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Di Giovanni AJ, Villa J, Stanback MT, Thompson CF, Sakaluk SK, Hauber ME, Hanley D. Decision rules for egg-color-based rejection by two cavity-nesting hosts of the brown-headed cowbird. J Exp Biol 2023; 226:jeb245188. [PMID: 37357579 PMCID: PMC10399979 DOI: 10.1242/jeb.245188] [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: 10/13/2022] [Accepted: 06/21/2023] [Indexed: 06/27/2023]
Abstract
Hosts of obligate avian brood parasites often evolve defense mechanisms to avoid rearing unrelated young. One common defense is egg rejection, for which hosts often rely on eggshell color. Most research has assumed that hosts respond to perceived color differences between their own eggs and parasite eggs regardless of the particular color; however, recent experiments have found that many hosts respond more strongly to brown foreign eggs than to equally dissimilar blue eggs. Yet, none of these prior studies tested a brown-egg-laying species and, with only one exception, all were conducted in open nests where light levels are considered sufficient for effective color-based egg discrimination. Here, we explored how two cavity-nesting hosts of the parasitic brown-headed cowbird (Molothrus ater) - the blue-egg-laying eastern bluebird (Sialia sialis) and the brown-egg-laying house wren (Troglodytes aedon) - respond to experimental eggs painted six distinct colors ranging from blue to brown. Rejection responses of both hosts were best predicted by perceived differences in color between the model egg and their own eggs. Specifically, we found that house wrens preferentially rejected eggs bluer than their own eggs. However, although we found that bluebirds relied on perceived differences in color for their egg rejection decisions, further tests are needed to determine whether they preferentially rejected brown eggs or simply responded to absolute perceived differences in color. These findings demonstrate that these cavity-nesting birds treat perceived color differences in distinct ways, which has important implications on the coevolutionary arms races and the interpretation of avian-perceived color differences.
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Affiliation(s)
| | - Juliana Villa
- Department of Biology, George Mason University, Fairfax, VA 22030, USA
| | - Mark T. Stanback
- Department of Biology, Davidson College, Davidson, NC 28035, USA
| | - Charles F. Thompson
- Behavior, Ecology, Evolution, and Conservation Section, School of Biological Sciences, Illinois State University, Normal, IL 61790, USA
| | - Scott K. Sakaluk
- Behavior, Ecology, Evolution, and Conservation Section, School of Biological Sciences, Illinois State University, Normal, IL 61790, USA
| | - Mark E. Hauber
- Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| | - Daniel Hanley
- Department of Biology, George Mason University, Fairfax, VA 22030, USA
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Schmitz Ornés A, Ducay RL, Fulmer AG, Hauber ME. Coloniality and development impact intraclutch consistency of avian eggs: a comparative analysis of the individual repeatability of eggshell size and shape metrics. THE SCIENCE OF NATURE - NATURWISSENSCHAFTEN 2023; 110:12. [PMID: 36943536 DOI: 10.1007/s00114-023-01840-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 02/19/2023] [Accepted: 02/21/2023] [Indexed: 03/23/2023]
Abstract
In oviparous animals, egg morphology is considered an aspect of the extended phenotype of the laying mother and, thus, can be directly assessed for consistency both within and between individual females. Despite a recently renewed interest in the evolution and mechanics of avian eggshell morphology, we still lack a large-scale, comparative understanding of which egg traits are individually plastic and whether individual consistency is shaped by ecological and life history traits at the species level. Here, we aimed to understand whether intraclutch repeatability per se of different eggshell metrics is an evolving trait that responds to selection pressures from socio-ecological contexts across a diverse group of avian species for which clutch-level eggshell morphology data were available to us. Coloniality, ontogeny, and incubation period had significant impacts on the comparative patterns of relative individual repeatability among two egg metrics (i.e., size and shape), whereas other life history traits (including adult size, clutch size, nest type, migration, breeding latitude, host status of brood parasitism) did not have statistical impacts. Our results also demonstrate that individual consistency has a more widespread phylogenetic distribution than expected by evolutionary contingency across avian diversity. Future analyses should also incorporate the effects of intra- and interspecific covariation in other morphological and physiological traits on the evolution of individual consistency, especially those relevant to egg recognition, including eggshell color and maculation.
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Affiliation(s)
- Angela Schmitz Ornés
- AG Vogelwarte, Zoological Institute and Museum, University of Greifswald, 17489, Greifswald, Germany
| | - Rebecca L Ducay
- Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- School of Forestry and Horticulture, Southern Illinois University, Carbondale, IL, 62901, USA
| | - Andrew G Fulmer
- Department of Psychology, Fort Lewis College, Durango, CO, 81301, USA
| | - Mark E Hauber
- Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
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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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McClelland SC, Cassey P, Maurer G, Hauber ME, Portugal SJ. How much calcium to shell out? Eggshell calcium carbonate content is greater in birds with thinner shells, larger clutches and longer lifespans. J R Soc Interface 2021; 18:20210502. [PMID: 34583563 PMCID: PMC8479367 DOI: 10.1098/rsif.2021.0502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 09/07/2021] [Indexed: 11/17/2022] Open
Abstract
The avian eggshell is a bio-ceramic structure that protects the embryo. It is composed almost entirely of calcium carbonate and a small amount of organic material. An optimal amount of calcium carbonate in the eggshell is essential for the embryo's development, yet how the ratio of calcium carbonate to organic matter varies between species has not been investigated. Calcium is a limiting resource for most birds, so its investment in their eggs should be optimized for a bird's life history. We measured the relative calcium carbonate content of eggshells in 222 bird species and tested hypotheses for how this trait has evolved with the life-history strategies of these species and other traits of their respective egg physiologies. We found that (i) eggshell calcium carbonate content was positively correlated with species having thinner eggshells and smaller than expected eggs relative to incubating parental mass, (ii) species with small mean clutch sizes had lower calcium carbonate content in their eggshells, and (iii) for species with larger clutch sizes, eggshell calcium carbonate content was negatively correlated with their mean lifespan. The pattern of lower eggshell calcium carbonate in longer lived, larger clutched birds suggests that calcium provision to the eggshell has long-term costs for the individual.
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Affiliation(s)
- Stephanie C. McClelland
- Department of Biological Sciences, School of Life and Environmental Sciences, Royal Holloway University of London, Egham TW20 0EX, UK
| | - Phillip Cassey
- Invasion Science & Wildlife Ecology Lab, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Golo Maurer
- BirdLife Australia, 2/5, 60 Leicester Street, Carlton, Victoria 3053, Australia
- Centre for Tropical Environmental and Sustainability Studies, College of Science and Engineering, James Cook University, Cairns, Queensland 4878, Australia
| | - Mark E. Hauber
- Department of Evolution, Ecology, and Behavior, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Steven J. Portugal
- Department of Biological Sciences, School of Life and Environmental Sciences, Royal Holloway University of London, Egham TW20 0EX, UK
- The Natural History Museum, Tring HP23 6AP, UK
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