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2011年8月26日 星期五

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。

2011年8月18日 星期四

毒蛺蝶的共域多態性擬態乃經由染色體重組維繫

文獻來源: Joron et al. (2011) Chromosomal rearrangements maintain a polymorphic supergene controlling butterfly mimicry. Nature doi:10.1038/nature10341

Abstract

Supergenes are tight clusters of loci that facilitate the co-segregation of adaptive variation, providing integrated control of complex adaptive phenotypes. Polymorphic supergenes, in which specific combinations of traits are maintained within a single population, were first described for ‘pin’ and ‘thrum’ floral types in Primula and Fagopyrum, but classic examples are also found in insect mimicry and snail morphology. Understanding the evolutionary mechanisms that generate these co-adapted gene sets, as well as the mode of limiting the production of unfit recombinant forms, remains a substantial challenge. Here we show that individual wing-pattern morphs in the polymorphic mimetic butterfly Heliconius numata are associated with different genomic rearrangements at the supergene locus P. These rearrangements tighten the genetic linkage between at least two colour-pattern loci that are known to recombine in closely related species, with complete suppression of recombination being observed in experimental crosses across a 400-kilobase interval containing at least 18 genes. In natural populations, notable patterns of linkage disequilibrium (LD) are observed across the entire P region. The resulting divergent haplotype clades and inversion breakpoints are found in complete association with wing-pattern morphs. Our results indicate that allelic combinations at known wing-patterning loci have become locked together in a polymorphic rearrangement at the P locus, forming a supergene that acts as a simple switch between complex adaptive phenotypes found in sympatry. These findings highlight how genomic rearrangements can have a central role in the coexistence of adaptive phenotypes involving several genes acting in concert, by locally limiting recombination and gene flow.

2011年4月14日 星期四

捕食者對車前燈蛾(Parasemia plantaginis)翅紋警戒色之方向性選擇及強度


Lindstedt C, Eager H, Ihalainen E, Kahilainen A, Stevens M, Mappesa J. (2011) Direction and strength of selection by predators for the color of the aposematic wood tiger moth. Behav. Ecol. doi:10.1093/beheco/arr017[full text]

簡介
在本篇研究中,作者以Parasemia plantaginis的雌性作為顯眼性獵物,該物種具有雌性多態型(紅/橘/黃三種翅紋色彩),以Galleria sp.作為隱蔽性獵物,並以pied flycatchers及Great tits作為捕食者進行了四個實驗:
(a) 同時提供顯眼性與隱蔽性獵物,去看在不同獵物下,捕食者的攻擊行為是否有差異;
(b)針對Para. plantaginis翅紋的差異及實驗背景,去進行色彩及亮度的標定,再去比較捕食者視神經的接收比率、製成模型比較;
(c)以兩種不同翅紋的Para. plantaginis去探討捕食者迴避學習的程度差異;
(d)於野外實驗探討捕食者對顯眼性獵物和隱蔽性獵物存活率的影響,以及紅色及橘色顯眼性獵物存活率上的差異。
結果發現:具警戒的顯眼性獵物較具有存活優勢,並且高度的對比色可以加快捕食者的迴避學習,但由於Para. plantaginis本身的化學防禦性物質的影響,使Para. plantaginis的雌性多態型於演化中得以保存,但本研究中所有數據於統計上均無顯著差異存在。

2011年3月8日 星期二

擬態的多種模式:偽裝的多態型會為隱避種帶來更多優勢

[ 圖片來源]

Skelhorn J & Ruxton GD. (2010) Mimicking multiple models: polyphenetic masqueraders gain additional benefits from crypsis. Behav. Ecol. 22: 60–65. doi:10.1093/beheco/arq166 [full text]

許多生物會藉由擬態無生命的物體來躲避天敵的攻擊,這個現象稱為偽裝(masquerade)。但偽裝的優勢會依被模仿者的數量和偽裝者的比例不同而不同,因此,當物種同時具有不同的多態型時可能是最有利的存在方式,例如:美國胡椒蛾(Biston betularia cognataria)幼蟲就是具有多態型的物種,其幼蟲取食樺木(birch trees)的會像樺木枝條,取食柳樹(willow trees)的就會長得像柳樹枝條。在此作者認為此幼蟲於不同寄主上所呈現的多態型是一種擬態行為,因此,作者以100隻小雞(Gallus gallus domesticus)作為捕食者,以120 *50*50 cm的籠子飼養,控制日照長度及溫度,並以黃粉蟲(Tenebrio molitor) 每天餵養兩次,以四齡的胡椒蛾幼蟲作為獵物,以樺木及柳葉飼養使幼蟲形成棕褐色及綠色兩種不同型式的幼蟲再進行實驗,實驗結果表明:捕食者會將幼蟲誤判為寄主枝條進而產生不捕食行為,但鳥類的行為可能是幼蟲本身的隱避色而非擬態,因此作者又測試了幼蟲的擬態是否成立,發現當幼蟲位於與自己相似的寄主上時,擬態效果是較為顯著的。同時,作者認為此研究也是首次說明物種的多態型對偽裝來說是有利的,並且有利於物種的隱避行為。

2010年8月23日 星期一

無翅紅蝽警戒色對捕食者的影響

文獻出處:
Exnerová, A., Svádová, K., Štys, P., Barcalová, S., Landová, E., Prokopová, M., Fuchs, R. & Socha, R. (2006) Importance of colour in the reaction of passerine predators to aposematic prey: experiments with mutants of Pyrrhocoris apterus (Heteroptera). Biological Journal of the Linnean Society 88: 143-153. [Full text]
Prokopová, M., Veselý, P., Fuchs, R. & Zrzavý, J. (2010) The role of size and colour pattern in protection of developmental stages of the red firebug (Pyrrhocoris apterus) against avian predators. Biological Journal of the Linnean Society 100(4): 890–898. [Abstract]

無翅紅蝽(Pyrrhocoris apterus)是半翅目(Hemiptera)昆蟲綱(Insecta)的物種,成蟲體長9-13 mm,發育過程中有五次蛻皮,可以借由蛻皮改變身上的斑紋,體色也可能隨著溫度變化而有些許改變。Alice Exnerová et al. (2006)於1999年至2002年間進行測試,探討無翅紅蝽警戒色的持久性問題、體色和背景色效應的關係,以及體色多態型的起源和警戒色的維持,他以大山雀(Parus major), 藍山雀(Cyanistes caeruleus), 歐亞鴝(Erithacus rubecula)和黑冠鶯(Sylvia atricapilla)作為捕食者,並且實驗過程中所使用的所有物種均於實驗前(一年內)捕獲,再經人工飼養而來。其結果得知,顏色的多態性可以說明:物種的演化是經由隱性突變所造成。

另外,無翅紅蝽成蟲和幼蟲雖然都具有紅色及黑色的體色,但體形大小、色彩和紋路相異,被捕食的頻率則有所差異。Milena Prokopová et al. (2010)假設體型大小會影響捕食者光化學信號的傳遞,而以大山雀(Parus major)和藍山雀(Cyanistes caeruleus)這兩種生態性相似的物種做為捕食者,來探討體型大小不同的鳥類,對無翅紅蝽的體型比例、顏色模式和捕食訊號之間關係的影響。結果顯示捕食者第一次遇到紅蝽時,體型不影響攻擊;但多次後,體型小的獵物較容易被攻擊、取食,並且獵物對兩種捕食者的保護信號有所不同(化學及光學信號),就連色彩模式也影響捕食者的意願,所以雖然幼蟲和成蟲同時具有紅色和黑色外表,但幼蟲的色彩並沒有提供良好的保護作用。

2009年9月21日 星期一

非洲白鳳蝶的系統發生學與擬態翅紋的演化

文獻出處:Clark, R. & Vogler, A. P. (2009) A phylogenetic framwork for wing pattern evolutio in the mimetic Mocker Swallowtail Papilio dardanus. Molecular Ecology 18: 3872-3884.

簡介
非洲白鳳蝶(Papilio dardanus)被認為是貝氏擬態(Batesian mimicry)中的擬態者(mimic),其雌雄二態性與雌性其中一型擬態大樺斑蝶(Danaus plexippus) 的表型長久以來被視為擬態生物學中的經典例子之一。本篇文章嘗試利用分子資料重建非洲白鳳蝶不同亞種間與不同區域間的親緣關係,嘗試找出其擬態斑紋的演化 時順。該研究使用兩個粒線體基因與數個與擬態斑紋有關或無關的核基因,重建不同亞種間的親緣關係。結果顯示粒線體基因在不同區域間呈現地理上的結構,並且 有較少的多樣性;而核基因間則無地理上的結構,並且基因序列間有多樣性的情形。定年的結果顯示,非洲白鳳蝶的種化約發生於2.9百萬年前,而擬態斑紋族群 的產生則在0.55-0.94百萬年前,擬態斑紋的產生在非洲白鳳蝶的原名亞種(P. d. dardanus)中是較早出現的,但仍晚於雌雄二態性。

Abstract
The Batesian mimetic swallowtail butterfly Papilio dardanus exhibits numerous distinct wing colour morphs whose evolutionary origins require large phenotypic shifts. A phylogenetic framework to study the history of these morphs was established by DNA sequencing of representative subspecies from sub-Saharan Africa and Indian Ocean islands. Two mitochondrial genes and the nuclear internal transcribed spacer marker revealed deeply separated eastern and western African mainland lineages, plus one lineage each on Madagascar and Grande Comore. These markers showed very little polymorphism within lineages. In contrast, markers genetically linked to the mimicry locus H, including the transcription factor invected and two adjacent amplified fragment length polymorphisms-derived sequences, showed high nucleotide diversity but were not geographically structured. Variation in the unlinked wingless gene showed a similar pattern, rejecting the hypothesis that high level of variation in the H region is due to balancing selection exerted by the phenotypes. The separation from a common ancestor with Papilio phorcas estimated at 2.9 Ma coincides with the origin of a mimicry model, Danaus chrysippus. However, the model reached Africa only at the time of the internal splits of P. dardanus mtDNA groups, here estimated at 0.55-0.94 Ma. The nuclear genome shows less geographic structure and may not track recent population differentiation, suggesting that widespread mimicry morphs have arisen early in the evolution of the P. dardanus lineage, although after the male-female dimorphism which is ancestral. The current wide distribution of P. dardanus and population subdivision evident from mtDNA may have been achieved only with the spread of the models across Africa.

2008年8月5日 星期二

[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