Talbott K M, Becker D J, Soini H A, Higgins B J, Novotny M V, Ketterson E D
Department of Biology, Indiana University, Bloomington, IN, U.S.A.
Department of Biology, University of Oklahoma, Norman, OK, U.S.A.
Anim Behav. 2022 Jun;188:147-155. doi: 10.1016/j.anbehav.2022.04.004. Epub 2022 May 11.
Investigating the impact of parasitism on host phenotype is key to understanding parasite transmission ecology, host behavioural ecology and host-parasite coevolution. Previous studies have provided evidence that avian odour is one such phenotypic trait, as mosquitoes that vector the haemosporidian blood parasite tend to prefer birds that are already infected. Preen oil is a major source of avian odour, yet studies to date have not identified differences in preen oil odour based on the presence or absence of haemosporidian infection. Because preen oil can vary with physiological dynamics, we predicted that the composition of preen oil odours might vary according to parasite load, rather than solely by the presence or absence of infection. We used gas chromatography-mass spectrometry to characterize the composition of volatile compounds in preen oil taken from female dark-eyed juncos, and asked whether their composition varied with relative haemosporidian parasite load, which we assessed using quantitative PCR. We identified a subset of volatile compounds (a 'blend') and two specific compounds that varied with increasing parasite load. Importantly, the quantity of these compounds did not vary based on parasite presence or absence, suggesting that birds with low parasite loads might be phenotypically indistinguishable from uninfected birds. The volatile blend associated with parasite load also varied with sampling date, suggesting a possible seasonal relapse of chronic infections triggered by shifts in junco host reproductive state. Furthermore, we found a positive relationship between parasite load and a volatile blend shown in a previous study to predict reproductive success in juncos. This is the first study to demonstrate quantitative differences in avian host odour based on haemosporidian parasite load. Our findings highlight the importance of focusing on parasite load, rather than solely presence or absence, in investigating host-parasite interactions.
研究寄生现象对宿主表型的影响是理解寄生虫传播生态学、宿主行为生态学以及宿主 - 寄生虫协同进化的关键。先前的研究已提供证据表明鸟类气味就是这样一种表型特征，因为传播血孢子虫血液寄生虫的蚊子往往更喜欢已被感染的鸟类。尾脂腺油是鸟类气味的主要来源，但迄今为止的研究尚未发现基于血孢子虫感染与否的尾脂腺油气味差异。由于尾脂腺油会随生理动态变化，我们预测尾脂腺油气味的成分可能会根据寄生虫负荷而变化，而非仅仅取决于感染的有无。我们使用气相色谱 - 质谱联用技术来表征从雌性暗眼灯草雀获取的尾脂腺油中挥发性化合物的成分，并询问其成分是否随血孢子虫相对寄生虫负荷而变化，我们通过定量聚合酶链反应来评估寄生虫负荷。我们鉴定出了一组挥发性化合物（一种“混合物”）以及两种随寄生虫负荷增加而变化的特定化合物。重要的是，这些化合物的量并非基于寄生虫的有无而变化，这表明寄生虫负荷低的鸟类在表型上可能与未感染的鸟类难以区分。与寄生虫负荷相关的挥发性混合物也随采样日期而变化，这表明灯草雀宿主繁殖状态的转变可能引发慢性感染的季节性复发。此外，我们发现寄生虫负荷与先前一项研究中显示可预测灯草雀繁殖成功率的一种挥发性混合物之间存在正相关关系。这是第一项证明基于血孢子虫寄生虫负荷的鸟类宿主气味存在定量差异的研究。我们的研究结果突出了在研究宿主 - 寄生虫相互作用时关注寄生虫负荷而非仅仅关注感染有无的重要性。
