A small badge of longevity: opposing survival selection on the size of white and black wing markings

Abstract

According to handicap principle, exaggerated ornamental traits are supposed to exert costs on their bearers. However, there is much less theoretical and practical consensus about whether and under which conditions ornament expression should positively correlate with survival. We measured age‐related variation and survival selection on the size of white wing patches and black wing tips in a long‐lived monogamous seabird, the common gull Larus canus. Males had larger white patches than females but patch size showed concave relationship with age irrespective of sex, suggesting that white patch size was prone to senescence in both sexes. Extent of wing tip abrasion correlated negatively with the size of white patch, suggesting, in agreement with the Zahavian handicap hypothesis that only individuals with largest ornaments are able of maintaining them and not paying cost of displaying them. Areas of white wing patches and black wing tips correlated negatively. Irrespective of sex, survival selection favored birds with larger white wing patches and smaller black wing tips, which suggests that white and black wing markings may have coevolved as reverse components of a single ornament. Altogether, our results provide an evidence for the case where survival selection on ornamental traits in females is not weaker than in males. Absence of sex differences with respect to most of observed patterns is consistent with a prediction that among monogamous long‐lived species with biparental care, mutual mate choice leads to evolution of elaborate ornamental traits in both sexes.

Uropygial gland size: a marker of phenotypic quality that shows no senescence in a long-lived seabird

“…Middle-aged birds started egg-laying and had larger wing patches than young and old individuals. This result is consistent with the previous findings of the longitudinal studies from the same population, demonstrating senescence in annual fitness (Rattiste 2004;Brommer and Rattiste 2008) and wing patch size (Sepp et al 2017). Previous study in the same population (Sepp et al 2017) suggested that size of the white wing patch in common gulls may serve as an honest handicap signal of individual quality: possessing unpigmented areas in the tip of the wing is probably costly as feather breakage is more likely in the sites that lack protection by melanin (reviewed by Burtt 1986).…”

“…This result is consistent with the previous findings of the longitudinal studies from the same population, demonstrating senescence in annual fitness (Rattiste 2004;Brommer and Rattiste 2008) and wing patch size (Sepp et al 2017). Previous study in the same population (Sepp et al 2017) suggested that size of the white wing patch in common gulls may serve as an honest handicap signal of individual quality: possessing unpigmented areas in the tip of the wing is probably costly as feather breakage is more likely in the sites that lack protection by melanin (reviewed by Burtt 1986). Thus only individuals in superior condition (that being, for example, stronger feather structure, more protective preen gland, or ability to avoid situations where feathers may break) can afford large unpigmented areas in wingtips, and the size of these areas enables them to signal their prime condition (Zahavi 1975).…”

“…Thus only individuals in superior condition (that being, for example, stronger feather structure, more protective preen gland, or ability to avoid situations where feathers may break) can afford large unpigmented areas in wingtips, and the size of these areas enables them to signal their prime condition (Zahavi 1975). Consistent with signalling function of white wing patches are the findings that their size was positively related to survival and that individuals with larger white wing patches experienced lower extent of abrasion of wing tips (Sepp et al 2017). It is thus most likely that the later start of breeding and smaller wing patches of old common gulls reflect senescence of reproductive and signal traits.…”

“…For that matter, we measured uropygial gland size in male and female common gulls (Larus canus), aged from 2 to 28 years, in a cross-sectional manner. Previous studies in this species have indicated that reproductive senescence is common in this colony, with old birds starting breeding later and having lower breeding success (Brommer and Rattiste 2008), lower investment into egg quality (Urvik et al 2018) and having smaller ornamental white wing patches (Sepp et al 2017) than middle-aged birds. At the same time, traits related to physiological condition (telomere length and skin pentosidine concentration; Rattiste et al 2015), and indices of oxidative and nutritional state (Urvik et al 2016), do not show consistent age-related patterns.…”

“…All birds were photographed with their right wing pressed against a flat surface with a ruler placed next to it for scale ( Fig. 1, see Sepp et al 2017 for method details). White wing patch area, a sexually dimorphic measure of wing ornamentation, was measured in mm 2 from digital photographs using IMAGEJ software (http://rsbweb.nih.gov).…”