Mullerian mimic Heliconius numata,we directly tested the
role of wild predators in shaping fitness landscapes.We compared predation rates on mimetic phenotypes (homozygotes at the supergene controlling colour pattern), intermediate phenotypes (heterozygotes), exotic morphs (absent from the local community) and palatable cryptic phenotypes. Exotic morphswere significantly more attacked than local morphs, highlighting predators’ discriminatory capacities. Overall, intermediates were attacked twice asmuch as local homozygotes, suggesting the existence of deep fitness valleys promoting strict dominance and reduced recombination between supergene alleles. By including information on predators’ colour perception, we also showed that protection on intermediates strongly depends on their phenotypic similarity to homozygous phenotypes and that ridges exist between similar phenotypes, which may facilitate divergence in colour patterns.
在先前的導讀中提到，控制穆氏擬態的毒蝶 (Heliconius) 斑紋基因的顯性性狀比較佔有優勢，中間型或隱性性狀能控制斑紋的機會相對減弱，而顯隱性與中間型又分別代表同型合子 (homozygous) 與異型合子 (heterozygous)，雖說遺傳結構支持顯性性狀比較容易表現，可這畢竟是實驗室內觀測到天擇的結果，在已經知道超基因的控制與顯隱性的優勢後，再次回到野外的話，這些斑紋的適存度 (fitness)又會有什麼樣的故事？
這篇研究就在討論我們已經知道穆氏擬態的毒蝶具有多態型，而且不同區域的多態型的遺傳結構各有不同，顯隱性表現也有各自的差異，但這是因為遺傳結構的限制，或是自然環境中天擇的影響，控制某些基因型的選汰還不清楚，在已經知道這麼多的基因體結構與其跟天擇連結的推測後，作者群再次把故事拉回野外實驗室中，測試天擇比較偏好同型或異型合子。
作者群依據Heliconius numata不同區域的型態，分別放置同型、中間型與非本地型的人工蝴蝶到野外環境中，總共放了超過5000隻的樣本到野外中，經過三天後回收樣本，檢查是否有U型或V型的攻擊痕跡，必且根據對應的形狀判斷是來自哪種捕食者的攻擊。
 |
| Fig. 2 不同表型的被攻擊次數，顯示中間型與非當地型被攻擊次數顯著較高 BB aa 同型合子 Ba 異型合子 exotic 非本地型 |
 |
| Fig. 3 不同表型在各種視覺模式下的關聯性 |
<<相關閱讀>>
0 comments