Zoology, School of Environmental and Rural Science, University of New England, NSW 2351, Australia.
Int J Parasitol. 2011 Aug 15;41(10):1063-8. doi: 10.1016/j.ijpara.2011.05.001. Epub 2011 May 31.
Animals living in colonies or collectives composed of highly-related individuals often produce morphs that are physically and behaviourally specialised to perform specific tasks. Because such morphs are often sterile, their production represents a fitness cost for the colony and there should be an optimal ratio of the numbers of sterile specialists and reproductive members that may be adjustable to environmental conditions. Trematode parasites undergo asexual multiplication within their snail intermediate host, resulting in large numbers of clonal stages known as rediae or sporocysts, depending on the trematode species. In areas with high prevalences of infection, the host can be infected by multiple species, which can lead to intense competition for limited resources. Here, we describe the existence of specialised 'mini-rediae' in the trematode Philophthalmus sp. that are morphologically and functionally specialised for interspecific competition. Mini-rediae were observed feeding on the sporocysts of a co-occurring trematode species -Maritrema novaezealandensis. In addition, in larger snails - which are less likely to have M. novaezealandensis infections -Philophthalmus sp. produces relatively fewer mini-rediae than expected. Our findings support results from a prior study which demonstrated the existence of morphs that perform specialised functions in antagonistic interspecific interactions in trematodes, and additionally shows that the number of these morphs in each host is associated with the likelihood of encountering other species within the same host. Trematodes may thus provide interesting models for studying morphological specialisation in colonial organisms.
生活在高度相关个体组成的群体或集体中的动物通常会产生形态上和行为上专门化的变体，以执行特定任务。由于这些变体通常是不育的，因此它们的产生对群体来说是一种适应度成本，而且不育专家和生殖成员的数量应该存在一个最优比例，可以根据环境条件进行调整。吸虫寄生虫在其蜗牛中间宿主内进行无性繁殖，导致大量无性繁殖阶段，称为雷迪氏（rediae）或孢子囊（sporocysts），具体取决于吸虫的种类。在感染率较高的地区，宿主可能会被多种寄生虫感染，这可能导致对有限资源的激烈竞争。在这里，我们描述了 Philophthalmus sp. 吸虫中专门的“迷你雷迪氏”的存在，它们在形态和功能上专门用于种间竞争。观察到迷你雷迪氏在共生吸虫 Maritrema novaezealandensis 的孢子囊中取食。此外，在较大的蜗牛中——它们不太可能感染 M. novaezealandensis——Philophthalmus sp. 产生的迷你雷迪氏数量相对较少，这低于预期。我们的发现支持了先前一项研究的结果，该研究表明在吸虫中存在在种间对抗性相互作用中执行专门功能的形态，并且还表明，每个宿主中这些形态的数量与在同一宿主中遇到其他物种的可能性有关。因此，吸虫可能为研究群体生物中的形态特化提供了有趣的模型。
