Effects of experimental calcium availability, egg parameters and laying order on Great TitParus majoreggshell pigmentation patterns

Abstract

Many bird species lay eggs speckled with protoporphyrin-based spots, however, for most of them the function of eggshell spotting is unknown. A plausible hypothesis is that protoporphyrin might have a structural function in strengthening the eggshell and is therefore deposited when calcium is scarce. In this study, we experimentally provided Great Tit Parus major females with supplemental calcium to examine its effect on the protoporphyrin-based maculation of their eggs. In addition, we studied variation in eggshell pigmentation patterns in relation to other egg parameters and laying order. Calcium-supplemented females laid larger eggs but shell thickness was not significantly affected by the treatment. Calcium supplementation may reduce the time and energy females devote to searching for calcium-rich material, so that they can collect more nutrients and so lay larger eggs. Furthermore, pigment darkness was associated with egg volume and shape, which suggests that female quality and environmental food availability may also influence the shell pigmentation pattern. Within clutches, later-laid eggs had larger and darker spots that were distributed more unevenly on the shell surface. This within-clutch pattern could be explained by the increase in egg volume and egg shape and a decline in shell thickness with egg-laying order, which characteristics were all related to shell-spotting pattern. Eggs with a coronal ring had thinner shells, but pigment intensity and spot size were not related to shell thickness. Thus, our results suggest that concentrated spotting distribution may have a mechanical function, supporting the structural-function hypothesis.

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

“…In additon, the Great Tit has no brood parasites, and birds do not eject distinct-looking eggs (Kempenaers et al 1995, R. Hargitai personal observation). In a previous study, we showed that the distribution of eggshell spots was related to eggshell thickness in our Great Tit population (Hargitai et al 2013), suggesting a structural function of shell pigmentation (Solomon 1997, Gosler et al 2005, but the intensity and size of spots were not related to eggshell thickness (Hargitai et al 2013). In this study, we first tested whether eggshell spotting pattern was related to female characteristics that may indicate condition and state of health (body condition, body size, plasma oxidative status, plasma leukocyte count, and clutch size).…”

“…Several hypotheses have been proposed to explain the pigmentation of bird eggshells (Kilner 2006, Reynolds et al 2009, Maurer et al 2011a); these hypotheses may not be mutually exclusive and could share similar predictions. Protoporphyrin-based eggshell pigmentation may promote camouflage (Stoddard et al 2011, Lovell et al 2013; it may enhance egg mimicry or permit egg recognition in species exposed to brood parasites (Stokke et al 1999, Soler et al 2000, Moskát et al 2008; it may help resist bacterial penetration into the egg (Ishikawa et al 2010, Fargallo et al 2014; or it may structurally strengthen eggshells (Gosler et al 2005, García-Navas et al 2010, Bulla et al 2012, Hargitai et al 2013, the latter of which is possibly the most plausible explanation for shell spotting patterns in cavity-nesting birds (Solomon 1997, Cherry andGosler 2010). Furthermore, Moreno and Osorno (2003) proposed that eggshell color could be a sexually selected signal, which may advertise the quality of the female and that of her offspring to the male parent in order that he contribute more to the breeding attempt (sexually selected eggshell coloration [SSEC] hypothesis).…”

“…Others determined pigment concentration of the eggshell by chemical analysis (Maurer et al 2011b, Cassey et al 2012, Duval et al 2013, Brulez et al 2014, or analyzed digitized pictures of eggshells to determine the percentage of spotted eggshell surface (Martínez-de la Puente et al 2007, Sanz and García-Navas 2009, Bulla et al 2012, Holveck et al 2012, Brulez et al 2014), or to determine hue, saturation, and brightness derived from HSB and RGB (Martínez-Padilla et al 2010, Cassey et al 2012, Holveck et al 2012), or to determine other spotting pattern variables, such as pattern contrast and marking size (Stoddard et al 2012). Finally, many studies used visual scoring of photographs, and spotting pattern was expressed as spot intensity, spot size, and spot distribution (Gosler et al 2005, Sanz and García-Navas 2009, López de Hierro and De Neve 2010, Bulla et al 2012, Holveck et al 2012, De Coster et al 2013, Hargitai et al 2013, Brulez et al 2014.…”

Effects of food limitation on the intensity of blue‐green and brown eggshell coloration: an experimental study with the canary

“…Moreover, it is possible that eggshell pigments modify the amount and wavelength of light transmitted through the eggshell and thus affect embryonic development (Maurer et al 2015, Lahti andArdia 2016), or they may play a thermoregulatory role (Bakken et al 1978, Westmoreland et al 2007). Pigments may also decrease trans-shell contamination by microbes (Ishikawa et al 2010, but see Fargallo et al 2014), or they may strengthen thin eggshells (Gosler et al 2005, García-Navas et al 2010, Hargitai et al 2013. Finally, according to the sexually selected eggshell coloration hypothesis Osorno 2003, Soler et al 2008), eggshell colour may signal the quality of the female to the male parent, and colour intensity could be used by males as a cue to determine their effort in parental care.…”

Effects of environmental conditions on the egg mass, yolk antioxidant level, eggshell thickness and eggshell spotting patterns of Great Tits (Parus major)

“…Protoporphyrinbased eggshell pigmentation may help to provide camouflage (Stoddard et al 2011), it may enhance egg mimicry or allow individual egg recognition in species exposed to brood parasites (Stokke et al 1999;Moskát et al 2008), it may reinforce eggshells (Gosler et al 2005;García-Navas et al 2010;Hargitai et al 2013), or it may signal the quality of the female and the egg to the male in order to stimulate more intense paternal care (Moreno and Osorno 2003;Sanz and García-Navas 2009;Stoddard et al 2012;Hargitai et al 2016b). The accumulation of protoporphyrin has been reported to induce oxidative stress, leading to an increase in the activity of antioxidant enzymes to avoid oxidative damage (Afonso et al 1999;Pimentel et al 2013).…”