Data from: Ectoparasites and fitness of female Columbian ground squirrels

Parasites play an important role in the evolution of host traits via natural selection, coevolution and sexually selected ornaments used in mate choice. These evolutionary scenarios assume fitness costs for hosts. To test this assumption, we conducted an ectoparasite removal experiment in free-living Columbian ground squirrels (Urocittelus columbianus) in four populations over three years. Adult females were randomly chosen to be either experimentally treated with anti-parasite treatments (spot-on solution and flea powder, N = 61) or a sham treatment (control, N = 44). We expected that experimental females would show better body condition, increased reproductive success and enhanced survival. Contrary to our expectations, body mass was not significantly different between treatments at mating, birth of litter or weaning of young. Further, neither number nor size of young at weaning differed significantly between the two treatments. Survival to the next spring for adult females and juveniles was not significantly different between experimental and control treatments. Finally, annual fitness was not affected by the treatments. We concluded that females and their offspring were able compensate for the presence of ectoparasites, suggesting little or no fitness costs of parasites for females in the different colonies and during the years of our experiments.寄生虫可通过自然选择、协同进化以及配偶选择中所使用的性选择装饰物，在宿主性状演化过程中发挥关键作用。此类演化场景均假设宿主需付出适合度代价。为验证这一假设，我们历时三年，在四个种群的自由生活哥伦比亚黄鼠（*Urocittelus columbianus*）中开展了体外寄生虫（ectoparasite）移除实验。我们将成年雌性个体随机分为两组：实验组接受抗寄生虫处理（背滴型药剂与蚤粉，样本量N=61），对照组接受假处理（样本量N=44）。我们最初预期实验组雌性的体况更优、繁殖成功率更高且存活率更强。但与预期相悖的是，在交配期、产仔期与幼崽断奶期，两组个体的体重均无显著差异。此外，断奶幼崽的数量与体型在两组间亦无显著区别。成年雌性与幼崽来年春季的存活率，在实验组与对照组间同样无显著差异。最终，年度适合度并未受到处理的影响。我们由此得出结论：雌性黄鼠及其后代能够补偿体外寄生虫带来的影响，表明在本实验涉及的不同种群与实验年份中，寄生虫并未给雌性个体带来显著的适合度代价，或仅存在极微的适合度代价。