Bertolino Sandro, Wauters Luc A, De Bruyn Luc, Canestri-Trotti Giorgio
Laboratory of Entomology and Zoology, DIVAPRA, University of Turin, Via L da Vinci 44, 10095 Grugliasco (TO), Italy.
Oecologia. 2003 Oct;137(2):286-95. doi: 10.1007/s00442-003-1345-x. Epub 2003 Jul 24.
We investigated the relative importance of environmental factors versus host phenotype in determining parasite prevalence in Eurasian red squirrels (Sciurus vulgaris). One hundred and forty-three fecal samples of 116 different squirrels collected in 2000 and 2001 from five study areas in the Italian Alps, were examined for intestinal protozoans. Two species of Eimeria were present with a medium to high prevalence in both years and in all areas, while two other species were rare, occurring only in some areas and not in all years. Cryptosporidium parvum had a high prevalence in the two study areas of the Western Alps, while in the three areas of the Central Alps it was recorded only once. The prevalence of Eimeria sciurorum and C. parvum fluctuated in parallel with squirrel density, suggesting a possible correlation between the presence of these protozoans and host density. A gender effect on E. sciurorum prevalence at low density could be explained by different space use patterns and social organization of males and females. C. parvum occurred more frequently in young squirrels, suggesting an acquired immunity in adults, but age-related susceptibility was not found for eimerian species. The coccidian community was more similar within than between regions, and study area and year were key parameters in predicting coccidia infection. There was no evidence of competition between coccidian species, but one positive interaction between E. sciurorum and E. andrewsi was observed. Our results suggest that the effects of geographic region, area features, and year effects probably related to fluctuations in host population density, were more important than individual phenotypic host characteristics in structuring the coccidian assemblage and determining levels of parasite prevalence in red squirrel populations.
我们研究了环境因素与宿主表型在决定欧亚红松鼠（Sciurus vulgaris）寄生虫感染率方面的相对重要性。2000年和2001年从意大利阿尔卑斯山的五个研究区域收集了116只不同松鼠的143份粪便样本，检测其中的肠道原生动物。艾美耳球虫的两个物种在这两年以及所有区域的感染率都处于中高水平，而另外两个物种则很罕见，仅在某些区域出现且并非每年都有。微小隐孢子虫在西阿尔卑斯山的两个研究区域感染率很高，而在中阿尔卑斯山的三个区域仅记录到一次。松鼠艾美耳球虫和微小隐孢子虫的感染率与松鼠密度平行波动，表明这些原生动物的存在与宿主密度之间可能存在关联。低密度时雄性和雌性在空间利用模式和社会组织上的差异可以解释对松鼠艾美耳球虫感染率的性别影响。微小隐孢子虫在幼龄松鼠中更常见，表明成年松鼠具有获得性免疫力，但未发现艾美耳球虫物种存在与年龄相关的易感性。球虫群落内部比不同区域之间更为相似，研究区域和年份是预测球虫感染的关键参数。没有证据表明球虫物种之间存在竞争，但观察到松鼠艾美耳球虫和安德鲁氏艾美耳球虫之间存在一种正向相互作用。我们的结果表明，地理区域、区域特征以及可能与宿主种群密度波动相关的年份效应，在构建球虫组合和决定红松鼠种群寄生虫感染率水平方面，比宿主个体表型特征更为重要。
