Browsing by Author "Hauber, Mark E."

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Avian Eggshell Pigments Are Not Consistently Correlated With Colour Measurements or Egg Constituents in Two Turdus Thrushes
(Wiley, 2012) Cassey, Phillip; Miksik, Ivan; Portugal, Steven J.; Maurer, Golo; Ewen, John G.; Zarate, Erica; Hauber, Mark E.
The colourful appearance of avian eggshells is a prominent aspect of maternal reproductive effort in birds. Some differences in eggshell coloration have been reported to co-vary with various measures of maternal condition and these patterns support the hypothesis that, in some bird species, several aspects of eggshell colour (i.e. primary chroma and brightness) function as a signal of maternal and offspring quality to induce greater paternal investment. We directly quantified eggshell pigment concentrations of blackbird Turdus merula and song thrush T. philomelos eggshells and tested how the two key pigments (protoporphyrin IX and biliverdin) co-varied with other eggshell traits and egg constituents as measures of maternal reproductive investment, including total yolk carotenoid concentration, total lipid concentration, yolk mass, and shell thickness. Contrary to predictions, we detected few statistical patterns overall. We found that protoporphyrin IX concentration was negatively associated with blue-green chroma in blackbirds but not in song thrush. The concentration of protoporphyrin IX was significantly greater in blackbirds and also showed different patterns of association with total yolk lipids and yolk carotenoid concentrations between these two species (significant species interaction terms). Our results reveal that it is not appropriate to simply assume in these two avian species that reflectance-based eggshell colour measures are a suitable proxy for eggshell pigment concentrations or can be used as consistent predictors of maternal reproductive investment. These results highlight the need to assess and validate the strength and direction of the statistical relationships between eggshell colour measures, pigment concentrations, and maternal resource deposition in the egg for other species of birds.
Repeatability of Laboratory Measurements for Maternally Derived Yolk Carotenoid Concentrations in Bird Eggs
(Csiro Publishing, 2006) Cassey, Phillip; Ewen, John G.; Karadas, Filiz; Hauber, Mark E.
We describe a source of variability in maternally derived yolk carotenoids that is not routinely calculated in published studies. We quantify the measurement error in yolk carotenoid concentrations that may accrue during the analysis of yolk contents from repeat extractions and repeat high performance liquid chromatography (HPLC) runs of the same egg yolk sample from free range clutches of four farm bird species in New Zealand. We show that the variability between different eggs is substantially greater than the variability between replicate yolk extractions and HPLC analyses. Importantly, our results provide confidence to researchers that technical repeatability is a lesser concern when studying the biological differences between yolk samples.