Data from: Survival of the feces: does a nematode lungworm adaptively manipulate the behavior of its cane toad host?

Parasites can enhance their fitness by modifying the behavior of their hosts in ways that increase rates of production and transmission of parasite larvae. We used an antihelminthic drug to experimentally alter infections of lungworms (Rhabdias pseudosphaerocephala) in cane toads (Rhinella marina). We then compared subsequent behaviors of dewormed toads versus toads that retained infections. Both in the laboratory and in the field, the presence of parasites induced hosts to select higher body temperatures (thereby increasing rates of lungworm egg production), to defecate in moister sites, and to produce feces with higher moisture content (thereby enhancing survival of larvae shed in feces). Because those behavioral modifications enhance rather than decrease parasite fitness, they are likely to have arisen as adaptive manipulations of host behavior rather than as host adaptations to combat infection or as nonadaptive consequences of infection on host physiology. However, the mechanisms by which lungworms alter cane toad thermal preference and defecation are not known. Although many examples of host manipulation by parasites involve intermediate hosts facilitating their own demise, our findings indicate that manipulation of definitive hosts can be as subtle as when and where to defecate.

寄生虫可通过调控宿主行为，提升自身幼虫的产出与传播效率，进而增强自身适合度。本研究通过抗蠕虫药（antihelminthic drug）对甘蔗蟾蜍（Rhinella marina）体内的肺线虫（Rhabdias pseudosphaerocephala）感染状态进行实验性调控，随后对比了驱虫后蟾蜍与仍保留感染状态蟾蜍的后续行为差异。
无论是在实验室环境还是野外生境中，寄生虫感染均会促使宿主选择更高的体温（以此提升肺线虫虫卵的产出速率）、在湿度更高的场所排便，且排出粪便的含水量更高（进而提升随粪便排出的幼虫存活率）。由于此类行为改变反而提升了而非降低了寄生虫的适合度，因此这些现象更可能是寄生虫对宿主行为的适应性操控，而非宿主对抗感染的适应性演化结果，亦非感染对宿主生理产生的非适应性副作用。不过，肺线虫调控甘蔗蟾蜍体温偏好与排便行为的具体机制仍未明确。尽管已报道的诸多寄生虫操控宿主行为的案例多涉及中间宿主促成自身消亡，但本研究结果表明，对终末宿主的操控也可以极为细微，仅涉及排便的时机与场所。