Data from: Little impact of over-winter parasitism on a free-ranging ungulate in the high Arctic

1.Macroparasites have a central place in wildlife ecology because they have the potential to regulate host populations through effects on reproduction and/or survival. However, there remains a paucity of studies that have demonstrated the regulatory role of these parasites in free-ranging animals.

2.Previous work on Svalbard reindeer demonstrated that the experimental removal of the parasitic gastrointestinal nematode Ostertagia gruehneri transmitted in summer, improved reindeer fecundity, and that the species was capable of mediating a density-dependent reduction in fecundity.

3.The main coexisting parasitic nematode in the system, Marshallagia marshalli, exhibits a contrasting life-history with low abundances in summer and an increase during the winter. Here, we examine the impact of this over-winter infection on fitness of female reindeer in the same population.

4.Worm burdens were removed at the start of the winter in October using a novel delayed-release anthelmintic bolus. Body mass and pregnancy rates were recorded for animals recaptured five (February) and seven (April) months later. The sub-set of treated animals recaptured in February was treated again with anthelmintic to remove newly acquired nematodes. The experiment was replicated over six winters (2006/7-2011/12) with a total of 343 recaptures, comprising 145 individual animals.

5.We found little effect of anthelmintic treatment on reindeer body mass or pregnancy rates during the winter, suggesting that nematode infection during this time does not significantly affect fitness of Svalbard reindeer.

6.Our studies are consistent with marked virulence nutritional trade-offs in this system and highlights the need to integrate studies of parasite co-infection, inter-specific competition and community ecology to understand parasite impacts on hosts.

1. 大型寄生虫（Macroparasites）在野生动物生态学中占据核心地位，因为它们可通过影响宿主的繁殖和/或存活来调控宿主种群。然而，目前仍鲜有研究证实这类寄生虫在野外自由活动的动物中存在调控作用。
2. 此前针对斯瓦尔巴德驯鹿（Svalbard reindeer）的研究表明，实验移除夏季传播的寄生性胃肠道线虫（parasitic gastrointestinal nematode）奥斯特线虫（Ostertagia gruehneri）可提升驯鹿的繁殖力，且该线虫能够介导繁殖力的密度依赖性下降。
3. 该系统中的主要共寄生线虫为马歇尔线虫（Marshallagia marshalli），其生活史与奥斯特线虫形成鲜明对比：夏季丰度较低，冬季则逐渐升高。本研究旨在探究这种越冬感染对同一种群中雌性驯鹿适合度的影响。
4. 研究人员于十月初冬通过投喂新型缓释驱虫丸（delayed-release anthelmintic bolus）清除宿主的寄生虫负荷。分别在五个月后（二月）和七个月后（四月）对再次捕获的个体记录其体质量与妊娠率。对于二月重捕的经处理组个体，再次投喂驱虫药以清除其新感染的线虫。本实验于2006/7至2011/12六个冬季间重复开展，总计完成343次重捕，涉及145头个体。
5. 研究发现，驱虫处理对驯鹿冬季的体质量与妊娠率几乎无影响，这表明该时段的线虫感染并未显著影响斯瓦尔巴德驯鹿的适合度。
6. 本研究结果与该系统中显著的毒力-营养权衡现象相符，同时强调需整合寄生虫共感染、种间竞争与群落生态学的相关研究，以阐明寄生虫对宿主的影响机制。