Stable correlation structure among multiple plumage colour traits: can they work as a single signal?

Abstract

The presence of multiple distinct ornamental traits in the same species is frequently explained by contextspecificity and different information content. However, the expression of multiple ornaments is often correlated, and such traits may therefore function as a single, integrated signal. Delayed use of an integrated signal relative to production requires temporal stability in integration, which has seldom been examined. We used autumn and spring reflectance data from the breast, breast stripe, and crown of great tits (Parus major) to assess the stability and mating implications of colour signal integration, as well as the repeatability of any integrated colour trait and its correlation with condition during moult. We found high levels of stability between seasons, years, sexes, and ages in the correlation patterns of colour measures across the three plumage areas. The first principal component colour axis described joint variation of ultraviolet (UV) reflectance on the crown and the breast stripe, thereby representing an among-trait UV chroma axis. However, only breast yellow chroma showed condition-dependence, whereas temporally consistent and significant assortative mating was restricted to crown UV chroma. Our results therefore do not support the idea that the overall UV chroma of the breast stripe and the crown is special in condition-dependence and repeatability, or that it plays a specific role in mutual sexual selection as an integrated signal. The results show that stable association between display traits is an existing phenomenon. They also indicate that, even in the presence of correlated traits, functional trait integration among these requires further scrutiny.

Darker eggshell spotting indicates lower yolk antioxidant level and poorer female quality in the Eurasian Great Tit (Parus major)

“…Most females in our study were yearlings (2009: yearling n ¼ 12, adult n ¼ 1; 2011: yearling n ¼ 3, adult n ¼ 7, age unknown n ¼ 1; 2012: yearling n ¼ 22, adult n ¼ 0, age unknown n ¼ 3), so we did not have enough data for adult females to be able to test the effect of female age on eggshell pattern. Feather samples were collected from the black crown and breast stripe and the yellow breast (see details in Hegyi et al 2015), and stored in a dry, cool, and dark place until later spectrophotometric analysis. Blood samples (30-60 ll) were taken from the brachial veins of females and centrifuged at 10,000 rpm for 10 min on the same day.…”

“…For the black crown and black breast stripe, we calculated brightness (average reflectance, R 320-700 ) and UV chroma (R 320-400 /R 320-700 ), and for the yellow breast, we calculated brightness and yellow chroma ((R 700 -R 450 )/R 700 ). Because repeatabilities of measurements are high (Hegyi et al 2015), we used the average from each individuals' 3 scans in the following analyses. All plumage reflectance data from individuals analyzed in the present study were included in a larger (7-yr) dataset of plumage spectral data of our Great Tit population (Hegyi et al 2015).…”

“…Because repeatabilities of measurements are high (Hegyi et al 2015), we used the average from each individuals' 3 scans in the following analyses. All plumage reflectance data from individuals analyzed in the present study were included in a larger (7-yr) dataset of plumage spectral data of our Great Tit population (Hegyi et al 2015). Correlations among spectral traits have been found to be very consistent across years, seasons, sexes, and ages (Hegyi et al 2015).…”

“…All plumage reflectance data from individuals analyzed in the present study were included in a larger (7-yr) dataset of plumage spectral data of our Great Tit population (Hegyi et al 2015). Correlations among spectral traits have been found to be very consistent across years, seasons, sexes, and ages (Hegyi et al 2015). Therefore, in order to increase the reliability of our derived plumage color measures (principal components [PC] axes), we decided to use the axes obtained using the 7-yr dataset to describe plumage reflectance of individuals included in the present 3-yr dataset.…”

“…Second, we tested whether eggshell spotting pattern was related to the carotenoid-and melanin-based and nanostructural plumage coloration of females, which may indicate the intrinsic quality of the individual (Hõrak et al 2001, Galván 2011, Hegyi et al 2015). Third, we tested whether eggshell spotting pattern was related to the quality of the egg (yolk antioxidant level and yolk mass).…”