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Thompson CF, Hodges KE, Mortimer NT, Vrailas-Mortimer AD, Sakaluk SK, Hauber ME. Avian eggshell coloration predicts shell-matrix protoporphyrin content. CAN J ZOOL 2022; 100:77-81. [PMID: 35185156 PMCID: PMC8855982 DOI: 10.1139/cjz-2021-0134] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2023]
Abstract
Avian eggshell pigmentation may provide information about a female's physiological condition, in particular her state of oxidative balance. Previously we found that female house wrens (Troglodytes aedon Vieillot, 1809) with lighter, less-maculated, and redder ground-colored shells were older and produced heavier offspring than females laying darker, browner eggs. The strong pro-oxidant protoporphyrin is responsible for this species' eggshell pigmentation, so differences in pigmentary coloration may be related to eggshell protoporphyrin content and reflect female oxidative balance and condition during egg-formation. Therefore, we tested the assumption that egg-surface coloration is related to the amount of protoporphyrin in the shell matrix. We analyzed digital photographs of eggs to determine maculation coverage as a measure of the overall ground coloration of the egg and its red-, green-, and blue-channel pixel values. Pigments were then extracted from these same eggs and analyzed using high-performance liquid chromatography. There was a strong, positive relationship between eggshell redness and protoporphyrin content of eggshells, but no relationship between percent maculation and protoporphyrin content. Thus, when older, larger females deposit more protoporphyrin in their eggshells, this may reflect a tolerance for high levels of circulating protoporphyrin or an effective mechanism for off-loading protoporphyrin into the eggshell matrix.
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Affiliation(s)
- Charles F Thompson
- School of Biological Sciences, Illinois State University, Normal, Illinois, USA
| | - Kara E Hodges
- School of Biological Sciences, Illinois State University, Normal, Illinois, USA
| | - Nathan T Mortimer
- School of Biological Sciences, Illinois State University, Normal, Illinois, USA
| | | | - Scott K Sakaluk
- School of Biological Sciences, Illinois State University, Normal, Illinois, USA
| | - Mark E Hauber
- Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, Illinois, USA
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Hauber ME, Bond AL, Kouwenberg AL, Robertson GJ, Hansen ES, Holford M, Dainson M, Luro A, Dale J. The chemical basis of a signal of individual identity: shell pigment concentrations track the unique appearance of Common Murre eggs. J R Soc Interface 2020; 16:20190115. [PMID: 30966949 DOI: 10.1098/rsif.2019.0115] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In group-living species with parental care, the accurate recognition of one's own young is critical to fitness. Because discriminating offspring within a large colonial group may be challenging, progeny of colonial breeders often display familial or individual identity signals to elicit and receive parental provisions from their own parents. For instance, the common murre (or common guillemot: Uria aalge) is a colonially breeding seabird that does not build a nest and lays and incubates an egg with an individually unique appearance. How the shell's physical and chemical properties generate this individual variability in coloration and maculation has not been studied in detail. Here, we quantified two characteristics of the avian-visible appearance of murre eggshells collected from the wild: background coloration spectra and maculation density. As predicted by the individual identity hypothesis, there was no statistical relationship between avian-perceivable shell background coloration and maculation density within the same eggs. In turn, variation in both sets of traits was statistically related to some of their physico-chemical properties, including shell thickness and concentrations of the eggshell pigments biliverdin and protoporphyrin IX. These results illustrate how individually unique eggshell appearances, suitable for identity signalling, can be generated by a small number of structural mechanisms.
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Affiliation(s)
- Mark E Hauber
- 1 Department of Animal Biology, School of Integrative Biology, University of Illinois , Urbana-Champaign, IL , USA.,2 American Museum of Natural History , New York, NY , USA
| | - Alexander L Bond
- 3 Bird Group, Department of Life Sciences, The Natural History Museum , Tring, Hertfordshire , UK
| | | | - Gregory J Robertson
- 5 Environment and Climate Change Canada , Mount Pearl, Newfoundland and Labrador , Canada
| | - Erpur S Hansen
- 6 South Iceland Nature Research Centre , Vestmannaeyjar , Iceland
| | - Mande Holford
- 2 American Museum of Natural History , New York, NY , USA.,7 Department of Chemistry, Hunter College and Graduate Center, City University of New York , New York, NY , USA
| | - Miri Dainson
- 1 Department of Animal Biology, School of Integrative Biology, University of Illinois , Urbana-Champaign, IL , USA
| | - Alec Luro
- 1 Department of Animal Biology, School of Integrative Biology, University of Illinois , Urbana-Champaign, IL , USA
| | - James Dale
- 8 School of Natural and Computational Sciences, Massey University , Auckland , New Zealand
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