Rampant karyotype evolution in jack jumper ants

人类的DNA由人体每个细胞中的23对染色体携带，而黑猩猩有24对染色体。有些鹿有三对，有些蕨类有600对。染色体数目如何以及为什么会随着进化时间的推移而变化一直是个谜。拥有不同数量的染色体可能会阻止不同的物种进行杂交，甚至会通过改变父母的基因被性别“洗牌”的程度来改变进化的速度。已知的任何物种的最小染色体数目也是可以想象到的最小的：1对，在跳跃蚂蚁Myrmecia croslandi中发现。这是一只体型较大、攻击性极强的澳大利亚蚂蚁，具有强大的刺痛力，偶尔还会致命。跳线蚁的不同寻常之处还在于，尽管它们在体型、外表和行为上非常相似，但近亲物种的染色体数量却大相径庭。我们是一个由中国研究人员领导的国际财团的成员，该财团目前正在用只有一对染色体的蚂蚁基因组进行测序，这是1000基因组计划的一部分，该计划的目标是到2012年完成500个动物基因组的测序和组装。来自Myrmecia croslandi基因组项目的数据将在明年内开始提供，预计在2011年底之前完成完整的基因组组装。一旦有了这些新的信息，我们就想用它来探索紧密相关的蚂蚁的基因组，这些蚂蚁的染色体要多得多；在一个案例中，多达18-32对。虽然我们知道蚂蚁有不同的染色体数目，但我们对组成这些染色体的基因组几乎一无所知。我们将通过估计不同物种的基因组大小和对第二个物种的基因组进行测序来解决这些问题，第二个物种的染色体比克罗斯兰迪分枝杆菌多得多，这样我们就可以问：染色体更多的蚂蚁总体上有更多的DNA，还是它们只是将相同数量的DNA分成更小的片段？染色体较多的蚂蚁是否有更多的“垃圾”DNA或重复DNA？我们还将开发可用于未来工作的方法，以确定不同染色体数量的蚂蚁是否可以进行杂交。蚂蚁是几乎所有陆地生态系统的高度多样化和重要组成部分，并表现出极其特殊的社会行为。我们的工作将增加对蚂蚁进化和多样性的了解，也将增加对其他物种的基因组和染色体进化的了解。

Human DNA is carried by 23 pairs of chromosomes in every cell of the body, while chimpanzees have 24 pairs. Some deer have three pairs, and some ferns have 600. How and why chromosome numbers change over evolutionary time has always been mysterious. Having different numbers of chromosomes may prevent separate species from interbreeding, or even change the rate of evolution by altering how thoroughly parents' genes are 'shuffled' by sex. The smallest known chromosome number for any species is also the smallest imaginable: 1 pair, found in the jack-jumper ant, Myrmecia croslandi. This is a large, highly aggressive Australian ant with a powerful, occasionally lethal sting. Jack jumper ants are also unusual in that very closely related species have widely different numbers of chromosomes despite being very similar in body size, appearance and behaviour. We are members of an international consortium, led by Chinese researchers, that is currently sequencing the genome of the ant with only one pair of chromosomes as part of the 1000 Genomes Project, which has stated aims to complete the sequencing and assembly of 500 animal genomes by 2012. Data from the Myrmecia croslandi genome project will start to become available within the next year and a full genome assembly is expected before the end of 2011. We want to use this new information as soon as it becomes available, to explore the genomes of closely related ants that have far more chromosomes; in one case as many as 18-32 pairs. Although we know that the ants have different chromosome numbers, we know almost nothing about the genomes that make up these chromosomes. We will address these issues by estimating the genome sizes for the different species and by sequencing the genome of a second species, with many more chromosomes than M. croslandi to allow us to ask: Do ants with more chromosomes have more DNA overall, or do they just divide the same amount into smaller pieces? Do ants with more chromosomes have more 'junk' or repetitive DNA? We will also develop methods which can be used in future work to determine whether ants with different chromosome numbers can interbreed. Ants are highly diverse and important components of almost all land ecosystems and show extremely specialised social behaviour. Our work will increase understanding of the evolution and diversification of the ants, and also of genome and chromosome evolution in other species.