Rohwer Vanya G, Rohwer Sievert, Wingfield John C
Cornell University Museum of Vertebrates, Ithaca, NY 14850, USA.
Burke Museum of Natural History and Culture and Department of Biology, University of Washington, Seattle, WA 98195, USA.
R Soc Open Sci. 2020 Feb 12;7(2):191510. doi: 10.1098/rsos.191510. eCollection 2020 Feb.
Aggression in territorial social systems is easy to interpret because the benefits of territorial defence mostly accrue to the territorial holder. However, in non-territorial systems, high aggression seems puzzling and raises intriguing evolutionary questions. We describe extreme rates of despotism between age classes in a passerine bird, the painted bunting (), during the pre-moulting period. Aggressive encounters were not associated with aggressors gaining immediate access to resources. Instead, conspecifics, and even other species, were pursued as though being harassed; this aggression generated an ideal despotic habitat distribution such that densities of adult males were higher in high-quality sites. Aggression was not a by-product of elevated testosterone carried over from the breeding season but, rather, appeared associated with dehydroepiandrosterone, a hormone that changes rates of aggression in non-breeding birds without generating the detrimental effects of high testosterone titres that control aggression in the breeding season. This extraordinary pre-moult aggression seems puzzling because individual buntings do not hold defined territories during their moult. We speculate that this high aggression evolved as a means of regulating the number of conspecifics that moulted in what were historically small habitat patches with limited food for supporting the extremely rapid moults of painted buntings.
在领地性社会系统中，攻击行为很容易解释，因为领地防御的益处大多归于领地占有者。然而，在非领地性系统中，高度攻击性似乎令人费解，并引发了有趣的进化问题。我们描述了在换羽前期，一种雀形目鸟类——彩鹀（Passerina ciris）不同年龄组之间极端的专制率。攻击性遭遇与攻击者立即获取资源并无关联。相反，同种个体甚至其他物种会像受到骚扰一样被追逐；这种攻击行为产生了一种理想的专制性栖息地分布，使得成年雄性在优质栖息地的密度更高。攻击行为并非繁殖季节遗留的睾酮水平升高的副产品，而是似乎与脱氢表雄酮有关，这种激素会改变非繁殖期鸟类的攻击率，而不会产生高睾酮水平在繁殖季节控制攻击行为时带来的有害影响。这种换羽前的异常攻击行为似乎令人费解，因为彩鹀个体在换羽期间并不占据明确的领地。我们推测，这种高度攻击性的进化是作为一种调节同种个体数量的手段，这些个体在历史上栖息地面积小、食物有限的区域换羽，而这些区域要支持彩鹀极其快速的换羽过程。
