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When exploring forests of Central and South America it is common to stumble across highways of countless ants transporting large chunks of plant material. These are leaf-cutting ants, the dominant herbivores of the Neotropics, collecting leaves and flowers they feed to a fungus crop they cultivate in underground chambers.

这种共生在许多方面类似于我们自己的农业：蚂蚁迫在眉睫，依赖于食物的真菌，它们使用它们收集的材料施肥，甚至使用抗生素治疗真菌园疾病。

This mutualistic relationship has long drawn the attention of scientists trying to understand the evolutionary dynamics of cooperation between organisms across kingdoms of life. However, these ants are also fascinating because of their unique mating biology, and because the queens are extraordinarily long-lived.

Mating idiosyncrasies of leaf-cutting ants

A queen can live for two or three decades, during which she will never re-mate, but will prudently use the sperm from these males to fertilize millions of eggs.

Leaf-cutting ant queens mate during a single mating event early in adult life. When a queen embarks on a mating flight, she will mate with multiple male partners, and return to the ground to shed her wings and seek a suitable place to burrow a nest.

然而，虽然在将精子送到皇后之后，虽然雄性几乎立即下降，但一个女王可以住在两三十年中，在此期间，她永远不会重新伴侣，但会谨慎地使用这些男性的精子 - 储存在专门的器官中叫做spermatheca - 施肥数百万鸡蛋。

Such lengthy sperm storage represents a record in the animal kingdom, and creates an exceptional lifetime commitment between partners — it would be analogous to vertebrate females being constantly pregnant with sperm of a few males that need to be kept alive at ambient temperature and protected from senescence mechanisms for years after the male partners are dead and gone.

Since multiple males inseminate a leaf-cutting ant queen in a single afternoon, the spermatozoa of different males compete for storage in the queen spermatheca. This interplay between competition for storage and the need to remain alive for many years after storage has created unique evolutionary adaptations in ant sperm.

Unravelling reproductive conflicts in ants

Fertility research in vertebrates has firmly established that sperm are capable of responding to subtle changes in their surroundings, allowing them to reach and fertilize female eggs more effectively. These can be changes in pH, ion concentrations or temperature of reproductive tracts and glandular secretions, or the presence of specific molecules that attract sperm to fertilization sites.

通过调整通常用于脊椎动物研究中通常用于脊椎动物研究的精子运动的实验程序，我们发现蚂蚁精子能够做到同样的事情：不仅在与男性和女王生殖的分泌物接触时更加比例的精子会变得更快地游泳。器官，但他们根据这些分泌物是否属于自己，或者对皇后和竞争对手的男性不同。

We first noticed that when ejaculates from different males are mixed, sperm motility increases compared to when the same ejaculates swim individually. To identify the factors inducing these increases, we performed additional experiments by collecting sperm from a focal male and making them swim in seminal fluid from the same male, from a rival male, or in secretions from different compartments of the queen reproductive organs, as well as mixes of these various fluids.

我们发现，与盐水控制相比，用精子增强的盐水射精的精液流体，并且一旦这些精子与竞争对手且含量的流体的最精液接触，就进一步增加了动力。queen’s spermatheca.

从焦点精子的角度来看，靶雄性液体和女王精子液都是非自我组织的分泌物，我们得出结论，精子必须响应非自我分泌物中存在的分子，并相应调节动力 - 一种反应that makes sense when the presence of rival ejaculates means that racing for storage will increase a male’s reproductive success.

为什么精子在自己和外星人分泌物之间区分？

精子有可能成为最大的移动soon as they are inseminated in a queen, independently of the presence of any competing sperm, so why do they swim slower in their own seminal fluid? Expressing a recognition mechanism to differentiate between self and non-self is presumably costly, so our observations require an evolutionary explanation.

There may be a trade-off between the increased motility required to win the competitive race for storage and the long-term survival of sperm once they are in storage.

我们假设这种识别演变，因为维持精子运动能量昂贵并且导致活性氧（ROS）的产生。精子特别容易受到ROS产生的结构损伤，因为它们缺乏广泛的损害修复机制，这意味着ROS的任何增加可能导致精子施肥能力不可逆转的损失。

Thus, there may be a trade-off between the increased motility required to win the competitive race for storage and the long-term survival of sperm once they are in storage — important because it may be many years before they are used to fertilize eggs.

Data from multiple studies suggest ROS damage control is a key factor in maintaining sperm viability — queens of multiple ant and bee species upregulate anti-oxidative enzymes after sperm storage, and these enzymes are also abundant in their seminal fluid.

因此，在蚂蚁如何确保尽管昂贵的精子竞争时，进一步阐明了蚂蚁如何确保长期精子生存，未来的研究应该尝试更明确地测量与精子运动相关的ROS生产。