為何車前燈蛾的翅紋多樣性可以長期存在？

[image]
Nokelainen O, Hegna RH, Reudler JH, Lindstedt C, Mappes J. 2011. Trade-off between warning signal efficacy and mating success in the wood tiger moth. Proc. R. Soc. B. doi: 10.1098/rspb.2011.0880 [full text]

從演化的觀點來看，特徵選汰應傾向於對物種存活有利的方式，並且，後期這些基因特質應達到穩定且妨礙多態型的存在，但有許多警戒色的例子顯示多態型的物種是可以同時存在於相同族群中，其顯示不同型態之特徵可能具有不同優勢存在，或其可能具有相同功效。在此，作者以具有明顯翅紋變異的白色及黃色車前燈蛾(Parasemia plantaginis)作為獵物，以藍山雀(Parus caeruleus)作為捕食者測試翅紋警戒色在存活率和繁殖成功率之間的關係。結果顯示：(a)捕食者對於黃色翅紋有較長的攻擊延遲時間 (b)黃色翅紋的個體存活率比白色翅紋的個體好 (c)白色翅紋的個體繁殖成功率比黃色翅紋個體好，因此，作者認為此結果正好為車前燈蛾白色及黃色翅紋同時共存於自然界作一個很好的解釋。

演化的軍備競賽─紅皇后與有性生殖

程樹德(2010) 紅皇后與有性生殖。PanScience。http://pansci.tw/archives/3745

作者於短短的一文中敘述了幾件事：
a. 范華倫(Leigh van Valen)於化石堆中悟出”紅皇后假設”：「表示物種必須不斷演化，才能在競爭中保持現有地位，不致於被競爭者淘汰」
b. 有性生殖的優勢在於造成個體基因的重新排列組合，使族群位於不斷變動的環境中有存活下來的機會，或者也能藉此刪除因突變而產生的壞基因；反之，無性生殖無法去除壞基因，甚至可能將其累積，而此稱為穆勒撐高機(Muller’s ratchet)理論。
c. 彩票理論(lottery principle)：無性生殖如同購買大量同號碼的彩票，而有性生殖如同買少量但號碼均不同的彩票，兩者相比時，前者中獎的獲益較高，但是後者中獎的機率則比前者高。
d. 一個共同研究，以病毒與細菌的共同演化實驗表明：兩物種在共演化下，其演化速率會比單獨演化要來得快，此結果則支持范華倫的軍備競賽假說。

總結：自然界的物種多以共演化的方式進行軍備競賽，而有性生殖則為其中一種使族群於競賽中增加存活機會的方式。

棲地分割是否導致擬態的毒斑蝶亞科種類的分化？

photo from http://www.ucl.ac.uk/taxome/jim/Mim/moth.html

source: Hill RI. (2010) Habitat segregation among mimetic ithomiine butterflies (Nymphalidae). Evol. Ecol. 24: 273-285. [abstract]

簡介
擬態生物學家對於共棲並擬態蝴蝶的翅紋多樣性，抱持著讚嘆卻無法有合理的解釋，因為在天擇的作用下，捕食者對於擬態的斑紋的選汰，應該會迫使捕食者採用同樣的斑紋以加強擬態的效應。擬態群間的棲地分割是一個已經用來測試的假說，且可能可以用來解釋擬態群的高多樣性，但截至目前為止，以這個假說來討論擬態群的分化的研究仍然很少。本篇基於這個假說，測試不同的擬態群是否限定在特定的棲地中。作者取樣分布自厄瓜多的毒斑蝶亞科中9個不連續的擬態群且分屬於4種不同的棲地。毒斑蝶亞科的種類與數量在開放式棲地都是最少的，棲地的偏好性也在大多數的種類被觀察到。不同的擬態群間的棲地有顯著的不同，顯示不同的棲地是維持擬態群多樣性的重要因素。然而，仍然觀察到擬態群的分佈有重疊的情況，特別是在2個數量最多的擬態群中。這樣的分佈格局是被較為普遍的種類所驅動，而稀有種類與數量較多種類的分布僅有較薄弱的證據顯示其符合。因此，棲地分割在擬態的多樣性的演化中，僅對於數量較多的model有其貢獻，但這個因子對於整體演化的影響度可能比起其他的因子薄弱。

[Article]Mimetic butterflies support Wallace's model of sexual dimorphism

Mimetic butterflies support Wallace's model of sexual dimorphism
Proc Biol Sci. 2008 Jul 22;275(1643):1617-24.
Krushnamegh Kunte

Section of Integrative Biology, University of Texas at Austin, 1 University Station C 0930, Austin, TX 78712-0253, USA Theoretical and empirical observations generally support Darwin's view that sexual dimorphism evolves due to sexual selection on, and deviation in, exaggerated male traits. Wallace presented a radical alternative, which is largely untested, that sexual dimorphism results from naturally selected deviation in protective female coloration. This leads to the prediction that deviation in female rather than male phenotype causes sexual dimorphism. Here I test Wallace's model of sexual dimorphism by tracing the evolutionary history of Batesian mimicry—an example of naturally selected protective coloration—on a molecular phylogeny of Papilio butterflies. I show that sexual dimorphism in Papilio is significantly correlated with both female-limited Batesian mimicry, where females are mimetic and males are non-mimetic, and with the deviation of female wing colour patterns from the ancestral patterns conserved in males. Thus, Wallace's model largely explains sexual dimorphism in Papilio. This finding, along with indirect support from recent studies on birds and lizards, suggests that Wallace's model may be more widely useful in explaining sexual dimorphism. These results also highlight the contribution of naturally selected female traits in driving phenotypic divergence between species, instead of merely facilitating the divergence in male sexual traits as described by Darwin's model.
Keywords
Batesian mimicry, polymorphism, female-limited mimicry, directional selection, stabilizing sexual selection, convergence

[Article]Conflict btw natural & sexual selection due to mmicry

Interspecific sexual attraction because of convergence in warning colouration: is there a conflict between natural and sexual selection in mimetic species?

Journal of Evolutionary Biology

Volume 21 Issue 3 Page 749-760, May 2008

Citation: C. ESTRADA, C. D. JIGGINS (2008) Interspecific sexual attraction because of convergence in warning colouration: is there a conflict between natural and sexual selection in mimetic species? Journal of Evolutionary Biology 21 (3) , 749–760 doi:10.1111/j.1420-9101.2008.01517.x

Abstract

When species converge in their colour patterns because of mimicry, and those patterns are also used in mate recognition, there is a probability of conflicting selection pressures. Closely related species that mimic one another are particularly likely to face such confusion because of similarities in their courtship behaviour and ecology. We conducted experiments in greenhouse conditions to study interspecific attraction between two mimetic butterfly species, Heliconius erato and Heliconius melpomene. Both species spent considerable time approaching and courting females of the co-mimic species. Experiments using wing models demonstrated the importance of colour pattern in this interspecific attraction. Although males of H. melpomene were attracted to their co-mimics as much as to their own females, H. erato males were more efficient at distinguishing conspecifics, possibly using wing odours. Although preliminary, these results suggest that the use of additional cues may have evolved in H. erato to reduce the cost of convergence in visual signals with H. melpomene. Overall, our results showed that there might be a cost of mimetic convergence because of a reduction in the efficiency of species recognition. Such cost may contribute to explain the apparently stable diversity in Müllerian mimetic patterns in many tropical butterfly assemblages.