Biology Department, Mills College, 5000 MacArthur Blvd., Oakland, CA 94631, USA.
Biology Department, Mills College, 5000 MacArthur Blvd., Oakland, CA 94631, USA.
Int J Parasitol. 2021 Jun;51(7):587-598. doi: 10.1016/j.ijpara.2020.12.001. Epub 2021 Jan 26.
Understanding why some individuals are more prone to carry parasites and spread diseases than others is a key question in biology. Although epidemiologists and disease ecologists increasingly recognize that individuals of the same species can vary tremendously in their relative contributions to the emergence of diseases, very few empirical studies systematically assess consistent individual differences in parasite loads within populations over time. Two species of fleas (Oropsylla montana and Hoplopsyllus anomalous) and their hosts, California ground squirrels (Otospermophilus beecheyi), form a major complex for amplifying epizootic plague in the western United States. Understanding its biology is primarily of major ecological importance and is also relevant to public health. Here, we capitalize on a long-term data set to explain flea incidence on California ground squirrels at Briones Regional Park in Contra Costa County, USA. In a 7 year study, we detected 42,358 fleas from 2,759 live trapping events involving 803 unique squirrels from two free-living populations that differed in the amount of human disturbance in those areas. In general, fleas were most abundant and prevalent on adult males, on heavy squirrels, and at the pristine site, but flea distributions varied among years, with seasonal conditions (e.g., temperature, rainfall, humidity), temporally within summers, and between flea species. Although on-host abundances of the two flea species were positively correlated, each flea species occupied a distinctive ecological niche. The common flea (O. montana) occurred primarily on adults in cool, moist conditions in early summer whereas the rare flea (H. anomalous) was mainly on juveniles in hot, dry conditions in late summer. Beyond this, we uncovered significantly repeatable and persistent effects of host individual identity on flea loads, finding consistent individual differences among hosts in all parasite measures. Taken together, we reveal multiple determinants of parasites on free-living mammals, including the underappreciated potential for host heterogeneity - within populations - to structure the emergence of zoonotic diseases such as bubonic plague.
了解为什么有些人比其他人更容易携带寄生虫并传播疾病，是生物学中的一个关键问题。尽管流行病学家和疾病生态学家越来越认识到，同一物种的个体在对疾病出现的相对贡献方面可能存在巨大差异，但很少有实证研究系统地评估同一物种的个体寄生虫负荷在时间上的一致差异。两种跳蚤（Oropsylla montana 和 Hoplopsyllus anomalous）及其宿主加利福尼亚地松鼠（Otospermophilus beecheyi）在美国西部形成了一个主要的鼠疫放大复合体。了解其生物学主要具有重要的生态意义，也与公共卫生相关。在这里，我们利用一个长期数据集来解释美国加利福尼亚州康特拉科斯塔县布里恩斯地区公园的加利福尼亚地松鼠身上跳蚤的发病率。在一项为期 7 年的研究中，我们从涉及两个自由生活的种群的 803 只独特松鼠的 2759 次活捕事件中检测到 42358 只跳蚤，这两个种群在这些区域受到的人为干扰程度不同。一般来说，跳蚤在成年雄性、体重较重的松鼠和原始栖息地中最为丰富和普遍，但跳蚤的分布在不同年份有所不同，与季节性条件（如温度、降雨量、湿度）、夏季内的时间以及跳蚤物种有关。尽管两种跳蚤的宿主丰度呈正相关，但每种跳蚤都占据了独特的生态位。常见的跳蚤（O. montana）主要在初夏凉爽、潮湿的条件下寄生在成年松鼠身上，而稀有的跳蚤（H. anomalous）则主要在夏末炎热、干燥的条件下寄生在幼年松鼠身上。除此之外，我们还发现了宿主个体身份对跳蚤负荷的显著、持久影响，发现所有寄生虫指标在宿主中都存在一致的个体差异。总的来说，我们揭示了自由生活的哺乳动物身上寄生虫的多种决定因素，包括宿主异质性——在种群内——对鼠疫等人畜共患疾病出现的潜在影响，这一影响被低估了。
