Department of Biology, University of Oulu, PO Box 3000, FI-90014 Oulu, Finland.
Parasitology. 2012 Jun;139(7):926-33. doi: 10.1017/S0031182012000091. Epub 2012 Feb 8.
Off-host stages of temperate parasites must cope with low temperatures. Cold tolerance is often highest in winter, as a result of diapause and cold acclimation, and low during the active summer stages. In some blood-feeding ectoparasites, offspring provisioning determines cold tolerance through all the non-feeding, off-host stages. Large size increases survival in the cold, but so far seasonal variation in within-female offspring size has not been associated with offspring cold tolerance. The deer ked (Lipoptena cervi) reproduces on cervids from autumn to spring. Newborn pupae drop off the host, facing frosts without any acclimation. We examined cold tolerance through 4 seasons and from birth to adulthood by means of short- and long-term frost exposure. We expected females to produce more tolerant offspring in winter than in spring. Large spring pupae survived prolonged frosts better than did small winter pupae. Thus more tolerant offspring were not produced when the temperature outside the host is at its lowest. Unexpectedly, the freezing points were -20 °C or below all year round. We showed that high cold tolerance is possible without acclimation regardless of life stage, which presumably correlates with other survival characteristics, such as the starvation resistance of free-living ectoparasites.
兼性寄生虫的非宿主阶段必须应对低温。由于休眠和低温驯化，冬季的耐寒性通常最高，而在活跃的夏季阶段则较低。在一些吸血外寄生虫中，后代的营养供应通过所有非摄食、非宿主阶段决定了对寒冷的耐受性。较大的体型增加了在寒冷中的存活率，但到目前为止，雌性个体内部后代大小的季节性变化与后代的耐寒性无关。鹿虱（Lipoptena cervi）从秋季到春季在鹿类动物上繁殖。新出生的蛹从宿主身上脱落，在没有任何驯化的情况下遭遇霜冻。我们通过短期和长期的霜暴露，在 4 个季节以及从出生到成年的过程中检查了耐寒性。我们预计雌性在冬季比春季会产生更能耐受寒冷的后代。较大的春季蛹比小的冬季蛹更能在长时间的霜冻中存活下来。因此，当宿主外的温度处于最低水平时，并没有产生更耐受寒冷的后代。出乎意料的是，全年的冰点都在-20°C 或以下。我们表明，无论生命阶段如何，无需驯化即可实现高耐寒性，这可能与其他生存特征相关，如自由生活的外寄生虫的抗饥饿能力。
