The early maternal environment shapes the parental response to offspring UV ornamentation

Abstract

Parents allocate resources to offspring to increase their survival and to maximize their own fitness, while this investment implies costs to their condition and future reproduction. Parents are hence expected to optimally allocate their resources. They should invest equally in all their offspring under good conditions, but when parental capacity is limited, parents should invest in the offspring with the highest probability of survival. Such parental favouritism is facilitated by the fact that offspring have evolved condition-dependent traits to signal their quality to parents. In this study we explore whether the parental response to an offspring quality signal depends on the intrinsic capacity of the parents, here the female. We first manipulated the intrinsic capacity of blue tit (Cyanistes caeruleus) females through lutein-supplementation during egg laying, and we subsequently blocked the UV/yellow reflectance of breast feathers on half of the nestlings in each brood. We did not find evidence that the female intrinsic capacity shaped parental feeding or sibling competition according to offspring UV/yellow colouration. However, nestling UV/yellow colour affected costly behavioural interactions in the form of prey-testings (when a parent places a prey item into a nestling’s gape but removes it again). In lutein-supplemented nests, fathers but not mothers favoured UV-blocked chicks by testing them less often, supporting previous results. Accordingly, in lutein-supplemented nests, UV-blocked nestlings gained more mass than their siblings, while in control nests we found the opposite effect and UV-blocked nestlings gained less. Our results emphasize that the prenatal environment shaped the role of offspring UV/yellow colour during certain family interactions and are indicative for sex-specific parental care strategies.

Offspring plumage coloration as a condition‐dependent signal in the blue tit

“…Had these previous studies aimed at reducing total brightness (and not only UV chroma), they would have likely found stronger effects in intra‐family interactions. Indeed, given the large within‐nest effect of body mass on juvenile brightness, parents could rely on this trait to adjust their feeding strategies within their brood (García‐Campa et al, 2021 ; Mas & Kölliker, 2011 ; Morales & Velando, 2018 ). Therefore, total brightness could have evolved as a condition‐dependent trait to signal nestling quality to other family members.…”

“…This suggests that, at the intra-brood level, family members might not use UV chroma as a reliable signal of body mass. This was unexpected since we have experimentally demonstrated in the study population that chicks with reduced UV chroma gain less body mass (Morales & Velando, 2018) and that this trait is used as a signal during intra-family interactions (García-Antón et al, In press;García-Campa et al, 2021;Morales & Velando, 2018). Moreover, cavity-nesting passerines are especially good at detecting changes in UV reflectance (Avilés et al, 2006;Hunt et al, 2003;Wiebe & Slagsvold, 2009), which points to UV chroma as a promising candidate for a signal inside cavities.…”

“…Concretely, nestlings with experimentally blocked UV color beg more during feeding rates and in sib–sib competitive interactions (Morales & Velando, 2018 ). In addition, when resources are limited, parents favor chicks with higher UV chroma, thus, presumably those of high quality (García‐Campa et al, 2021 ; Morales & Velando, 2018 ). It is possible that the different components of colouration reveal different aspects of individual quality (Candolin, 2004 ), as they involve different dimensions of avian color perception (Jacot & Kempenaers, 2007 ): reflectance in the ultraviolet region of the spectrum (UV chroma; a measure of the contribution of UV to the total reflectance), carotenoid‐based reflectance (carotenoid chroma; which reflects the amount of carotenoid pigments deposited in feathers, as it represents the relative reflectance around the absorbance peak of carotenoids), and total reflectance (brightness).…”

Plumage colouration differs between offspring raised in natural cavities and nestboxes

“…However, in line with previous research, we found the presence of sexual dichromatism (both chroma and brightness) in blue tit nestling plumage (e.g., Jacot & Kempenaers, 2007) and lack thereof in great tits (Isaksson et al, 2008), suggesting a possible difference in the signalling role of this trait between species. Although still under debate, growing evidence points to a signalling function of nestling colouration in the blue tit (García-Campa et al, 2021; Morales & Velando, 2018), while in the great tit there is no evidence of parental preference towards more coloured nestlings (Tschirren et al, 2005).…”

“…To our knowledge, all studies on colouration of hole-nesters come from populations breeding in nestboxes or from birds kept in aviaries, which represents a significant knowledge gap. Despite the fact that the biological meaning of juvenile colouration is still debated, there are indications of its role in parent-offspring communication in both nesting and post-fledging period, informing adults on offspring quality and thus modulating parental provisioning effort (Tanner & Richner, 2008; Galván et al, 2008; Tschirren et al, 2003; Morales & Velando, 2018; García-Campa et al, 2021). Otherwise, it may play a role in establishing social hierarchies between juveniles, act as anti-predatory camouflage in bright deciduous forest (Slagsvold & Lifjeld, 1985; Tschirren et al, 2003), or be the by-product the expression of a genetic correlation with adult colouration (Drobniak et al, 2013).…”