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率与传播速率，进而增强自身的适合度（fitness）。本研究借助抗蠕虫药（antihelminthic drug），对蔗蟾（Rhinella marina）体内的肺线虫（Rhabdias pseudosphaerocephala）感染状态开展实验性干预，随后对比了驱虫后蔗蟾与保留感染状态蔗蟾的后续行为差异。无论是实验室环境还是野外生境，寄生虫感染均会诱导宿主选择更高体温——该行为可提升肺线虫虫卵产出率——同时使宿主偏好高湿度场所排便，并排出含水量更高的粪便，进而提升随粪便排出的幼虫存活率。鉴于此类行为修饰非但未降低反而提升了寄生虫的适合度，因此它们更可能是寄生虫对宿主行为的适应性操控策略，而非宿主对抗感染的适应性演化特征，亦非感染对宿主生理造成的非适应性后果。不过，肺线虫调控蔗蟾体温偏好与排便行为的具体机制目前尚不明确。尽管诸多已报道的寄生虫操控宿主案例均涉及中间宿主被诱导死亡，本研究结果却表明，对终末宿主（definitive host）的操控可以十分微妙，仅体现在排便的时机与场所选择上。