Vance Sarah A, Peckarsky Barbara L
Department of Entomology, Cornell University, Comstock Hall, Ithaca, NY 14853, USA, , , , , , US.
Oecologia. 1997 Mar;110(1):147-152. doi: 10.1007/s004420050143.
We investigated how infection by the mermithid nematode Gasteromermis sp. affected predation on its nymphal mayfly host, Baetisbicaudatus, by two invertebrate predators - the stonefly nymphs of Kogotusmodestus and the caddisfly larvae of Rhyacophilahyalinata. Predation trials and behavioral observations were conducted in stream-side, flow-through experimental chambers. When parasitized and unparasitized prey were offered in equal numbers, K. modestus consumed significantly more parasitized than unparasitized nymphs. R. hyalinata consumed equal numbers of both prey types. Behavioral observations of foraging K.␣modestus on parasitized and unparasitized prey suggested that the increased consumption of parasitized nymphs was due to differences in the behavior of infected mayflies in response to the predator. Specifically, parasitized nymphs drifted less often to escape an approaching predator (non-contact encounters) compared to unparasitized nymphs, which increased the number of contact encounters and attacks that occurred between K.␣modestus and parasitized prey. Because all hosts are castrated, these behavioral alterations affect only the fitness of the parasite, which is killed along with its host by invertebrate predation. We present a number of hypotheses to explain why the parasite causes increased predation on its host. These include the large size of the parasite affecting the sensory abilities of the host, the larger energetic costs of escape behavior for parasitized individuals, and natural selection from fish predation against drifting behavior by parasitized individuals.
我们研究了索线虫纲线虫Gasteromermis sp.的感染如何影响其蜉蝣宿主双尾蚋（Baetis bicaudatus）被两种无脊椎动物捕食者——谦逊石蝇若虫（Kogotus modestus）和透明长角石蛾幼虫（Rhyacophila hyalinata）捕食的情况。捕食试验和行为观察在溪边的流通实验室内进行。当提供数量相等的被寄生和未被寄生的猎物时，谦逊石蝇若虫捕食的被寄生若虫显著多于未被寄生的若虫。透明长角石蛾幼虫捕食的两种猎物数量相等。对谦逊石蝇若虫捕食被寄生和未被寄生猎物的行为观察表明，被寄生若虫被捕食量增加是由于受感染的蜉蝣对捕食者的行为差异所致。具体而言，与未被寄生的若虫相比，被寄生的若虫为躲避接近的捕食者（非接触性相遇）而漂移的频率更低，这增加了谦逊石蝇若虫与被寄生猎物之间的接触性相遇和攻击次数。由于所有宿主都会被阉割，这些行为改变仅影响寄生虫的适合度，而寄生虫会与其宿主一起被无脊椎动物捕食者杀死。我们提出了一些假说来解释寄生虫为何会导致其宿主被捕食增加。这些假说包括寄生虫的体型大小影响宿主的感官能力、被寄生个体逃避行为的能量成本更高，以及鱼类捕食对被寄生个体漂移行为的自然选择。
