Rampant karyotype evolution in jack jumper ants

人体每个细胞中都有 23 对染色体携带人类 DNA，而黑猩猩则有 24 对。有些鹿有 3 对，有些蕨类植物有 600 对。随着进化时间的推移，染色体数量如何以及为何发生变化一直是个谜。拥有不同数量的染色体可能会阻止不同物种的杂交，甚至通过改变父母基因被性别“洗牌”的彻底程度来改变进化速度。对于任何物种来说，已知的最小染色体数也是可以想象到的最小染色体数：在跳跳蚁 Myrmecia croslandi 中发现了 1 对。这是一种体型巨大、攻击性极强的澳大利亚蚂蚁，其蜇伤力强大，有时甚至致命。杰克跳蚁的另一个不同寻常之处在于，尽管它们的体型、外观和行为非常相似，但亲缘关系非常密切的物种却拥有截然不同的染色体数量。我们是一个由中国研究人员领导的国际联盟的成员，该联盟目前正在对只有一对染色体的蚂蚁进行基因组测序，作为千个基因组计划的一部分，该计划表示目标是到 2012 年完成 500 个动物基因组的测序和组装。来自 Myrmecia croslandi 基因组计划的数据将在明年开始提供，预计在 2011 年底之前完成完整的基因组组装。我们希望使用这一新方法一旦获得信息，就可以探索具有更多染色体的密切相关蚂蚁的基因组；在一种情况下多达 18-32 对。尽管我们知道蚂蚁有不同的染色体数目，但我们对构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并对第二个物种的基因组进行测序来解决这些问题，该物种的染色体比M. croslandi多得多，以便我们可以问：拥有更多染色体的蚂蚁总体上是否有更多的DNA，或者它们只是将相同数量的DNA分成更小的片段？拥有更多染色体的蚂蚁是否有更多的“垃圾”或重复DNA？我们还将开发可在未来工作中使用的方法，以确定具有不同染色体数目的蚂蚁是否可以杂交。蚂蚁是几乎所有陆地生态系统的高度多样化且重要的组成部分，并表现出极其专业的社会行为。我们的工作将增进对蚂蚁的进化和多样化以及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.