Love amongst snails
春天已经到达英国，这对我们许多人来说意味着该是时候去我们的花园了。在这里，普通的花园蜗牛似乎只不过是害虫，而这是一个相当无趣的蜗牛。然而，这些显然简单的动物的行为可能是令人惊讶的复杂。
以他们的交配行为为例。花园蜗牛（Cornu aspermum）是同时的雌雄同体；也就是说，他们同时拥有男性和女性生殖器。人们可能会期望这会使性变得简单，两个参与者都想换精子来施肥。然而，蜗牛交配是复杂而脆弱的。
It begins as two snails approach each other and engage in an hours-long mating dance. During the dance each snail attempts to manoeuvre into position to fire its secret weapon in the mating game; a love-dart.
If the snail is successful, this dart – a sharp stylet of calcium carbonate – will be fired into the side of its mate, piercing its body wall. A snail’s love-dart is coated in mucus containing a cocktail of chemicals. Once these chemicals enter its mate’s blood stream they have a variety of affects, both physiological and behavioural, that increase the chances of the dart shooter’s sperm fertilising its mate’s eggs.
化学浪漫
为了更好地理解Love Dart的效果，我们需要检查蜗牛的生殖系统（请参见随附的图）。精子通过一条称为憩室的长隧道进入。精子必须穿过这里才能到达共产管，从那里可以使其进入中庭和精子储存器官，并有机会施肥。但是，交配管中的精子也可以吸入囊囊中并消化，没有受精的机会。
This sets up a mating conflict. Snails can mate multiple times, with several different ‘fathers’ fertilising each snail’s eggs. During mating, the sperm donor wants as much of their sperm as possible to reach the sperm storage organ to maximise the number of eggs they fertilise. For the sperm recipient however, it may be beneficial to have their eggs fertilised by multiple males. As such, they may not want all of their mate’s sperm to reach their eggs and will be happy for much of it to be lost in the diverticulum or digested in the bursa copulatrix.
成功部署的爱飞镖将鳞片转移到了精子捐献者方面。飞镖粘液中包含的化学物质增加了憩室中收缩的数量（假定精子的摄取更容易），并导致交配管中的收缩，从而减少了进入Bursa copulatrix入口的机会，并使精子不太可能被消化。所有这些意味着成功使用精子捐赠者的爱more than doubles its paternity伴侣的鸡蛋。
In a Japanese snail, the (curiously named) sought-after false hadra (Euhadra Quaesita），，，，the love-dart has also been found to导致伴侣的行为改变，减少他们愿意与其他蜗牛相处的意愿，从而增加使用蜗牛的精子施肥鸡蛋的可能性增加了飞镖的可能性。目前，目前尚不清楚其他蜗牛（例如花园蜗牛）在其他蜗牛中的广泛效果。
下面的视频（来自Lodil＆Koene 2016）显示了蜗牛生殖系统对从爱情末期获得的粘液的反应。
一个共同的交配策略？
Much of the previous research on the role of love-darts in snail mating took place in the lab of乔里斯·科恩（Joris Koene）在Vrije Universiteit Amsterdam in Holland. In new work,今天出版在BMC进化生物学，Koene的小组进一步阐明了Love Dart具有其影响的机制。
A considerable number of snail species, many close relatives of the garden snail, utilise love darts. The researchers aimed to determine if the love darts of these species, differing quite substantially in morphology (see figure), all work in the same way physiologically.
In a series of experiments, they injected mucus taken from the love darts of seven different snail species into the dissected reproductive tracts of garden snails. By videoing the reaction – in terms of number and intensity of contractions in the diverticulum and copulatory canal – they were able to determine if mucus from the varying species all had the same effect as mucus from the garden snail itself.
In general, it did; similar patterns of contractions were seen in each of the cross-species tests, especially in the copulatory canal. This supports the idea that these snail species use a common strategy of chemical manipulation with their love darts (although it’s possible the actual chemical compositions differ while producing broadly the same effects).
蜗牛的步调军备竞赛
What differences there were in response to the mucus of different snail species occurred in the diverticulum. These variations seem to be linked to variations in the presence and size of this organ in different snail species.
例如，来自F. fruticum没有憩室，对花园蜗牛憩室的影响相对较小。同样，当花园蜗牛憩室用其他四种蜗牛物种的粘液测试时，也可以看到小小的影响。
This supports the idea that the diverticulum has evolved as a defense against the manipulative effects of love-darts on sperm uptake in the copulatory canal. A longer diverticulum guards against this by increasing the number of contractions needed for sperm to make it to the copulatory canal. In turn, species with long diverticulums (like garden snails) have evolved an increasingly potent love-dart mucus as a counter-measure.
蜗牛似乎被锁定在正在进行的军备竞赛中。雄性改善了爱飞镖的效力，女性改善了针对这种策略的防御能力。每一个蜗牛都是男性和女性，攻击者和后卫，这使所有陌生人都成为一场军备竞赛。那些吃植物的蜗牛比我们想象的要复杂的生活更复杂的生活……
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