郭公蟲總科的警戒性與擬態特徵的演化

photo from Cleridae (wiki)

標題：Aposematism and mimicry in soft-bodied beetles of the superfamily Cleroidea (Insecta)

摘要

The evolution of animal life strategies is among the main themes of current evolutionary biology. Checkered beetles, soft-winged flower beetles and their allies (superfamily Cleroidea), exhibit well-known aposematic colour patterns, particularly in the family Cleridae, which participate in mimicry complexes mostly with unpalatable beetles, ants and velvet ants representing a Mullerian–Batesian continuum. Many cleroids also exhibit attenuated hardening of cuticular layers resulting in a soft-bodied appearance. Here, a molecular phylogenetic analysis of the entire Cleroidea was performed using sequences of two nuclear and two mitochondrial loci of ~4 kb total length. Inferred phylogenies were used to reconstruct ancestral colour patterns and involvement in mimicry complexes. The hypothesis of a soft-bodied ancestor of Cleridae and allies was tested. The phylogenetic analyses corroborated the expanded Cleroidea concept including Byturidae and Biphyllidae formerly classified as Cucujoidea. Character state optimization showed cryptic col- oration was the ancestral state in Cleroidea, from which aposematic coloration originated several times in distant cleroid lineages. Within Cleridae, mimicry also arose from an ancestor that was cryptic, and multiple lineages that mimicked unpalatable beetles (Chrysomelidae, Meloidae, Lycidae) and stinging Hymenoptera evolved. Aposematic coloration was acquired in all major clerid lineages including Thanerocleridae, which are either the sister group of Chaetosomatidae or Cleridae. These findings suggest that mimetic traits in the clerid clade evolved at various times, possibly soon after the origin of soft-bodiedness. The adaptive value of aposematism in cleroids is likely to be enhanced in soft-bodied species, as this trait provides limited means of protection against predators, and therefore may promote the acquisition of aposematic and mimetic col- oration in various ecological situations.

郭公蟲 (Cleroids)是鞘翅目下的一個總科，全球約有3000種，從訪花到食腐肉的食性都有，有的郭公蟲還是飼料害蟲（如赤足郭公蟲）。這類群的外觀有的看起來像菊虎，有的看起來像葉蚤，有的看起來像螞蟻，說白了就是一個到處複製其物種斑紋的類群，可是這樣的斑紋演化是怎麼來的，其祖先是隱蔽色還是原本就有這些警戒色呢？郭公蟲的身體有硬有軟，這些硬的類群跟軟的類群各自獨立演化，或者這是一個各種不同的衍徵呢？

photo from content

作者用了兩個核基因（18S 與 28S的D2區域）與兩個粒線體基因（16S與cox1），大約4kb的長度來重建郭公蟲總科的親緣關係。細部的分類就不談了，特徵追溯的結果顯示郭公蟲總科的體色的祖徵應該是隱蔽色（82％），擬態螞蟻或其他甲蟲的特徵都是各自演化出來的。而軟/硬身體的類群則顯示郭公蟲總科的祖徵的身體是硬的而且有的是隱蔽色（97％）。這個演化關係似乎暗示軟身體的那群與演化出警戒色/擬態的關係比較緊密（軟身體群比較多與警戒色/擬態的類群），或許是因為身體柔軟受到捕食者（也就是天擇）的影響比較大，因此演化的方向朝著留下具有警戒色/擬態的類群。

photo from content

現在推測特徵演化大部分用MCMC的參數模型，這個研究也是，對於這個模型的使用沒什麼太大的意見，甚至可以說這種變動式的模型更適合計算演化特徵的改變，只是說這種方法算出來後，各個節上所呈現的是機率，這該如何解釋呢？該說那個共祖有x%的機會是A特徵，(1-x%)的機會是B特徵嗎？可是學生態的人很難理解這點，因為野外看到的特徵就是100%是某樣子（我這裡所說的不是野外族群的比例，那是另一個計算法了），不會因為時空背景有差異（有誰可以說說5%的機率看到某支蟲是紅色實際上應該是怎樣？一直在亂數閃爍嗎？）

我想，這就是薛丁格的貓吧。