Wood Chelsea L, Byers James E, Cottingham Kathryn L, Altman Irit, Donahue Megan J, Blakeslee April M H
Department of Biological Sciences, Dartmouth College, 103 Gilman Hall, Hanover, NH 03755, USA.
Proc Natl Acad Sci U S A. 2007 May 29;104(22):9335-9. doi: 10.1073/pnas.0700062104. Epub 2007 May 18.
Parasites often play an important role in modifying the physiology and behavior of their hosts and may, consequently, mediate the influence hosts have on other components of an ecological community. Along the northern Atlantic coast of North America, the dominant herbivorous snail Littorina littorea structures rocky intertidal communities through strong grazing pressure and is frequently parasitized by the digenean trematode Cryptocotyle lingua. We hypothesized that the effects of parasitism on host physiology would induce behavioral changes in L. littorea, which in turn would modulate L. littorea's influence on intertidal community composition. Specifically, we hypothesized that C. lingua infection would alter the grazing rate of L. littorea and, consequently, macroalgal communities would develop differently in the presence of infected versus uninfected snails. Our results show that uninfected snails consumed 40% more ephemeral macroalgal biomass than infected snails in the laboratory, probably because the digestive system of infected snails is compromised by C. lingua infection. In the field, this weaker grazing by infected snails resulted in significantly greater expansion of ephemeral macroalgal cover relative to grazing by uninfected snails. By decreasing the per-capita grazing rate of the dominant herbivore, C. lingua indirectly affects the composition of the macroalgal community and may in turn affect other species that depend on macroalgae for resources or habitat structure. In light of the abundance of parasites across systems, we suggest that, through trait-mediated indirect effects, parasites may be a common determinant of structure in ecological communities.
寄生虫通常在改变宿主的生理和行为方面发挥重要作用，因此可能会介导宿主对生态群落其他组成部分的影响。在北美北大西洋沿岸，占主导地位的草食性蜗牛滨螺通过强大的啃食压力构建潮间带岩石群落，并且经常被复殖吸虫隐孔吸虫寄生。我们假设，寄生虫对宿主生理的影响会导致滨螺的行为发生变化，进而调节滨螺对潮间带群落组成的影响。具体而言，我们假设隐孔吸虫感染会改变滨螺的啃食率，因此，在有感染螺和未感染螺的情况下，大型藻类群落的发展会有所不同。我们的结果表明，在实验室中，未感染的蜗牛消耗的临时性大型藻类生物量比感染的蜗牛多40%，这可能是因为感染蜗牛的消化系统受到隐孔吸虫感染的影响。在野外，与未感染蜗牛的啃食相比，感染蜗牛较弱的啃食导致临时性大型藻类覆盖面积显著扩大。通过降低优势草食动物的人均啃食率，隐孔吸虫间接影响大型藻类群落的组成，进而可能影响其他依赖大型藻类获取资源或栖息地结构的物种。鉴于整个生态系统中寄生虫数量众多，我们认为，通过性状介导的间接影响，寄生虫可能是生态群落结构的一个常见决定因素。
