Department of Biology, University of Oulu, Oulu, Finland.
Oecologia. 2011 Aug;166(4):985-95. doi: 10.1007/s00442-011-1951-y. Epub 2011 Mar 9.
Invasive generalist ectoparasites provide a tool to study factors affecting expansion rates. An increase in the number of host species may facilitate geographic range expansion by increasing the number of suitable habitats and by affecting local extinction and colonization rates. A geographic perspective on parasite host specificity and its implications on range expansion are, however, insufficiently understood. We conducted a field study to explore if divergent host specificity could explain the observed variation in expansion rates between Fennoscandian populations of the deer ked (Lipoptena cervi), which is a blood-feeding ectoparasitic fly of cervids. We found that the rapidly expanding eastern population in Finland appears to specialize on moose, whereas the slowly expanding western population in Norway breeds successfully on both moose and roe deer. The eastern population was also found to utilize the wild forest reindeer as an auxiliary host, but this species is apparently of low value for L. cervi in terms of adult maintenance, reproductive output and offspring quality. Abundant numbers of roe deer and white-tailed deer were observed to be apparently uninfected in Finland, suggesting that host use is not a plastic response to host availability, but rather a consequence of population-level evolutionary changes. Locally compatible hosts were found to be the ones sharing a long history with the deer ked in the area. Cervids that sustained adult deer keds also allowed successful reproduction. Thus, host use is probably determined by the ability of the adult to exploit particular host species. We conclude that a wide host range alone does not account for the high expansion rate or wide geographic distribution of the deer ked, although loose ecological requirements would increase habitat availability.
入侵性的泛化外寄生虫为研究影响扩张率的因素提供了工具。宿主物种数量的增加可能通过增加适宜栖息地的数量，并通过影响当地的灭绝和定植率，促进地理范围的扩张。然而，寄生虫宿主特异性的地理视角及其对范围扩张的影响还没有得到充分的理解。我们进行了一项实地研究，以探讨趋异的宿主特异性是否可以解释在芬诺斯堪的纳维亚地区的鹿虻种群（Lipoptena cervi）中观察到的扩张率的变化，鹿虻是一种吸血的外寄生虫蝇，以鹿科动物为食。我们发现，在芬兰迅速扩张的东部种群似乎专门以驼鹿为食，而在挪威缓慢扩张的西部种群在驼鹿和狍子上都能成功繁殖。东部种群也被发现将野生森林驯鹿作为辅助宿主，但就鹿虻而言，这种物种在成虫维持、生殖输出和后代质量方面的价值显然较低。在芬兰，大量的狍子和白尾鹿显然没有被感染，这表明宿主的利用不是对宿主可用性的可塑性反应，而是种群水平进化变化的结果。在该地区与鹿虻有长期历史的本地相容宿主被发现。维持成虫鹿虻的鹿科动物也允许成功繁殖。因此，宿主的利用可能取决于成虫利用特定宿主物种的能力。我们的结论是，广泛的宿主范围本身并不能解释鹿虻的高扩张率或广泛的地理分布，尽管松散的生态要求会增加栖息地的可用性。
