有的红火蚁种群只有一个蚁后，有的则有多个蚁后，近日研究人员在红火蚁体内首次发现了决定社会行为的“社会型”染色体，揭开了这一现象背后的遗传学成因，也为红火蚁防治提供了新思路。
红火蚁的种群有两种类型，一种严格只有一个蚁后，另一种拥有数百个蚁后。科学家们发现，红火蚁社会组织形式的差异是由一个具有“超基因”（supergene）的染色体决定的，这一超基因包含六百多个基因，具有两种突变形式B和b，分别对应红火蚁社会的两种类型。这项研究于一月十六日发表在Nature杂志上。
为了解红火蚁的社会组织形式，研究人员对五百多只火红蚁的基因组进行了分析。研究显示，染色体的B和b突变使其结构产生差异，与决定人类性别的X和Y染色体有点类似。如果火红蚁种群中的工蚁只携带B，它们就只接受单个BB蚁后，但如果种群中有工蚁携带b它们就能接受多个Bb蚁后。
“这是一项惊人的发现，此前人们曾发现染色体结构上的类似差异与蝴蝶翅膀图案和人类癌症有关，而这是首次发现决定社会行为的超基因，”文章共同作者，伦敦大学玛丽皇后学院的Dr Yannick Wurm解释道。
“现在，我们在火红蚁中发现了决定社会形态的染色体变异，这种特殊染色体可能也在其他物种中决定着行为等基础特性。”
当繁殖季到来，两种类型的年轻蚁后飞到空中与雄性交配。随后，单蚁后种群的年轻蚁后会飞到较远的地方建立种群。这种社会模式能够非常成功的入侵新领地。其他年轻蚁后则加入近处已存在的多蚁后种群。这些多蚁后种群产生的工蚁比单蚁后种群更多，因此在复杂环境更具优势。
火红蚁是源于南美洲的物种，这种蚂蚁的叮咬会使人如火灼伤般疼痛，火红蚁的种群密度高且极富攻击性。上世纪三十年代火红蚁偶然被引入美国南部，从此逐步扩散到包括中国和澳大利亚在内的许多地区。控制火红蚁扩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补充道，“我们的发现将有助于开发新的害虫防治策略。例如，可以利用杀虫剂人工使社会型染色体上的基因失活，使火红蚁种群发生混乱。”(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.
