Magallanes Sergio, Møller Anders Pape, Luján-Vega Charlene, Fong Esteban, Vecco Daniel, Flores-Saavedra Wendy, García-Longoriaa Luz, de Lope Florentino, Iannacone José A, Marzal Alfonso
Department of Anatomy, Cellular Biology and Zoology, University of Extremadura, Avda. de Elvas S/N, Badajoz ES-06006, Spain.
Ecologie Systématique Evolution, Université Paris-Sud, Orsay 91400, France.
Curr Zool. 2021 Apr;67(2):147-156. doi: 10.1093/cz/zoaa037. Epub 2020 Jul 16.
Parasites are globally widespread pathogenic organisms, which impose important selective forces upon their hosts. Thus, in accordance with the hypothesis, it is expected that defenses among hosts vary relative to the selective pressure imposed by parasites. According to the latitudinal gradient in diversity, species richness and abundance of parasites peak near the equator. The uropygial gland is an important defensive exocrine gland against pathogens in birds. Size of the uropygial gland has been proposed to vary among species of birds because of divergent selection by pathogens on their hosts. Therefore, we should expect that bird species from the tropics should have relatively larger uropygial glands for their body size than species from higher latitudes. However, this hypothesis has not yet been explored. Here, we analyze the size of the uropygial gland of 1719 individual birds belonging to 36 bird species from 3 Neotropical (Peru) and 3 temperate areas (Spain). Relative uropygial gland volume was 12.52% larger in bird species from the tropics than from temperate areas. This finding is consistent with the relative size of this defensive organ being driven by selective pressures imposed by parasites. We also explored the potential role of this gland as a means of avoiding haemosporidian infection, showing that species with large uropygial glands for their body size tend to have lower mean prevalence of haemosporidian infection, regardless of their geographical origin. This result provides additional support for the assumption that secretions from the uropygial gland reduce the likelihood of becoming infected with haemosporidians.
寄生虫是全球广泛分布的致病生物，它们对宿主施加重要的选择压力。因此，根据这一假说，可以预期宿主之间的防御能力会因寄生虫施加的选择压力而有所不同。根据多样性的纬度梯度，寄生虫的物种丰富度和丰度在赤道附近达到峰值。尾脂腺是鸟类抵御病原体的重要外分泌腺。由于病原体对宿主的不同选择，有人提出尾脂腺的大小在鸟类物种之间会有所不同。因此，我们应该预期热带地区的鸟类物种相对于其体型而言，尾脂腺会比高纬度地区的物种相对更大。然而，这一假说尚未得到探讨。在这里，我们分析了来自3个新热带地区（秘鲁）和3个温带地区（西班牙）的36种鸟类的1719只个体的尾脂腺大小。热带地区鸟类物种的相对尾脂腺体积比温带地区的大12.52%。这一发现与这种防御器官的相对大小受寄生虫施加的选择压力驱动相一致。我们还探讨了该腺体作为避免血孢子虫感染手段的潜在作用，结果表明，相对于其体型而言尾脂腺较大的物种，无论其地理来源如何，血孢子虫感染的平均患病率往往较低。这一结果为尾脂腺分泌物降低感染血孢子虫可能性的假设提供了额外支持。
