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Abolins‐Abols M, Peterson M, Studer B, Hale M, Hanley D, Bentley G, Hauber ME. Patterns of stress response to foreign eggs by a rejecter host of an obligate avian brood parasite. Ecol Evol 2023; 13:e9691. [PMID: 36699567 PMCID: PMC9848814 DOI: 10.1002/ece3.9691] [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: 05/26/2022] [Revised: 12/08/2022] [Accepted: 12/12/2022] [Indexed: 01/20/2023] Open
Abstract
One of the most effective defenses of avian hosts against obligate brood parasites is the ejection of parasitic eggs from the nests. Despite the clear fitness benefits of this behavior, individuals within so-called "egg-rejecter" host species still show substantial variation in their propensity to eliminate foreign eggs from the nest. We argue that this variation can be further understood by studying the physiological mechanisms of host responses to brood parasitic egg stimuli: independent lines of research increasingly support the hypothesis that stress-related physiological response to parasitic eggs may trigger egg rejection. The "stress-mediated egg rejection" hypothesis requires that hosts activate the stress-response when responding to parasitic egg stimuli. We tested this prediction by asking whether hosts showed differential stress response when exposed to host-like (mimetic) or parasite-like (non-mimetic) eggs. We experimentally parasitized incubating American robins Turdus migratorius, a robust egg-rejecter host to obligate brood parasitic brown-headed cowbirds Molothrus ater, with mimetic or non-mimetic model eggs. To assess the stress response, we measured the heart rate in incubating females immediately after experimental parasitism. We also measured plasma corticosterone and, in a subset of birds, used RNA-sequencing to analyze the expression of proopiomelanocortin (POMC), a precursor of adrenocorticotropic hormone, 2 h after experimental parasitism. We found that egg type had no effect on heart rate. Two hours following experimental parasitism, plasma corticosterone did not differ between the differently-colored model egg treatments or between rejecter and accepter females within the non-mimetic treatment. However, females exposed to non-mimetic eggs showed an upregulation of POMC gene expression (before FDR correction) in the pituitary compared with females treated with mimetic eggs. Our findings suggest that in an egg-rejecter host species, non-mimetic parasitic eggs may increase the activity of the stress-related hypothalamic-pituitary-adrenal axis compared with mimetic eggs, although the temporal dynamics of this response are not yet understood.
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Affiliation(s)
| | | | - Brett Studer
- Department of Evolution, Ecology, and Behavior, School of Integrative BiologyUniversity of Illinois at Urbana‐ChampaignUrbanaIllinoisUSA
| | - Mattison Hale
- Department of BiologyUniversity of LouisvilleLouisvilleKentuckyUSA
| | - Daniel Hanley
- Department of BiologyGeorge Mason UniversityFairfaxVirginiaUSA
| | - George Bentley
- Department of Integrative BiologyUniversity of California, BerkeleyBerkeleyCaliforniaUSA
| | - Mark E. Hauber
- Department of Evolution, Ecology, and Behavior, School of Integrative BiologyUniversity of Illinois at Urbana‐ChampaignUrbanaIllinoisUSA
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Turner AM, Di Giovanni AJ, Antonson ND, Scharf HM, Abolins-Abols M, Hauber ME. Non-invasive elevation of circulating corticosterone increases the rejection of foreign eggs in female American robins (Turdus migratorius). Horm Behav 2022; 146:105278. [PMID: 36395578 DOI: 10.1016/j.yhbeh.2022.105278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2022] [Revised: 10/10/2022] [Accepted: 10/31/2022] [Indexed: 11/16/2022]
Abstract
Avian obligate brood parasites rely on other species to raise their offspring. In turn, many brood parasite hosts have evolved defensive behaviors to reduce the costs of brood parasitism, yet the proximate bases underlying these defenses remain poorly understood. Recent studies regarding the potential endocrine mechanisms of foreign-egg rejection have implicated corticosterone as a physiological mediator of anti-parasitic defenses. For example, corticosterone is elevated in response to non-mimetic eggs in an egg rejecter thrush, the Eurasian blackbird (Turdus merula) and this hormone's suppression reduces egg rejection rates in the congeneric American robin (T. migratorius). American robins are also among the few host species of obligate brood parasitic brown-headed cowbirds (Molothrus ater) that readily reject foreign eggs from their nests. We non-invasively elevated corticosterone levels in incubating female robins by dissolving it in DMSO gel which was then applied onto eggs already in the clutch. Relative to controls treated with pure DMSO gel, corticosterone-treated female robins were more likely to reject a non-mimetic, cowbird-sized foreign egg (72 %) than control females (50 %) when accounting for the known effect of lower clutch sizes on greater egg rejection. Future studies are needed to assess the sensory and cognitive impact(s) of corticosterone, as well as other hormones essential for parental care, in this and other hosts' defense behaviors against avian brood parasitism.
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Affiliation(s)
- Abbigail M Turner
- Deparment of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, IL, 61801, USA.
| | - Alexander J Di Giovanni
- Deparment of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, IL, 61801, USA
| | - Nicholas D Antonson
- Deparment of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, IL, 61801, USA
| | - Hannah M Scharf
- Deparment of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, IL, 61801, USA
| | | | - Mark E Hauber
- Deparment of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, IL, 61801, USA
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Turner AM, Di Giovanni AJ, Hoover JP, Hauber ME. Eggshell texture but not odor treatment affects model egg rejection in American robins (Turdus migratorius). Anim Cogn 2022; 25:1307-1312. [PMID: 35325327 DOI: 10.1007/s10071-022-01614-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 02/15/2022] [Accepted: 03/12/2022] [Indexed: 11/01/2022]
Abstract
To curb fitness costs associated with obligate avian brood parasitism, some hosts have evolved to reject foreign eggs in the nest. American robins (Turdus migratorius) are among the few hosts of the brown-headed cowbird (Molothrus ater) that mostly remove parasitic eggs from their nests. With the parasite's eggs looking nothing like their own, American robins likely rely most on visual cues when making rejection decisions. However, we still know little about the roles that tactile and olfactory cues play in robin's or other rejecter hosts' rejection decisions. Here, we conducted a set of experiments to test for the use of tactile or olfactory cues in egg rejection by robins. For the tactile experiment, we found that robins were more likely to reject rough rather than smooth eggs. However, our tactile model egg design was not able to fully discriminate between tactile and visual sensory modalities. In the olfaction experiment, we did not find a significant effect of egg scent treatment on rejection rates. Accordingly, future studies on egg rejection should attempt to fully distinguish between tactile and visual cues, as well as examine olfactory cues in other egg rejecter host species.
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Affiliation(s)
- Abbigail M Turner
- Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
| | - Alexander J Di Giovanni
- Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Jeffrey P Hoover
- Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Urbana, IL, 61820, USA
| | - Mark E Hauber
- Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.,Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Urbana, IL, 61820, USA
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Hauber ME, Winnicki SK, Hoover JP, Hanley D, Hays IR. The limits of egg recognition: testing acceptance thresholds of American robins in response to decreasingly egg-shaped objects in the nest. ROYAL SOCIETY OPEN SCIENCE 2021; 8:201615. [PMID: 33614093 PMCID: PMC7890492 DOI: 10.1098/rsos.201615] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 01/06/2021] [Indexed: 05/28/2023]
Abstract
Some hosts of avian brood parasites reduce or eliminate the costs of parasitism by removing foreign eggs from the nest (rejecter hosts). In turn, even acceptor hosts typically remove most non-egg-shaped objects from the nest, including broken shells, fallen leaves and other detritus. In search for the evolutionary origins and sensory mechanisms of egg rejection, we assessed where the potential threshold between egg recognition and nest hygiene may lie when it comes to stimulus shape. Most previous studies applied comparisons of egg-sized objects with non-continuous variation in shape. Here, instead, we used two series of three-dimensional-printed objects, designed a priori to increasingly diverge from natural eggs along two axes (width or angularity) of shape variation. As predicted, we detected transitions from mostly acceptance to mostly rejection in the nests of American robins Turdus migratorius along each of the two axes. Our methods parallel previous innovations in egg-rejection studies through the use of continuous variation in egg coloration and maculation contrast, to better understand the sensory limits and thresholds of variation in egg recognition and rejection in diverse hosts of avian brood parasites.
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Affiliation(s)
- Mark E. Hauber
- Department of Evolution, Ecology, and Behavior, University of Illinois at Urbana-Champaign, Urbana, IL, USA
- Program in Ecology, Evolution, and Conservation, University of Illinois at Urbana-Champaign, Urbana, IL, USA
- Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Sarah K. Winnicki
- Department of Evolution, Ecology, and Behavior, University of Illinois at Urbana-Champaign, Urbana, IL, USA
- Program in Ecology, Evolution, and Conservation, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Jeffrey P. Hoover
- Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Daniel Hanley
- Department of Biology, George Mason University, Fairfax, VA, USA
| | - Ian R. Hays
- Department of Biological Sciences; Rutgers, The State University of New Jersey, Newark, NJ, USA
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