Thieltges David W, Ferguson MacNeill A D, Jones Cathy S, Krakau Manuela, de Montaudouin Xavier, Noble Leslie R, Reise Karsten, Poulin Robert
Department of Zoology, University of Otago, Dunedin, New Zealand.
Oecologia. 2009 May;160(1):163-73. doi: 10.1007/s00442-009-1276-2. Epub 2009 Feb 3.
The similarity in species composition between two communities generally decays as a function of increasing distance between them. Parasite communities in vertebrate definitive hosts follow this pattern but the respective relationship in intermediate invertebrate hosts of parasites with complex life cycles is unknown. In intermediate hosts, parasite communities are affected not only by the varying vagility of their definitive hosts (dispersing infective propagules) but also by the necessary coincidence of all their hosts in environmentally suitable localities. As intermediate hosts often hardly move they do not contribute to parasite dispersal. Hence, their parasite assemblages may decrease faster in similarity with increasing distance than those in highly mobile vertebrate definitive hosts. We use published field survey data to investigate distance decay of similarity in trematode communities from three prominent coastal molluscs of the Eastern North-Atlantic: the gastropods Littorina littorea and Hydrobia ulvae, and the bivalve Cerastoderma edule. We found that the similarity of trematode communities in all three hosts decayed with distance, independently of local sampling effort, and whether or not the parasites used the mollusc as first or second intermediate host in their life cycle. In H. ulvae, the halving distance (i.e. the distance that halves the similarity from its initial similarity at 1 km distance) for the trematode species using birds as definitive hosts was approximately two to three times larger than for species using fish. The initial similarities (estimated at 1 km distance) among trematode communities were relatively higher, whereas mean halving distances were lower, compared to published values for parasite communities in vertebrate hosts. We conclude that the vagility of definitive hosts accounts for a high similarity at the local scale, while the strong decay of similarity across regions is a consequence of the low probability that all necessary hosts and suitable environmental conditions coincide on a large scale.
两个群落之间物种组成的相似性通常会随着它们之间距离的增加而衰减。脊椎动物终末宿主中的寄生虫群落遵循这一模式，但对于具有复杂生命周期的寄生虫，其在中间无脊椎动物宿主中的相应关系尚不清楚。在中间宿主中，寄生虫群落不仅受到其终末宿主不同移动性（传播感染性繁殖体）的影响，还受到所有宿主在环境适宜地点的必要重合的影响。由于中间宿主通常很少移动，它们对寄生虫传播没有贡献。因此，与高度移动的脊椎动物终末宿主相比，它们的寄生虫组合相似性可能会随着距离增加而更快地降低。我们使用已发表的实地调查数据，研究了来自北大西洋东部三种主要沿海软体动物的吸虫群落相似性的距离衰减情况：腹足纲的滨螺和浒苔，以及双壳纲的欧洲鸟蛤。我们发现，所有三种宿主中吸虫群落的相似性都随着距离而衰减，与当地采样努力无关，也与寄生虫在其生命周期中是否将软体动物用作第一或第二中间宿主无关。在浒苔中，以鸟类为终末宿主的吸虫物种的减半距离（即距离，该距离使相似度从1公里距离处的初始相似度减半）大约是那些以鱼类为终末宿主的物种的两到三倍。与脊椎动物宿主中寄生虫群落的已发表值相比，吸虫群落之间的初始相似度（估计在1公里距离处）相对较高，而平均减半距离较低。我们得出结论，终末宿主的移动性在局部尺度上导致了高度相似性，而跨区域相似性的强烈衰减是所有必要宿主和适宜环境条件在大尺度上重合概率较低的结果。
