Reisinger Lindsey S, Lodge David M
Ecology. 2016 Jun;97(6):1497-506. doi: 10.1890/15-1634.1.
Parasites can alter communities by reducing densities of keystone hosts, but few studies have examined how trait-mediated indirect effects of parasites can alter ecological communities. We test how trematode parasites (Microphallus spp.) that affect invasive crayfish (Orconectes rusticus) behavior alter how crayfish impact lake littoral communities. O. rusticus drive community composition in north temperate lakes, and predatory fish can reduce crayfish activity and feeding. In laboratory studies, Microphallus parasites also alter O. rusticus behavior: infected O. rusticus eat fewer macroinvertebrates and are bolder near predatory fish than uninfected individuals. We used a 2 x 2 factorial experiment to test how predatory fish and parasites affect O. rusticus impacts in large mesocosms over 4 weeks. We predicted (1) that when predators were absent, infected crayfish would have lower impacts than uninfected crayfish on macrophytes and macroinvertebrates (as well as reduced growth and higher mortality). However, (2) when predators were present but unable to consume crayfish, infected crayfish would have greater impacts (as well as greater growth and lower mortality) than uninfected crayfish because of increased boldness. Because of its effect on crayfish feeding behavior, we also predicted (3) that infection would alter macrophyte and macroinvertebrate community composition. In contrast to our first hypothesis, we found that infected and uninfected crayfish had similar impacts on lower trophic levels when predators were absent. Across all treatments, infected crayfish were more likely to be outside shelters and had greater growth than uninfected crayfish, suggesting that the reduced feeding observed in short-term experiments does not occur over longer timescales. However, in support of the second hypothesis, when predatory fish were present, infected crayfish ate more macroinvertebrates than did uninfected crayfish, likely due to increased boldness. We also observed a trend for greater macrophyte consumption associated with infection and a trend indicating infection might alter macroinvertebrate community composition. Our results suggest that parasites can alter aquatic communities in mesocosms merely by modifying host behavior.
寄生虫可通过降低关键宿主的密度来改变群落，但很少有研究探讨寄生虫的性状介导间接效应如何改变生态群落。我们测试了影响入侵小龙虾（铁锈色螯虾）行为的吸虫寄生虫（微茎属）如何改变小龙虾对湖泊沿岸群落的影响。铁锈色螯虾主导着北温带湖泊的群落组成，而掠食性鱼类会降低小龙虾的活动和摄食。在实验室研究中，微茎属寄生虫也会改变铁锈色螯虾的行为：受感染的铁锈色螯虾比未受感染的个体食用的大型无脊椎动物更少，并且在掠食性鱼类附近更大胆。我们进行了一项2×2析因实验，以测试掠食性鱼类和寄生虫如何在4周内影响大型中型生态缸中铁锈色螯虾的影响。我们预测：（1）当没有捕食者时，受感染的小龙虾对大型植物和大型无脊椎动物的影响将低于未受感染的小龙虾（以及生长减缓、死亡率升高）。然而，（2）当有捕食者但无法捕食小龙虾时，受感染的小龙虾由于更大胆，其影响（以及更大的生长和更低的死亡率）将大于未受感染的小龙虾。由于其对小龙虾摄食行为的影响，我们还预测（3）感染会改变大型植物和大型无脊椎动物的群落组成。与我们的第一个假设相反，我们发现当没有捕食者时，受感染和未受感染的小龙虾对较低营养级的影响相似。在所有处理中，受感染的小龙虾比未受感染的小龙虾更有可能在庇护所外，并且生长更快，这表明在短期实验中观察到的摄食减少在更长的时间尺度上不会发生。然而，支持第二个假设的是，当有掠食性鱼类时，受感染的小龙虾比未受感染的小龙虾食用更多的大型无脊椎动物，这可能是由于更大胆。我们还观察到与感染相关的大型植物消耗增加的趋势，以及表明感染可能改变大型无脊椎动物群落组成的趋势。我们的结果表明，寄生虫仅通过改变宿主行为就可以改变中型生态缸中的水生群落。
