Hamble_07_08_2ages from Avian malaria-mediated population decline of a widespread iconic bird species

Parasites have the capacity to affect animal populations by modifying host survival, and it is increasingly recognized that infectious disease can negatively impact biodiversity. Populations of the house sparrow (<i>Passer domesticus</i>) have declined in many European towns and cities, but the causes of these declines remain unclear. We investigated associations between parasite infection and house sparrow demography across suburban London where sparrow abundance has declined by 71% since 1995. <i>Plasmodium relictum</i> infection was found at higher prevalences (averaging 74%) in suburban London house sparrows than previously recorded in any wild bird population in Northern Europe. Survival rates of juvenile and adult sparrows and population growth rate were negatively related to <i>Plasmodium relictum</i> infection intensity. Other parasites were much less prevalent and exhibited no relationship with sparrow survival and no negative relationship with population growth. Low rates of co-infection suggested sparrows were not immunocompromised. Our findings indicate that <i>P. relictum</i> infection may be influencing house sparrow population dynamics in suburban areas. The demographic sensitivity of the house sparrow to <i>P. relictum</i> infection in London might reflect a recent increase in exposure to this parasite.

寄生虫可通过改变宿主存活率对动物种群产生影响，当前学界日益达成共识：传染性疾病会对生物多样性造成负面影响。许多欧洲城镇的家麻雀（house sparrow, *Passer domesticus*）种群数量均出现下滑，但其种群衰退的具体诱因至今尚未明确。本研究针对伦敦郊区的家麻雀种群展开调查，该区域自1995年以来家麻雀的种群丰度已下降71%，旨在探究寄生虫感染与家麻雀种群动态之间的关联。
研究发现，伦敦郊区家麻雀的里氏疟原虫（Plasmodium relictum）感染率高达74%（平均水平），这一感染率高于此前北欧地区所有野生鸟类种群的记录值。家麻雀幼体与成体的存活率以及种群增长率，均与里氏疟原虫的感染强度呈负相关关系。其余寄生虫的感染率则显著更低，且未发现其与家麻雀存活率存在关联，亦未对种群增长率产生负面影响。混合感染率较低的现象表明，家麻雀并未出现免疫功能受损的情况。
本研究结果显示，里氏疟原虫（*P. relictum*）感染或正在影响郊区家麻雀的种群动态。伦敦地区家麻雀对里氏疟原虫感染的种群动态敏感性，或反映出该种群近期接触该寄生虫的概率有所上升。