Egg Speckling Patterns Do Not Advertise Offspring Quality or Influence Male Provisioning in Great Tits

Abstract

Many passerine birds lay white eggs with reddish brown speckles produced by protoporphyrin pigment. However, the function of these spots is contested. Recently, the sexually selected eggshell coloration (SSEC) hypothesis proposed that eggshell color is a sexually selected signal through which a female advertises her quality (and hence the potential quality of her future young) to her male partner, thereby encouraging him to contribute more to breeding attempts. We performed a test of the SSEC hypothesis in a common passerine, the great tit Parus major. We used a double cross-fostering design to determine whether males change their provisioning behavior based on eggshell patterns they observe at the nest. We also tested the assumption that egg patterning reflects female and/or offspring quality. Because birds differ from humans in their color and pattern perception, we used digital photography and models of bird vision to quantify egg patterns objectively. Neither male provisioning nor chick growth was related to the pattern of eggs males observed during incubation. Although heavy females laid paler, less speckled eggs, these eggs did not produce chicks that grew faster. Therefore, we conclude that the SSEC hypothesis is an unlikely explanation for the evolution of egg speckling in great tits.

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

“…Similar to our results, egg color was not related to female body condition or body size in a Belgian population of Great Tits (De Coster et al 2013), in the Eurasian Kestrel (Martínez-Padilla et al 2010), the Ringbilled Gull (Larus delawarensis; Hanley and Doucet 2009), or the Eurasian Reed-Warbler (Krištofík et al 2013). By contrast, in British Great Tits (Stoddard et al 2012) and Blue Tits (Martínez-de la Puente et al 2007), heavier females laid less spotted eggs with paler spots. Although, in contrast to our timing of female measurement, which was similar to that of Martínez de la Puente et al (2007), Stoddard et al (2012) used body mass of females caught before breeding, their results were qualitatively similar if they used female mass during the nestling rearing period.…”

“…In contrast, Martínez-de la Puente et al (2007) found that Blue Tit females that laid less spotted eggs had better body condition and lower concentrations of stress proteins. In a study of British Great Tits (Parus major newtoni), it was found that heavier females laid paler eggs (Stoddard et al 2012). These latter studies support the view that darker pigmentation indicates poorer condition of the female.…”

“…By contrast, in British Great Tits (Stoddard et al 2012) and Blue Tits (Martínez-de la Puente et al 2007), heavier females laid less spotted eggs with paler spots. Although, in contrast to our timing of female measurement, which was similar to that of Martínez de la Puente et al (2007), Stoddard et al (2012) used body mass of females caught before breeding, their results were qualitatively similar if they used female mass during the nestling rearing period. If we applied these authors' measures of female body condition (body mass was used by Stoddard et al [2012]; body mass divided by the cube of tarsus length was used by Martínez-de la Puente et al…”

“…Several studies measured eggshell reflectance using a spectrophotometer and expressed it as brightness and red or brown chroma (Avilés et al 2007, Martínez-de la Puente et al 2007, Hanley and Doucet 2009, Maurer et al 2011b, Holveck et al 2012, Duval et al 2013, Krištofík et al 2013. 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.…”

Pattern recognition algorithm reveals how birds evolve individual egg pattern signatures

“…As phylogenetic constraints may also influence the evolution of certain egg patterns 7 , it will be important ultimately to investigate the extent of egg pattern replicability, distinctiveness and complexity in different avian lineages. Bird eggs are under diverse selection pressures 7,41 and this may additionally influence the type of signature that eventually evolves.…”