Gangoso Laura, Grande Juan M, Lemus Jesús A, Blanco Guillermo, Grande Javier, Donázar José A
Department of Conservation Biology, Estación Biológica de Doñana (CSIC), Sevilla, Spain.
PLoS One. 2009 Jul 22;4(7):e6333. doi: 10.1371/journal.pone.0006333.
A generalized decline in populations of Old World avian scavengers is occurring on a global scale. The main cause of the observed crisis in continental populations of these birds should be looked for in the interaction between two factors -- changes in livestock management, including the increased use of pharmaceutical products, and disease. Insular vertebrates seem to be especially susceptible to diseases induced by the arrival of exotic pathogens, a process often favored by human activities, and sedentary and highly dense insular scavengers populations may be thus especially exposed to infection by such pathogens. Here, we compare pathogen prevalence and immune response in insular and continental populations of the globally endangered Egyptian vulture under similar livestock management scenarios, but with different ecological and evolutionary perspectives.
METHODS/PRINCIPAL FINDINGS: Adult, immature, and fledgling vultures from the Canary Islands and the Iberian Peninsula were sampled to determine a) the prevalence of seven pathogen taxa and b) their immunocompetence, as measured by monitoring techniques (white blood cells counts and immunoglobulins). In the Canarian population, pathogen prevalence was higher and, in addition, an association among pathogens was apparent, contrary to the situation detected in continental populations. Despite that, insular fledglings showed lower leukocyte profiles than continental birds and Canarian fledglings infected by Chlamydophila psittaci showed poorer cellular immune response.
CONCLUSIONS/SIGNIFICANCE: A combination of environmental and ecological factors may contribute to explain the high susceptibility to infection found in insular vultures. The scenario described here may be similar in other insular systems where populations of carrion-eaters are in strong decline and are seriously threatened. Higher susceptibility to infection may be a further factor contributing decisively to the extinction of island scavengers in the present context of global change and increasing numbers of emerging infectious diseases.
全球范围内，旧大陆食腐鸟类的数量普遍在减少。这些鸟类在大陆种群中所观察到的危机，其主要原因应从两个因素的相互作用中去寻找——畜牧管理的变化，包括医药产品使用的增加，以及疾病。岛屿脊椎动物似乎对由外来病原体的到来所引发的疾病格外易感，这一过程往往因人类活动而加剧，因此，定居且高密度的岛屿食腐动物种群可能尤其容易受到此类病原体的感染。在此，我们比较了在相似畜牧管理情景下，但具有不同生态和进化视角的全球濒危埃及秃鹫的岛屿种群和大陆种群中的病原体流行率及免疫反应。
方法/主要发现：对来自加那利群岛和伊比利亚半岛的成年、未成年及雏鸟进行采样，以确定：a）七种病原体类群的流行率；b）通过监测技术（白细胞计数和免疫球蛋白）所测定的它们的免疫能力。在加那利群岛的种群中，病原体流行率更高，此外，病原体之间存在明显的关联，这与在大陆种群中检测到的情况相反。尽管如此，岛屿雏鸟的白细胞水平低于大陆鸟类，并且感染鹦鹉热衣原体的加那利群岛雏鸟表现出较差的细胞免疫反应。
结论/意义：环境和生态因素的综合作用可能有助于解释岛屿秃鹫对感染的高度易感性。此处所描述的情况在其他食腐动物种群数量急剧下降且受到严重威胁的岛屿系统中可能类似。在当前全球变化和新出现传染病数量不断增加的背景下，对感染的更高易感性可能是导致岛屿食腐动物灭绝的又一个决定性因素。
