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Szala K, Tobolka M, Surmacki A. Presence of the cloud cover and elevation angle of the sun affect measurements of eggshell coloration and patterning obtained from calibrated digital images. Ecol Evol 2023; 13:e10170. [PMID: 37435021 PMCID: PMC10329936 DOI: 10.1002/ece3.10170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 05/15/2023] [Accepted: 05/24/2023] [Indexed: 07/13/2023] Open
Abstract
Calibrated digital photography is frequently used in studies focusing on avian eggshell appearance to measure colour and pattern features. Photographs are often taken in natural light conditions, yet little is known to what extent the normalisation process is able to control for varied light. Here, we photographed 36 blown eggs of the Japanese quail Coturnix japonica at five different elevation angles of the sun on both sunny and uniformly overcast days alongside grey standards. We normalised and processed the photographs in the MICA Toolbox software and checked how much noise was introduced by different natural light conditions to the colour and pattern measurements of the same set of eggs. Our results indicate that natural variation of light conditions affects eggshell colour and pattern measurements obtained by means of calibrated digital photography. Depending on a trait, the elevation angle of the sun had similar or even greater effect on the measurement than the presence of the cloud cover. Furthermore, measurements taken in cloudy conditions were more repeatable than those taken in sunny conditions. Based on the results, we propose practical guidelines regarding measuring colour and pattern of eggshells using calibrated digital photography in outdoor conditions.
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Affiliation(s)
- Klaudia Szala
- Department of Avian Biology and Ecology, Faculty of BiologyAdam Mickiewicz UniversityPoznańPoland
| | - Marcin Tobolka
- Department of ZoologyPoznań University of Life SciencesPoznańPoland
- Konrad Lorenz Institute of Ethology, University of Veterinary Medicine ViennaViennaAustria
| | - Adrian Surmacki
- Department of Avian Biology and Ecology, Faculty of BiologyAdam Mickiewicz UniversityPoznańPoland
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2
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Research progress on bird eggshell quality defects: a review. Poult Sci 2022; 102:102283. [PMID: 36399932 PMCID: PMC9673113 DOI: 10.1016/j.psj.2022.102283] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 10/18/2022] [Accepted: 10/18/2022] [Indexed: 11/05/2022] Open
Abstract
The eggshell quality declined with extending of chicken laying cycles. Eggshell quality is a crucial feature that not only affects consumer preference, but also influences producers' economic profitability. The eggshell ultrastructure consists of mammillary, palisade, and vertical crystal layers. Any defect in shell structure results in a reduction in eggshell quality. Speckled, translucent, pimpled, and soft eggshells are common defects that cause significant financial losses for farmers and food security concerns for consumers. Therefore, reducing the faulty eggshells is critical for poultry production. Defective eggshell quality has been attributed to hereditary factors and external environmental stimuli. As such, improvements can be carried out through selective breeding and environmental control of components such as temperature, moisture, and diet formula balance. In this review, the molecular mechanisms of the main eggshell quality defects (speckled, translucent, pimpled, broken, and soft-shell eggs) and the relevant improvement methods are detailed. We hope this review will serve as a useful resource for poultry production management and effectively increasing eggshell quality.
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3
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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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4
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Díaz-Lora S, Pérez-Contreras T, Azcárate-García M, Peralta-Sánchez JM, Martínez-Bueno M, José Soler J, Martín-Vivaldi M. Cosmetic coloration of cross-fostered eggs affects paternal investment in the hoopoe ( Upupa epops). Proc Biol Sci 2021; 288:20203174. [PMID: 33947236 PMCID: PMC8097196 DOI: 10.1098/rspb.2020.3174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Accepted: 04/06/2021] [Indexed: 11/12/2022] Open
Abstract
The signalling hypothesis suggests that avian eggshell coloration is a sexually selected female signal advertising her quality to its male partner, thereby stimulating his provisioning rate. This hypothesis has been tested for structural eggshell pigments, but not for cosmetic colorations, such as that produced by the uropygial secretion on eggshells. During the breeding season, female hoopoes (Upupa epops) host in their uropygial glands symbiotic bacteria. Females actively smear the eggshells with their secretion, protecting embryos from pathogenic trans-shell infections and changing eggshell coloration. Because the colour of the secretions is related to their antimicrobial potential, cosmetic eggshell coloration may act as a cue or even as a post-mating sexually selected signal if it affects male provisioning rates. To experimentally test this hypothesis, we cross-fostered already-smeared clutches between hoopoe nests, and quantified male feeding behaviour to females before and after the experiment. This approach allows disentanglement of the effects of female quality and of egg coloration on male investment. In accordance with the hypothesis, males adjusted their provisioning rate to the eggshell cosmetic coloration. This is, to our knowledge, the first experimental demonstration that egg colour stained with uropygial secretion could act as a post-mating sexual signal of female quality to males.
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Affiliation(s)
- Silvia Díaz-Lora
- Departamento de Zoología, Facultad de Ciencias, Universidad de Granada (UGR), Granada, Spain
| | - Tomás Pérez-Contreras
- Departamento de Zoología, Facultad de Ciencias, Universidad de Granada (UGR), Granada, Spain
- Unidad asociada: Coevolución: cucos, hospedadores y bacterias simbiontes, Universidad de Granada (UGR), Granada, Spain
| | - Manuel Azcárate-García
- Departamento de Ecología Funcional y Evolutiva, Estación Experimental de Zonas Áridas (EEZA-CSIC), Almería, Spain
| | | | - Manuel Martínez-Bueno
- Departamento de Microbiología, Facultad de Ciencias, Universidad de Granada (UGR), Granada, Spain
- Unidad asociada: Coevolución: cucos, hospedadores y bacterias simbiontes, Universidad de Granada (UGR), Granada, Spain
| | - Juan José Soler
- Unidad asociada: Coevolución: cucos, hospedadores y bacterias simbiontes, Universidad de Granada (UGR), Granada, Spain
- Departamento de Ecología Funcional y Evolutiva, Estación Experimental de Zonas Áridas (EEZA-CSIC), Almería, Spain
| | - Manuel Martín-Vivaldi
- Departamento de Zoología, Facultad de Ciencias, Universidad de Granada (UGR), Granada, Spain
- Unidad asociada: Coevolución: cucos, hospedadores y bacterias simbiontes, Universidad de Granada (UGR), Granada, Spain
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5
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Liu Y, Ren X, Yu H, Cheng Y, Guo Y, Yao W, Xie Y. Non-destructive and online egg freshness assessment from the egg shell based on Raman spectroscopy. Food Control 2020. [DOI: 10.1016/j.foodcont.2020.107426] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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6
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Hodges KE, Mortimer NT, Vrailas-Mortimer AD, Sakaluk SK, Thompson CF. Connecting the dots: avian eggshell pigmentation, female condition and paternal provisioning effort. Biol J Linn Soc Lond 2020; 130:114-127. [PMID: 32394988 DOI: 10.1093/biolinnean/blaa002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 01/03/2020] [Accepted: 01/04/2020] [Indexed: 12/13/2022]
Abstract
Differences in avian eggshell pigmentation could be an honest signal of female quality that males use to inform their nestling provisioning effort. We investigated whether among-individual variation in protoporphyrin-based eggshell pigmentation in house wrens (Troglodytes aedon) reflects female fitness-associated traits and whether males use that information. Females laying lighter clutches were older and larger than females laying darker clutches. Nestlings hatching from lighter clutches had greater size-corrected mass on post-hatch day 11, a measure that strongly predicts survival and recruitment to the breeding population. To test whether male provisioning effort responds to clutch pigmentation, we used a reciprocal clutch cross-fostering design, swapping dark with light clutches and light with dark; in controls, we swapped light with light clutches and dark with dark. Shortly before hatching, clutches were returned to their original nest to avoid confounding effects of nestling quality on male provisioning. Contrary to the sexual selection hypothesis, clutch pigmentation had no effect on male provisioning. Males were probably able to observe eggshell pigmentation and thus had information about female quality, but they did not use this information to modulate their nestling provisioning. This may be because of constraints on species-specific reproductive opportunities, or because variation in eggshell protoporphyrin serves other functions.
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Affiliation(s)
- Kara E Hodges
- School of Biological Sciences, Illinois State University,Normal,IL,USA
| | - Nathan T Mortimer
- School of Biological Sciences, Illinois State University,Normal,IL,USA
| | | | - Scott K Sakaluk
- School of Biological Sciences, Illinois State University,Normal,IL,USA
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Ding J, Yang W, Yang Y, Ai S, Bai X, Zhang Y. Variations in tree sparrow (Passer montanus) egg characteristics under environmental metal pollution. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 687:946-955. [PMID: 31412498 DOI: 10.1016/j.scitotenv.2019.06.140] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Revised: 06/08/2019] [Accepted: 06/08/2019] [Indexed: 06/10/2023]
Abstract
Environmental metal pollution is known to adversely affect bird reproduction, for which the variations of egg characteristics are considered very important. Our study explored whether variations in egg characteristics, such as egg volume, eggshell spotting pattern, eggshell coloration, and eggshell thickness, were correlated with heavy metal levels (Cu, Zn, Pb, and Cd) and Ca levels in the eggshells of tree sparrows (Passer montanus), a widespread passerine species. Eggs were collected from a long-term heavy metal polluted area (Baiyin, BY, northwest China) and a relatively unpolluted area (Liujiaxia, LJX, northwest China). Our results showed that the embryonated (eggshell: Cu: p = 0.003, Pb: p = 0.002) and non-embryonated (egg contents: Pb: p = 0.044, Ca: p = 0.045) eggs collected from BY contained relatively higher metal concentrations than those from LJX. Eggs from BY were smaller in volume (p < 0.01) and thinner in eggshell thickness (p < 0.01) than those from LJX. Mean egg volume increased with clutch size in BY (p = 0.017), which was also accompanied by an increase in the within-clutch coefficient of variation (CV) for egg volume (p = 0.045). Clutches with a higher CV for egg volume tended to contain higher concentrations of Zn and Pb (Zn: p = 0.084; Pb: p = 0.081) in the eggshells from BY. No differences were found in the eggshell spotting coverage ratio of eggs; however, eggshells were much darker in BY than in LJX. A more aggregated eggshell spotting distribution indicated higher eggshell Zn and Pb levels (BY: Zn: p = 0.040, Pb: p = 0.076; LJX: Pb: p = 0.066). The results demonstrate that the egg characteristics of tree sparrows can be used as indicators of metal pollution, especially for the within-clutch CV for egg volume, eggshell spotting pattern and eggshell coloration.
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Affiliation(s)
- Jian Ding
- Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Wenzhi Yang
- Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Ying Yang
- Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Shiwei Ai
- School of Public Health, Lanzhou University, Lanzhou 730000, China
| | - Xiaojuan Bai
- Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Yingmei Zhang
- Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University, Lanzhou 730000, China.
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Holveck MJ, Guerreiro R, Perret P, Doutrelant C, Grégoire A. Eggshell coloration indicates female condition during egg-laying: a field experiment in blue tits. Biol J Linn Soc Lond 2019. [DOI: 10.1093/biolinnean/blz082] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
AbstractSeveral selection pressures may explain the evolution of avian eggshell coloration patterns. In cavity-nesting species, there are two main non-exclusive hypotheses. The sexually selected eggshell colour hypothesis proposes that eggshell coloration is a sexually selected signal of female and offspring quality used by males that influences paternal care or future re-mating decisions. The structural function hypothesis proposes that pigments help strengthen the eggshell and are present at higher levels and at the blunt end of the egg when females face calcium shortages. We tested whether eggshell coloration (brown spots on a white ground colour) in blue tits (Cyanistes caeruleus) could reliably indicate female condition at laying by forcing females to produce two consecutive clutches, thus increasing their reproductive costs. Three measures of eggshell coloration – the area covered by spots as well as white ground UV-chroma and brightness – changed between clutches; the fourth measure, spot distribution, did not. The changes were more dramatic in young and lower-quality females. All the measures varied with female quality (i.e. body condition and/or laying date). Overall, higher-quality females produced more colourful (larger, more concentrated spotted surface area; higher UV-chroma) and less bright (i.e. putatively more pigmented) eggshells, a result that is generally in line with past research. We found a clear empirical link between eggshell coloration and female condition in blue tits, an important step in determining whether eggshell coloration is a sexual signal, but which does not exclude a potential concomitant structural function.
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Affiliation(s)
- Marie-Jeanne Holveck
- CEFE UMR 5175, Univ Montpellier, CNRS, Univ Paul Valéry Montpellier 3, EPHE, IRD, Montpellier, France
| | - Romain Guerreiro
- CEFE UMR 5175, Univ Montpellier, CNRS, Univ Paul Valéry Montpellier 3, EPHE, IRD, Montpellier, France
| | - Philippe Perret
- CEFE UMR 5175, CNRS, Univ Montpellier, Univ Paul Valéry Montpellier 3, EPHE, IRD, Montpellier, France
| | - Claire Doutrelant
- CEFE UMR 5175, CNRS, Univ Montpellier, Univ Paul Valéry Montpellier 3, EPHE, IRD, Montpellier, France
| | - Arnaud Grégoire
- CEFE UMR 5175, Univ Montpellier, CNRS, Univ Paul Valéry Montpellier 3, EPHE, IRD, Montpellier, France
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Hoi H, Darolová A, Krištofík J, Poláček M, Majtán J, Zeman M, Okuliarová M, Turčoková L, Knauer F. Covariation between eggshell colouration and eggshell bacteria abundance and egg characteristics in blackbirds. ETHOL ECOL EVOL 2019. [DOI: 10.1080/03949370.2019.1575910] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Herbert Hoi
- Department of Integrative Biology and Evolution, Konrad Lorenz Institute of Ethology, University of Veterinary Medicine, Savoyenstrasse 1a, 1160 Vienna, Austria
| | - Alžbeta Darolová
- Department of Animal Ecology, Institute of Zoology, Slovak Academy of Sciences, Dúbravská cesta 9, 845 06 Bratislava, Slovakia
| | - Ján Krištofík
- Department of Animal Ecology, Institute of Zoology, Slovak Academy of Sciences, Dúbravská cesta 9, 845 06 Bratislava, Slovakia
| | - Miroslav Poláček
- Department of Integrative Biology and Evolution, Konrad Lorenz Institute of Ethology, University of Veterinary Medicine, Savoyenstrasse 1a, 1160 Vienna, Austria
| | - Juraj Majtán
- Department of Microbiology, Institute of Molecular Biology, Slovak Academy of Sciences, Dúbravská cesta 9, 845 06 Bratislava, Slovakia
| | - Michal Zeman
- Department of Animal Physiology and Ethology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, 842 15 Bratislava, Slovakia
| | - Monika Okuliarová
- Department of Animal Physiology and Ethology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, 842 15 Bratislava, Slovakia
| | - Lucia Turčoková
- Department of Zoology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, 842 15 Bratislava, Slovakia
| | - Felix Knauer
- Department of Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine, Savoyenstrasse 1, 1160 Vienna, Austria
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Hasegawa M, Arai E, Nakamura M. Experimental manipulation of female tail length did not cause differential allocation by males in the barn swallow. Ethology 2017. [DOI: 10.1111/eth.12711] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Masaru Hasegawa
- Department of Evolutionary Studies of Biosystems; Sokendai (the Graduate University for Advanced Studies); Miura-gun Japan
| | - Emi Arai
- Department of Evolutionary Studies of Biosystems; Sokendai (the Graduate University for Advanced Studies); Miura-gun Japan
| | - Masahiko Nakamura
- Laboratory of Animal Ecology; Department of Biology; Joetsu University of Education; Joetsu-shi Japan
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Poláček M, Bartíková M, Hoi H. Intraclutch eggshell colour variation in birds: are females able to identify their eggs individually? PeerJ 2017; 5:e3707. [PMID: 28875071 PMCID: PMC5581944 DOI: 10.7717/peerj.3707] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Accepted: 07/28/2017] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND One possibility suggested regarding female post-mating strategies is differential allocation into offspring investment. Female birds produce not only the largest, but also most colourful eggs of all oviparous taxa. Larger eggs provide space for bigger embryos, or more nutrition for their development, but the question why eggs are more colourful and why there is variation in eggshell colouration remains. In this context, the focus of interest has been to explain inter-clutch variation but in many bird species, eggshell colouration also varies within a clutch. Surprisingly, less attention has been paid to this phenomenon. Therefore, we propose the "female egg recognition" hypothesis, suggesting that mothers use colour characteristics to interpret egg attributes and allocate further investment into each egg accordingly. To evaluate the feasibility of the hypothesis, we tested several underlying predictions and examined their suitability using a dataset from our tree sparrow (Passer montanus) study. We predict (i) substantial within-clutch variation in eggshell colouration which, (ii) should be related to laying sequence, (iii) reflect egg quality and, (iv) should stimulate a female response. METHODS Eggshell coloration data were obtained via digital photography under standardized conditions, taken after clutch completion. Lightness (L*), representing the achromatic properties of an egg has been chosen as the most important predictor in dark cavities and was related to egg quality and position in the nest. RESULTS In our tree sparrows, first and mainly last eggs were less pigmented, providing information about laying order. Egg volume, which predicts chick quality, positively correlates with eggshell coloration. Finally, we could show that female tree sparrows placed darker, but not bigger, eggs into more central incubation positions. DISCUSSION All basic prerequisites for the "female egg recognition" hypothesis are fulfilled. In this context practicability and feasibility of the hypothesis and alternative explanations are discussed. However future work is necessary to determine a direct effect on offspring condition.
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Affiliation(s)
- Miroslav Poláček
- Slovak Academy of Sciences, Institute of Zoology, Bratislava, Slovakia
- Konrad Lorenz Institute of Ethology, Department of Integrative Biology and Evolution, University of Veterinary Medicine, Vienna, Austria
| | - Michaela Bartíková
- Slovak Academy of Sciences, Institute of Zoology, Bratislava, Slovakia
- Konrad Lorenz Institute of Ethology, Department of Integrative Biology and Evolution, University of Veterinary Medicine, Vienna, Austria
| | - Herbert Hoi
- Konrad Lorenz Institute of Ethology, Department of Integrative Biology and Evolution, University of Veterinary Medicine, Vienna, Austria
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12
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Poláček M, Griggio M, Mikšík I, Bartíková M, Eckenfellner M, Hoi H. Eggshell coloration and its importance in postmating sexual selection. Ecol Evol 2017; 7:941-949. [PMID: 28168030 PMCID: PMC5288260 DOI: 10.1002/ece3.2664] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Revised: 10/26/2016] [Accepted: 10/31/2016] [Indexed: 11/12/2022] Open
Abstract
Avian eggshell color seems to fulfill multiple functions, some of them being structural and others signaling. In this study, we tested whether or not eggshell coloration may play a role in sexual selection of Tree Sparrows (Passer montanus). According to the "Sexually selected eggshell coloration" hypothesis, eggshell coloration signals female, egg or chick quality and males adjust parental investment according to this signal. Eggs of this species are covered with brown spots and patches, and variation between clutches is high. We found that eggshell coloration correlates with both protoporphyrin and biliverdin, but protoporphyrin concentrations are ten times higher. Eggshell coloration reflects egg and offspring quality, but not female quality. Thus, eggshell coloration may signal female postmating investment in offspring rather than female quality. Furthermore, differential allocation in terms of maternal investment is supported by the fact that females lay more pigmented clutches when mated to males with bigger melanin-based ornaments relative to their own. Moreover, males invested proportionally more to chicks that hatched from more pigmented clutches. Our correlative results thus seem to support a role of sexual selection in the evolution of eggshell coloration in birds laying brown eggs, pigmented mainly by protoporphyrin.
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Affiliation(s)
- Miroslav Poláček
- Institute of Zoology Slovak Academy of Sciences Bratislava Slovakia; Department of Integrative Biology and Evolution Konrad Lorenz Institute of Ethology University of Veterinary Medicine, Vienna Vienna Austria
| | - Matteo Griggio
- Department of Integrative Biology and Evolution Konrad Lorenz Institute of Ethology University of Veterinary Medicine, Vienna Vienna Austria; Department of Biology University of Padova Padova Italy
| | - Ivan Mikšík
- Department of Analytical Chemistry Faculty of Chemical Technology University of Pardubice Pardubice Czech Republic
| | - Michaela Bartíková
- Institute of Zoology Slovak Academy of Sciences Bratislava Slovakia; Department of Integrative Biology and Evolution Konrad Lorenz Institute of Ethology University of Veterinary Medicine, Vienna Vienna Austria
| | | | - Herbert Hoi
- Department of Integrative Biology and Evolution Konrad Lorenz Institute of Ethology University of Veterinary Medicine, Vienna Vienna Austria
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