Eads David A, Hoogland John L
Department of Biology, Colorado State University, Fort Collins, Colorado 80523. Correspondence should be sent to David A. Eads at:
J Parasitol. 2017 Aug;103(4):309-319. doi: 10.1645/16-195. Epub 2017 Mar 30.
Fleas (Insecta: Siphonaptera) are hematophagous ectoparasites that can reduce the fitness of vertebrate hosts. Laboratory populations of fleas decline under dry conditions, implying that populations of fleas will also decline when precipitation is scarce under natural conditions. If precipitation and hence vegetative production are reduced, however, then herbivorous hosts might suffer declines in body condition and have weakened defenses against fleas, so that fleas will increase in abundance. We tested these competing hypotheses using information from 23 yr of research on 3 species of colonial prairie dogs in the western United States: Gunnison's prairie dog (Cynomys gunnisoni, 1989-1994), Utah prairie dog (Cynomys parvidens, 1996-2005), and white-tailed prairie dog (Cynomys leucurus, 2006-2012). For all 3 species, flea-counts per individual varied inversely with the number of days in the prior growing season with >10 mm of precipitation, an index of the number of precipitation events that might have caused a substantial, prolonged increase in soil moisture and vegetative production. Flea-counts per Utah prairie dog also varied inversely with cumulative precipitation of the prior growing season. Furthermore, flea-counts per Gunnison's and white-tailed prairie dog varied inversely with cumulative precipitation of the just-completed January and February. These results complement research on black-tailed prairie dog (Cynomys ludovicianus) and might have important ramifications for plague, a bacterial disease transmitted by fleas that devastates populations of prairie dogs. In particular, our results might help to explain why, at some colonies, epizootics of plague, which can kill >95% of prairie dogs, are more likely to occur during or shortly after periods of reduced precipitation. Climate change is projected to increase the frequency of droughts in the grasslands of western North America. If so, then climate change might affect the occurrence of plague epizootics among prairie dogs and other mammalian species that associate with them.
跳蚤（昆虫纲：蚤目）是吸血性体外寄生虫，会降低脊椎动物宿主的健康状况。实验室中的跳蚤种群在干燥条件下会减少，这意味着在自然条件下降雨稀少时，跳蚤种群也会减少。然而，如果降水量减少，进而植物产量降低，那么食草宿主的身体状况可能会下降，对跳蚤的抵抗力也会减弱，从而导致跳蚤数量增加。我们利用对美国西部3种群居草原犬鼠进行的23年研究所得信息，对这些相互矛盾的假设进行了检验：甘尼森草原犬鼠（Cynomys gunnisoni，1989 - 1994年）、犹他草原犬鼠（Cynomys parvidens，1996 - 2005年）和白尾草原犬鼠（Cynomys leucurus，2006 - 2012年）。对于所有这3个物种，每只动物身上的跳蚤数量与前一个生长季节降水量超过10毫米的天数呈负相关，该天数是可能导致土壤湿度和植物产量大幅、持续增加的降水事件数量的一个指标。每只犹他草原犬鼠身上的跳蚤数量也与前一个生长季节的累计降水量呈负相关。此外，每只甘尼森草原犬鼠和白尾草原犬鼠身上的跳蚤数量与刚刚结束的1月和2月的累计降水量呈负相关。这些结果补充了对黑尾草原犬鼠（Cynomys ludovicianus）的研究，并且可能对鼠疫有重要影响，鼠疫是一种由跳蚤传播的细菌性疾病，会使草原犬鼠种群遭受重创。特别是，我们的结果可能有助于解释为什么在一些群落中，能杀死95%以上草原犬鼠的鼠疫 epizootics 在降水量减少期间或之后不久更有可能发生。预计气候变化会增加北美西部草原干旱的频率。如果是这样，那么气候变化可能会影响草原犬鼠及与其相关的其他哺乳动物物种中鼠疫 epizootics 的发生情况。
