Abstract

The significance of colour signals in species with strong sexual dimorphism and/or elaborated visual ornaments is rather well-understood. Less attention has, however, been devoted to study colour signals in species with weak or no apparent sexual dimorphism. In such species, an interesting possibility arises as both sexes can bear the same colour ornament(s) (i.e. sexes are mutually ornamented), but their signalling value might differ in males and females. We aimed to explore this possibility by investigating the phenotypic correlates of the black bib, a melanin-based plumage ornament, in the Eurasian tree sparrow (Passer montanus). More specifically, we studied the sex-dependent relationships between bib size and three aspects of individuals’ phenotype: body condition (i.e. size-corrected body mass), physiology (i.e. cellular innate immunity/inflammation status, expressed through total leucocyte counts, and chronic physiological stress, expressed through the ratio of heterophils to lymphocytes) and individual personality (i.e. activity in a novel environment). We found that bib size was not associated with body condition and cellular innate immunity/inflammation status, but was positively related to physiological stress levels independent of sex. Furthermore, bib size was negatively associated with activity in males but positively in females. Our findings bring important correlative evidence that mutual ornamental traits may have sex-specific signalling value.

Significance statement

The signalling role of elaborated colourful ornaments, that are usually possessed only by males in sexually dimorphic species, is well-established. The function of various colour traits which are borne by both sexes (i.e. mutual ornaments), however, is less obvious. Do they have a signalling value in both sexes? If yes, do they signal the same information in males and females? Or, most intriguingly, can they convey different information in the two sexes? To test these alternatives, we studied the signalling value of the black bib, a melanin-based mutual plumage ornament, in Eurasian tree sparrows (Passer montanus). Apart from being correlated with chronic stress in both sexes, bib size was positively related to activity in females but negatively in males. Our results suggest that the information content of the same colour trait in males and females can be different in mutually ornamented species.

中文翻译：

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雀形目中相互羽毛装饰的个性特定性别信号

摘要

色信号在具有强烈的性二态性和/或精致的视觉装饰的物种中的重要性是相当容易理解的。然而，较少的注意力投入到研究具有弱性或没有明显性二态性的物种中的颜色信号上。在这样的物种中，出现了一种有趣的可能性，因为两性都可以带有相同颜色的装饰品（即，两性相互装饰），但是它们的信号传递价值在雄性和雌性中可能有所不同。我们旨在通过调查欧亚树麻雀（Passer montanus）黑色围兜（一种基于黑色素的羽毛装饰物）的表型相关性来探索这种可能性。）。更具体地说，我们研究了围兜大小与个体表型的三个方面之间的性别相关关系：身体状况（即，大小校正后的体重），生理学（即，细胞的先天免疫/炎症状态，通过总白细胞计数表达）和慢性生理压力，通过嗜异性细胞与淋巴细胞的比例和个人个性（即在新环境中的活动）来表示。我们发现围兜大小与身体状况和细胞先天免疫/炎症状态无关，但与生理压力水平正相关，而与性别无关。此外，围兜的大小与男性活动呈负相关，而与女性活动呈正相关。我们的发现带来了重要的相关证据，表明相互的装饰性状可能具有特定于性别的信号传导价值。

重要性声明

精心制作的彩色装饰物（通常仅由雄性有性双态物种拥有）的信号传导作用已得到充分确立。但是，男女共同承担的各种颜色特征的功能（即相互装饰）不太明显。他们在男女中都有信号价值吗？如果是，它们是否在男性和女性中传达相同的信息？或者，最有趣的是，他们能否在两个性别中传达不同的信息？为了测试这些替代方案，我们研究了欧亚树麻雀（Passer montanus）中黑色围兜（一种基于黑色素的相互羽毛装饰）的信号传递价值。）。围兜的大小除了与男性的慢性压力相关外，与女性的活动量呈正相关，而与男性的活动呈负相关。我们的结果表明，在相互装饰的物种中，雄性和雌性相同颜色性状的信息含量可能不同。