Browsing by Author "Ewen, John G."

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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.
Condition Dependence of Nestling Mouth Colour and the Effect of Supplementing Carotenoids on Parental Behaviour in the Hihi (Notiomystis Cincta)
(Springer, 2008) Ewen, John G.; Thorogood, Rose; Karadas, Filiz; Cassey, Phillip
Carotenoids are integument pigments that often reflect foraging efficiency, disease resistance and body condition. In contrast to the widespread attention this relationship has received in adult birds, the condition dependence of nestling colouration remains an understudied component of animal communication. Here we assess the condition dependence of carotenoid pigmentation in nestling hihi (Notiomystis cincta, an endangered New Zealand bird) and examine the influence of carotenoid supplementation on nestling quality and parental visitation rates. Our results show that carotenoids provided to breeding adult hihi were transferred to their offspring and resulted in an intensified orange-yellow flange colour. After accounting for carotenoid supplementation the parameter that most consistently explained variation in nestling flange colour was nestling tarsus length at 23 days, indicating condition dependence of this trait. We did not, however, detect direct effects of carotenoid supplementation on nestling mass or immune response (or any other fitness parameter measured). Carotenoid supplementation did, however, result in an increased paternal provisioning rate.
Foraging for Carotenoids: Do Colorful Male Hihi Target Carotenoid-Rich Foods in the Wild
(Oxford Univ Press inc, 2014) Walker, Leila K.; Thorogood, Rose; Karadas, Filiz; Raubenheimer, David; Kilner, Rebecca M.; Ewen, John G.
Dietary access to carotenoids is expected to determine the strength of carotenoid-based signal expression and potentially to maintain signal honesty. Species that display carotenoid-based yellow, orange, or red plumage are therefore expected to forage selectively for carotenoid-rich foods when they are depositing these pigments during molt, but whether they actually do so is unknown. We set out to address this in the hihi (Notiomystis cincta), a New Zealand passerine where males, but not females, display yellow carotenoid-based plumage. We measured circulating carotenoid concentrations in male and female hihi during breeding and molt, determined the nutritional content of common foods in the hihi diet, and conducted feeding observations of male and female hihi during molt. We found that although male and female hihi do not differ significantly in plasma carotenoid concentration, male hihi have a greater proportion of carotenoid-rich foods in their diet than do females. This is a consequence of a greater fruit and lower invertebrate intake than females and an avoidance of low-carotenoid content fruit. By combining behavioral observations with quantification of circulating carotenoids, we present evidence that colorful birds forage to maximize carotenoid intake, a conclusion we would not have drawn had we examined plasma carotenoids alone.
Maternally Invested Carotenoids Compensate Costly Ectoparasitism in the Hihi
(Natl Acad Sciences, 2009) Ewen, John G.; Thorogood, Rose; Brekke, Patricia; Cassey, Phillip; Karadas, Filiz; Armstrong, Doug P.
Dietary ingested carotenoid biomolecules have been linked to both improved health and immunity in nestling birds. Here, we test whether maternally invested egg carotenoids can offset the cost of parasitism in developing nestling hihi (Notiomystis cincta) from the bloodsucking mite (Ornithonyssus bursa). Our results reveal clear negative effects of parasitism on nestlings, and that maternally derived carotenoids compensate this cost, resulting in growth parameters and ultimate mass achieved being similar to nonparasitized young. Our results offer an unique example of a direct positive relationship between enhanced maternal investment of carotenoids and an ability to cope with a specific and costly parasite in young birds. As O. bursa infestations reduce population viability in hihi, our findings also highlight the importance of key nutritional resources for endangered bird populations to better cope with common parasite infestations.
A Nondestructive Method for Extracting Maternally Derived Egg Yolk Carotenoids
(Wiley, 2007) Cassey, Phillip; Ewen, John G.; Boulton, Rebecca L.; Karadas, Filiz; Moller, Anders P.; Blackburn, Tim M.
Maternally deposited carotenoids are a prominent component of egg yolk and are vital for the development and growth of the embryo. In most studies of avian yolk carotenoids, eggs are destructively sampled and this may limit both the number of clutches studied and the research questions addressed. We describe an empirical field trial for a nondestructive biopsy method to extract small samples (0.05 ml) of egg yolk for high-performance liquid chromatography (HPLC) analysis of yolk carotenoid concentrations. We sampled 180 clutches (N= 44 biopsies) of two species of introduced thrushes (genus Turdus) from agricultural habitats in central North Island, New Zealand. Once the protocol was established, all biopsied eggs from clutches that were not depredated or deserted before candling were found to be developing normally after 3-5 d of incubation (N= 28) and all hatched. Biopsy samples (> 0.02 g) produced concentrations of yolk carotenoids (and variances) that were statistically indistinguishable from whole yolk destructive samples. In addition, our samples (> 0.02 g) confirmed previously reported differences in yolk carotenoid concentrations between the two thrush species and revealed a significant decline in yolk carotenoid concentration with laying order. Further examination of how variability in yolk carotenoid concentration and identity influences offspring sex, success, and survival or, later in life, reproductive success and ability to efficiently incorporate dietary carotenoids into both integument and immune tissues will require larger sample sizes. Studies to date have been restricted by the number of destructive samples that investigators are willing (or permitted) to obtain from wild species. Thus, we hope that our nondestructive method of sampling yolk will promote further examination of the links between carotenoid uptake from the environment and maternal investment in the avian yolk.
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.
A Window on the Past: Male Ornamental Plumage Reveals the Quality of Their Early-Life Environment
(Royal Soc, 2013) Walker, Leila K.; Stevens, Martin; Karadas, Filiz; Kilner, Rebecca M.; Ewen, John G.
It is well established that the expression of many ornamental traits is dependent on the current condition of the bearer. However, conditions experienced in early life are also known to be important for an individual's subsequent fitness and therefore, directly or indirectly, for the fitness of their mate. Specifically, a recent hypothesis suggests that sexually selected traits might be sensitive to conditions experienced during early-life development and thereby function as honest indicators of developmental history. Whether this applies to colourful male plumage, however, is largely unknown. We tested this idea with a field experiment by manipulating neonatal nutrition in a sexually dichromatic passerine, the hihi (Notymystis cincta). We found that carotenoid supplementation increased nestling plasma carotenoid concentration, which was in turn correlated with increased yellow saturation in male breeding plumage after moulting. We also found that the post-moult luminance (lightness) of the white ear-tufts tended to be reduced in males that had received an all-round nutritional supplement as nestlings. Black breeding plumage was not affected by neonatal nutritional treatment. Although the mechanisms that generate colourful plumage are evidently diverse, our results show that at least some parts of this display are accurate indicators of environmental conditions during development.