有的紅火蟻種群只有一個蟻后，有的則有多個蟻后,，近日研究人員在紅火蟻體內(nèi)首次發(fā)現(xiàn)了決定社會行為的“社會型”染色體,，揭開了這一現(xiàn)象背后的遺傳學(xué)成因，也為紅火蟻防治提供了新思路,。
紅火蟻的種群有兩種類型,，一種嚴(yán)格只有一個蟻后，另一種擁有數(shù)百個蟻后,?？茖W(xué)家們發(fā)現(xiàn)，紅火蟻社會組織形式的差異是由一個具有“超基因”（supergene）的染色體決定的,，這一超基因包含六百多個基因,，具有兩種突變形式B和b，分別對應(yīng)紅火蟻社會的兩種類型。這項研究于一月十六日發(fā)表在Nature雜志上,。
為了解紅火蟻的社會組織形式,，研究人員對五百多只火紅蟻的基因組進行了分析。研究顯示,，染色體的B和b突變使其結(jié)構(gòu)產(chǎn)生差異,，與決定人類性別的X和Y染色體有點類似。如果火紅蟻種群中的工蟻只攜帶B,，它們就只接受單個BB蟻后,，但如果種群中有工蟻攜帶b它們就能接受多個Bb蟻后。
“這是一項驚人的發(fā)現(xiàn),，此前人們曾發(fā)現(xiàn)染色體結(jié)構(gòu)上的類似差異與蝴蝶翅膀圖案和人類癌癥有關(guān),，而這是首次發(fā)現(xiàn)決定社會行為的超基因，”文章共同作者,，倫敦大學(xué)瑪麗皇后學(xué)院的Dr Yannick Wurm解釋道,。
“現(xiàn)在，我們在火紅蟻中發(fā)現(xiàn)了決定社會形態(tài)的染色體變異,，這種特殊染色體可能也在其他物種中決定著行為等基礎(chǔ)特性,。”
當(dāng)繁殖季到來，兩種類型的年輕蟻后飛到空中與雄性交配,。隨后,，單蟻后種群的年輕蟻后會飛到較遠(yuǎn)的地方建立種群。這種社會模式能夠非常成功的入侵新領(lǐng)地,。其他年輕蟻后則加入近處已存在的多蟻后種群,。這些多蟻后種群產(chǎn)生的工蟻比單蟻后種群更多，因此在復(fù)雜環(huán)境更具優(yōu)勢,。
火紅蟻是源于南美洲的物種,，這種螞蟻的叮咬會使人如火灼傷般疼痛，火紅蟻的種群密度高且極富攻擊性,。上世紀(jì)三十年代火紅蟻偶然被引入美國南部,，從此逐步擴散到包括中國和澳大利亞在內(nèi)的許多地區(qū)?？刂苹鸺t蟻擴散的努力一直不太成功,，其拉丁名Solenopsis invicta正是“所向披靡”的意思。
Dr. Wurm補充道,，“我們的發(fā)現(xiàn)將有助于開發(fā)新的害蟲防治策略,。例如，可以利用殺蟲劑人工使社會型染色體上的基因失活,，使火紅蟻種群發(fā)生混亂,。”(生物谷Bioon.com)
doi:10.1038/nature11832
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A Y-like social chromosome causes alternative colony organization in fire ants
John Wang, Yannick Wurm, Mingkwan Nipitwattanaphon, Oksana Riba-Grognuz, Yu-Ching Huang, DeWayne Shoemaker & Laurent Keller
Intraspecific variability in social organization is common, yet the underlying causes are rarely known1, 2, 3. In the fire ant Solenopsis invicta, the existence of two divergent forms of social organization is under the control of a single Mendelian genomic element marked by two variants of an odorant-binding protein gene4, 5, 6, 7, 8. Here we characterize the genomic region responsible for this important social polymorphism, and show that it is part of a pair of heteromorphic chromosomes that have many of the key properties of sex chromosomes. The two variants, hereafter referred to as the social B and social b (SB and Sb) chromosomes, are characterized by a large region of approximately 13 megabases (55% of the chromosome) in which recombination is completely suppressed between SB and Sb. Recombination seems to occur normally between the SB chromosomes but not between Sb chromosomes because Sb/Sb individuals are non-viable. Genomic comparisons revealed limited differentiation between SB and Sb, and the vast majority of the 616 genes identified in the non-recombining region are present in the two variants. The lack of recombination over more than half of the two heteromorphic social chromosomes can be explained by at least one large inversion of around 9 megabases, and this absence of recombination has led to the accumulation of deleterious mutations, including repetitive elements in the non-recombining region of Sb compared with the homologous region of SB. Importantly, most of the genes with demonstrated expression differences between individuals of the two social forms reside in the non-recombining region. These findings highlight how genomic rearrangements can maintain divergent adaptive social phenotypes involving many genes acting together by locally limiting recombination.
