分子證據支持鳳蝶間性雙型性與限性擬態的獨立演化起源
 |
| 非洲白鳳蝶的多態型，左上方框內是雄性，線的上方是各種斑蝶與細蝶，線的下方是各型雌性白鳳蝶 photo from mimeticbutterflies.org |
標題：Independent evolution of sexual dimorphism and female-limited mimicry in swallowtail butterflies (Papilio dardanus and Papilio phorcas)
摘要
Several species of swallowtail butterflies (genus Papilio) are Batesian mimics that express multiple mimetic female forms, while the males are monomorphic and nonmimetic. The evolution of such sex-limited mimicry may involve sexual dimorphism arising first and mimicry subsequently. Such a stepwise scenario through a nonmimetic, sexually dimorphic stage has been proposed for two closely related sexually dimorphic species: Papilio phorcas, a nonmimetic species with two female forms, and Papilio dardanus, a female-limited polymorphic mimetic species. Their close relationship indicates that female-limited polymorphism could be a shared derived character of the two species. Here, we present a phylogenomic analysis of the dardanus group using 3964 nuclear loci and whole mitochondrial genomes, showing that they are not sister species and thus that the sexually dimorphic state has arisen independently in the two species. Nonhomology of the female polymorphism in both species is supported by population genetic analysis of engrailed, the presumed mimicry switch locus in P. dardanus. McDonald-Kreitman tests performed on SNPs in engrailed showed the signature of balancing selection in a polymorphic population of P. dardanus, but not in monomorphic populations, nor in the nonmimetic P. phorcas. Hence, the wing polymorphism does not balance polymorphisms in engrailed in P. phorcas. Equally, unlike in P. dardanus, none of the SNPs in P. phorcas engrailed were associated with either female morph. We conclude that sexual dimorphism due to female polymorphism evolved independently in both species from monomorphic, nonmimetic states. While sexual selection may drive male-female dimorphism in nonmimetic species, in mimetic Papilios, natural selection for protection from predators in females is an alternative route to sexual dimorphism.
 |
| 福翠鳳蝶 (Papilio phocas) 雄性 (上)與雌性 (下)， 另有一型與雄性相似 |
福翠鳳蝶 (Papilio phocas)與非洲白鳳蝶同屬白鳳蝶種群 (dardanus species-group)，有些觀點認為這兩種可能是最近緣的種類。福翠鳳蝶同樣是只有雌性多態型，但不同的是其不參與擬態。也就是說，如果系統發生學的分析支持這兩個物種是姊妹群，那麼就支持雌性多態性的單一起源。
這個研究以基因體層級大規模的分析，以3964個基因與全粒腺體序列推測這兩者間的親緣關係。結果顯示兩者並未如預期的是最近的姊妹群。另外，此團隊也對控制擬態斑紋的engrailed基因的單核苷酸多態性 (SNP, Single Nucleotide Polymorphism)做分析，在白鳳蝶的多態型族群中偵測到平衡選擇 (balancing selection)的特徵，而在單態型與福翠鳳蝶的族群中都沒有。在非擬態的福翠鳳蝶的SNP分析中，engrailed基因也與雌性多態無關。根據以上資料可以推論，這兩個物種的雌性多態性是起源於單態且非擬態的狀態獨立演化而來，進而形成性雙型性。非擬態的物種的性雙型性可能是由性擇推動，而擬態物種的性雙型性來自天擇作用於雌性，讓這兩個看似相似的現象有著截然不同的機制。
0 comments