Trematode Solider（左）攻击更大的生殖形式（右）。学分：瑞安·赫辛格（Ryan Hechinger）

Caste formation and how it works

The allocation of specific jobs to individuals and the co-operative division of labour within a colony is a well-established phenomenon called a ‘caste system’, and has been thoroughly characterised within organisms with hierarchical communities, such as蚂蚁and蜜蜂。种姓形成也已被认可reef-shrimp，，，，sea anemonesand痣鼠。

然而,近年来有越来越多body of evidence showing that a complex caste system is present in a number ofDigenean trematodes（寄生虫）。

In a tightly organised society with a caste system, individuals are often divided into those that are reproductive and non-reproductive. Those that are non-reproductive (soldiers) are morphologically distinct from their reproductive counterparts and are specialised to defend the colony from invasion by attacking and killing invading organisms.

在Trematodes中，种姓制度在其生命周期的殖民阶段生效，当时它居住在水生蜗牛中。A奇迹从其确定的宿主沉积在水中的卵中孵化。然后，奇迹定位并感染其中间蜗牛宿主，如果成功，则建立了一段增殖的无性发育（一个菌落），从而产生了> 10,000个遗传上相同的幼虫。分配为士兵的幼虫trematodes（rediae）比其生殖同事更小，更薄，但口点相对较大，并且have been shown在可能发生其他trematodododos殖民地入侵的蜗牛宿主区域中，更活跃（并且部署不成比例地部署）。

研究2017and2020have both utilisedCerithideopsis加州to research the caste formation phenomena. The California horn snail is a marine gastropod recognised to play host to a diverse range of trematode species (at least 18), and so provided a perfect organism to research colony competition and the mechanisms behind soldier allocation.

站立税和最佳分配理论

The mechanism by which larval trematodes are allocated as either soldiers or reproductives is currently undetermined. However, it is known that resources are limited, and defences are costly. Much like the medieval kingdoms of Europe, trematodes pay a heavy cost to keep astanding army准备回应入侵。但是，他们为军队支付的费用不是像旧的封建主人那样的货币，而是以幼虫为士兵的分配而不是生殖产量减少的形式而不是其生殖形式。

Emlyn重置和她的同事理论上认为，将更多的殖民地分配为繁殖应优化菌落健身（即成功）在低入侵威胁水平下，但是当殖民地“暴露于较高的威胁水平时，应更加支持国防的威胁水平”。该理论被称为最佳分配理论，它预测，在具有士兵种姓的社会中，分配给士兵应该反映入侵的威胁水平。

Two hypotheses of optimal soldier allocation have been presented: inducible and constitutive mechanisms. Inducible (plastic) allocation infers that there will be different numbers of soldiers allocated to areas under a high threat of invasion (invasion fronts) in real time, whereas constitutive (innate) allocation essentially says that soldier allocation is fixed in a colony overtime, and that an increased threat of invasion in a specific area of the snail host doesn’t promote increased soldier allocation.

尽管有迹象蚂蚁，，，，黄蜂，甚至是trematodecan increase the numbers of soldiers in response to an increase in threat, we currently lack strong evidence if differences in the location of that threat can in some way influences soldier allocation.

Aplastic mechanism of soldier allocation when threat levels are high has indeed been shown insocial insects然而，一种trematode的物种，只有在以侵略性物种的侵略性弹性（也称为杂种侵略者）的侵略性弹性时，才显示在trematodes中。

因此，Emlyn的重置和同事试图在168个Trematode殖民地中量化入侵威胁和地点分配，用于六种trematode物种（每个蜗牛的一个菌落和trematode物种），跨越了一系列的入侵威胁，以降低质量分配机制的降低范围。。

Soldiers ready!

Results from the学习detail that soldier allocation substantially increased with an increased threat of invasion, and thus supporting a plastic mechanism of soldier allocation, and the optimal allocation theory. Interestingly, all six species of trematode shared a similar response, significantly increasing their solider allocation when the perceived threat level increased.

尽管士兵人数的增加和士兵分配可塑性的证据表明，但实际上，Trematode殖民地似乎并没有将大量士兵部署到高威胁入侵的阵线上。相反，他们选择简单地拥有一支更大的常规军以更好地捍卫自己的殖民地，这可能表明这些怪物会察觉到风险，甚至通过“记住”以前失败的入侵尝试。

竞争性饮食

Understandably, co-infection of the same snail host by multiple trematodes (colonies or species) creates opportunities for competition. For instance, it’s been shown that larvalechinostomes早于幼虫血块在他们共同的蜗牛宿主中，与血块物种的竞争和统治表现。Martina Laidemitt及其同事表明,证据表明echinostomes计谋ld reduce the prevalence of schistosomes implies they could be used as a biological control agent, and could provide an attractive approach to controlling血吸虫病。

如果您想了解有关这个有趣的话题的更多信息，请查看我们的other blog post关于Trematode士兵。