scholarly journals Proximate Predictors of Variation in Egg Rejection Behavior by Hosts of Avian Brood Parasites

2019 ◽  
Author(s):  
Mikus Abolins-Abols ◽  
Mark E. Hauber
Keyword(s):  
Life History ◽  
Individual Variation ◽  
Physiological State ◽  
Adaptive Significance ◽  
Egg Rejection ◽  
Turdus Migratorius ◽  
American Robin ◽  
Brood Parasites ◽  
Rejection Probability ◽  
Explained Variation

AbstractThe rejection of parasitic eggs by hosts of avian brood parasites is one of the most common and effective defenses against parasitism. Despite its adaptive significance, egg rejection often shows substantial intraspecific variation: some individuals are more likely to remove or abandon parasitic eggs than others. Understanding variation in egg rejection requires that we study factors linked to both the ability to perceive parasitic eggs, as well as factors that may influence the rejection of a foreign egg once it has been recognized. Here we asked what cognitive, physiological, and life-history factors explained variation in the rejection of model eggs by American Robin Turdus migratorius females. We found that the probability of egg rejection was related to the clutch size at the time of parasitism: in support of Weber’s law, females with fewer eggs were more likely to reject the model eggs. In turn, females with greater mass and higher corticosterone levels were less likely to reject eggs, and egg rejection probability was negatively related to incubation progress. Our data thus suggest that proximate predictors of an individual’s egg rejection behavior include components of the nest’s perceptual environment, life-history factors, as well as the physiological state of the animal. However, much of the variation in the responses of robins to the model eggs remained unexplained. Future experiments should aim to understand the causal roles of these and other factors in generating within- and among-individual variation in the rejection of parasitic eggs.

scholarly journals Brood Parasitism Defense Behaviors Along an Altitudinal Gradient in the American Robin (Turdus Migratorius)

2016 ◽  
Vol 9 (1) ◽  
pp. 39-49 ◽  
Author(s):  
Lisa C. Carmody ◽  
Alexander Cruz ◽  
Jameson F. Chace
Keyword(s):  
Brood Parasitism ◽  
Nest Defense ◽  
Colorado Front Range ◽  
Egg Rejection ◽  
Front Range ◽  
Turdus Migratorius ◽  
Defense Behavior ◽  
American Robin ◽  
Brood Parasites ◽  
High Elevations

Some host species accept eggs from brood parasites over parts of their range and reject them in other areas representing an “evolutionary lag” in the development of rejection behavior or the loss of an adapative behavior when the selection pressure of brood parasitism is removed. Hosts may deter brood parasitism through egg rejection and aggressive nest defense behavior specifically targetting female brood parasites during the egg incubation period. In areas where parasitism frequencies are spatially and temporally variable, anti-parasite behaviors may decline as costs outweigh the benefits. Along the Colorado Front Range, American robins (Turdus migratorius) breed from low elevations where the brood parasitic Brown-headed Cowbird (Molothrus ater) is abundant to near timberline (3700 m) where cowbirds are uncommon. We tested the hypothesis that egg rejection and nest defense behaviors decline with reduced probability of parasitism. We found that robins accepted 100% of immaculate (robin-like) experimental eggs at both low and high elevations, but were more likely to reject spotted (cowbird-like) experimental eggs at low elevations than high elevations. Response to egg size was more variable than to egg color. When presented with a mount of a cowbird and Song Sparrow (Melospiza melodia) near the nest, robins responded more aggressively to cowbird models than to sparrows (control), and nest defense behavior towards cowbirds was longer and more aggressive at the lower elevation sites where cowbirds are common. These results suggest that egg rejection and nest-site aggression are costly adaptations to cowbird parasitism, and these behaviors decline when the threat of parasitism is reduced.

scholarly journals Ecophysiology of egg rejection in hosts of avian brood parasites: new insights and perspectives

2021 ◽  
Author(s):  
Francisco Ruiz-Raya
Keyword(s):  
Potential Role ◽  
Physiological State ◽  
Host Responses ◽  
Future Research ◽  
Egg Rejection ◽  
Fitness Costs ◽  
Brood Parasites ◽  
Proximate Mechanisms ◽  
Proximate Factors

Abstract Egg rejection is the most effective and widespread defence used by host species to counteract the extreme fitness costs frequently imposed by obligate avian brood parasites. Yet, the proximate mechanisms underlying between- and within-individual variation in host responses remain poorly explored. Emerging evidence suggests that egg rejection is dependent on individual physiological state, and draws attention to the role of hormones as mediators of flexible antiparasitic responses. In this perspective article, I outline recent advances in our understanding of the proximate factors that mediate egg rejection. I also point out some areas where knowledge remains still lacking, especially those related to the development and maintenance of effective cognitive functions, the potential role of oxidative stress, immunological state and developmental stressors. I propose new hypotheses that stimulate future research on behavioural host responses towards brood parasitism.

scholarly journals Natural and artificial scents do not increase egg rejection rates of model brood parasitic eggs by American robins (Turdus migratorius)

2020 ◽  
Vol 66 (4) ◽  
Author(s):  
Mark Erno Hauber
Keyword(s):  
Host Species ◽  
Molothrus Ater ◽  
Egg Rejection ◽  
Turdus Migratorius ◽  
Data Set ◽  
Brood Parasites ◽  
American Robins ◽  
Tactile Cues ◽  
Do So ◽  
Rejection Rates

Hosts of obligate avian brood parasites can diminish or eliminate the costs of parasitism by rejecting foreign eggs from the nests. A vast literature demonstrates that visual and/or tactile cues can be used to recognize and reject natural or model eggs from the nests of diverse host species. However, data on olfaction-based potential egg recognition cues are both sparse and equivocal: experimentally-applied, naturally-relevant (heterospecific, including parasitic) scents do not appear to increase egg rejection rates in two host species, whereas unnatural scents (human and tobacco scents) do so in one host species. Here I assessed the predictions that (i) human handling of mimetically-painted model eggs would increase rejection rates, and (ii) applying unnatural or natural scents to mimetically or non-mimetically painted model eggs alters these eggs’ respective rejection rates relative to controls. I studied wild American Robins (Turdus migratorius), a robust rejecter species of the eggs of obligate brood parasitic Brown-headed Cowbirds (Molothrus ater). There was no statistical evidence to support either prediction, whereas poorer color-mimicry was still a predicted cause of greater egg rejection in this data set. Nonetheless, future studies could focus on this and other host species and using these and different methods to apply and maintain the scenting of model eggs to more directly test hosts’ use of potential olfactory cues in the foreign-egg rejection process.

scholarly journals Glucocorticoids mediate egg rejection in a brood parasite host

2019 ◽  
Author(s):  
Mikus Abolins-Abols ◽  
Mark E. Hauber
Keyword(s):  
Causal Link ◽  
Host Responses ◽  
Egg Rejection ◽  
Brood Parasite ◽  
Ecological Significance ◽  
Turdus Migratorius ◽  
Free Living ◽  
Brood Parasites ◽  
American Robins ◽  
Host Behaviour

AbstractAvian brood parasites and their hosts are engaged in a coevolutionary battle that can result in the evolution of sophisticated trickery by parasites and novel defence behaviours in hosts. Despite the clear evolutionary and ecological significance of host behaviour, however, we know very little about the mechanisms that regulate host defences, which limits our understanding of both inter- and intraspecific variation in host responses to parasitism. Here we tested whether corticosterone, a hormone known to be upregulated in hosts exposed to parasitism, also mediates one of the most frequent host defences – the rejection of foreign eggs. We experimentally reduced corticosterone levels in free-living brood parasite hosts, American robins Turdus migratorius, using mitotane and found that the likelihood of model egg rejection was significantly lower in the mitotane-treated birds relative to the sham-treated birds. These results demonstrate a causal link between glucocorticoids and egg rejection in hosts of avian brood parasites, but the physiological and sensory-cognitive pathways that regulate this effect remain unknown.

High repeatability of egg rejection in response to experimental brood parasitism in the American robin (Turdus migratorius)

Behaviour ◽  
2014 ◽  
Vol 151 (6) ◽  
pp. 703-718 ◽  
Author(s):  
R. Croston ◽  
M.E. Hauber
Keyword(s):  
Brood Parasitism ◽  
Mixed Model ◽  
Linear Mixed Model ◽  
Generalized Linear Mixed Model ◽  
Presentation Order ◽  
Egg Rejection ◽  
Turdus Migratorius ◽  
American Robin ◽  
American Robins ◽  
High Repeatability

Repeatability is a measure of the amount of variation in a phenotype that is attributable to differences between individuals. This concept is important for any study of behaviour, as all traits of evolutionary interest must be repeatable in order to respond to selection. We investigated the repeatability of behavioural responses to experimental brood parasitism in American robins, a robust (100%) rejecter of parasitic brown-headed cowbird eggs. Because tests of repeatability require variation between individuals, we parasitized the same robin nests twice successively with model eggs dyed with colours known to elicit rejection at intermediate rates (58–70%). We calculated the repeatability of responses to parasitism, and used a generalized linear mixed model to also test for potentially confounding effects of ordinal date, presentation order, and clutch size. We found that repeatability in response to brood parasitism in this host species is high, and the best model predicting responses to sequential artificial parasitism includes only nest identity. This result is consistent with a critical assumption about egg rejection in this cowbird host as an evolved adaptation in response to brood parasitism.

scholarly journals The Perceptual and Cognitive Processes That Govern Egg Rejection in Hosts of Avian Brood Parasites

2021 ◽  
Vol 9 ◽  
Author(s):  
Daniel Hanley ◽  
Samantha L. Rutledge ◽  
Juliana Villa
Keyword(s):  
Cognitive Processing ◽  
Cognitive Processes ◽  
Selective Pressure ◽  
Null Model ◽  
Egg Rejection ◽  
Egg Recognition ◽  
Brood Parasites ◽  
The Past ◽  
The Cost ◽  
Receptor Noise

Hosts of avian brood parasites are under intense selective pressure to prevent or reduce the cost of parasitism. Many have evolved refined egg discrimination abilities, which can select for eggshell mimicry in their parasite. A classic assumption underlying these coevolutionary dynamics is that host egg recognition depends on the perceivable difference between their own eggs and those of their parasite. Over the past two decades, the receptor noise-limited (RNL) model has contributed to our understanding of these coevolutionary interactions by providing researchers a method to predict a host’s ability to discriminate a parasite’s egg from its own. Recent research has shown that some hosts are more likely to reject brown eggs than blue eggs, regardless of the perceived differences to their own. Such responses suggest that host egg recognition may be due to perceptual or cognitive processes not currently predictable by the RNL model. In this perspective, we discuss the potential value of using the RNL model as a null model to explore alternative perceptual processes and higher-order cognitive processes that could explain how and why some hosts make seemingly counter-intuitive decisions. Further, we outline experiments that should be fruitful for determining the perceptual and cognitive processing used by hosts for egg recognition tasks.

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