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.

scholarly journals Endocrine regulation of egg rejection in an avian brood parasite host

2020 ◽  
Vol 16 (6) ◽  
pp. 20200225 ◽  
Author(s):  
Mikus Abolins-Abols ◽  
Mark E. Hauber
Keyword(s):  
Stress Response ◽  
Stress Physiology ◽  
Endocrine Regulation ◽  
Egg Rejection ◽  
Brood Parasite ◽  
Potential Mechanism ◽  
Turdus Migratorius ◽  
American Robins ◽  
Defence Behaviour ◽  
Behavioural Adaptations

Parasite–host coevolution can lead to novel behavioural adaptations in hosts to resist parasitism. In avian obligate brood parasite and host systems, many host species have evolved diverse cognitive and behavioural traits to recognize and reject parasitic eggs. Our understanding of the evolution and ecology of these defences hinges on identifying the mechanisms that regulate them. We hypothesized that corticosterone, a hormone linked to stress response, vigilance and the suppression of parental behaviour, stimulates the rejection of foreign eggs by brood parasite hosts. We experimentally reduced circulating glucocorticoid levels with mitotane injections in American robins Turdus migratorius and found that the mitotane-treated birds rejected foreign eggs at a lower frequency compared to the sham-treated subjects. This is the first study to causally identify a potential mechanism of a widespread defence behaviour, and it is consistent with egg rejection being mediated by stress physiology.

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 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 Mimicry-dependent lateralization in the visual inspection of foreign eggs by American robins

2019 ◽  
Vol 15 (7) ◽  
pp. 20190351 ◽  
Author(s):  
Hannah M. Scharf ◽  
Katharine Stenstrom ◽  
Miri Dainson ◽  
Thomas J. Benson ◽  
Esteban Fernandez-Juricic ◽  
...  
Keyword(s):  
Visual Processing ◽  
Species Recognition ◽  
Molothrus Ater ◽  
Population Level ◽  
Brain Lateralization ◽  
Turdus Migratorius ◽  
Brain Hemispheres ◽  
Brood Parasites ◽  
Visual Hemifield ◽  
American Robins

Brain lateralization, or the specialization of function in the left versus right brain hemispheres, has been found in a variety of lineages in contexts ranging from foraging to social and sexual behaviours, including the recognition of conspecific social partners. Here we studied whether the recognition and rejection of avian brood parasitic eggs, another context for species recognition, may also involve lateralized visual processing. We focused on American robins ( Turdus migratorius ), an egg-rejecter host to occasional brood parasitism by brown-headed cowbirds ( Molothrus ater ) and tested if robins preferentially used one visual hemifield over the other to inspect mimetic versus non-mimetic model eggs. At the population level, robins showed a significantly lateralized absolute eyedness index (EI) when viewing mimetic model eggs, but individuals varied in left versus right visual hemifield preference. By contrast, absolute EI was significantly lower when viewing non-mimetic eggs. We also found that robins with more lateralized eye usage rejected model eggs at higher rates. We suggest that the inspection and recognition of foreign eggs represent a specialized and lateralized context of species recognition in this and perhaps in other egg-rejecter hosts of brood parasites.

Clutch variation and egg rejection in three hosts of the pallid cuckoo, Cuculus pallidus

Behaviour ◽  
2010 ◽  
Vol 147 (1) ◽  
pp. 19-36 ◽  
Author(s):  
Naomi Langmore ◽  
Michelle Landstrom ◽  
Robert Heinsohn
Keyword(s):  
Host Species ◽  
Rejection Rate ◽  
Objective Measures ◽  
Egg Rejection ◽  
Brood Parasite ◽  
Reflectance Spectrophotometry ◽  
Brood Parasites ◽  
Parasitised Host

AbstractIn theory, hosts of avian brood parasites would benefit by modifying their egg appearance in two ways to help identify mimetic foreign eggs: (i) by laying clutches that are more uniform in appearance and (ii) by laying clutches that differ from those of other females in the population. Support for these theories is inconsistent, and few studies have used objective measures of clutch variation. Here we used reflectance spectrophotometry to quantify within-clutch and between-clutch variation of three host species of an Australian brood parasite, the pallid cuckoo (Cuculus pallidus). We used egg-swapping experiments in which subjects were presented with either a conspecific egg or a heterospecific egg to compare the egg rejection responses of a frequently parasitised host, the white-plumed honeyeater (Lichenostomus penicillatus), with two less frequently parasitised hosts, dusky woodswallows (Artamus cyanopterus) and willie wagtails (Rhipidura leucophrys). As predicted, rejection rate increased as contrast between foreign egg and host clutch increased. Further, the major host showed greater between-clutch variation than the occasional hosts, and also rejected more similar-looking eggs. Contrary to predictions however, within-clutch variation was not lower in the major host, nor was it important in predicting the rejection rate of foreign eggs by the three host species.

scholarly journals The Evolution of Predator Resemblance in Avian Brood Parasites

2021 ◽  
Vol 9 ◽  
Author(s):  
Jennifer E. York
Keyword(s):  
Cognitive Processes ◽  
Signal Detection Theory ◽  
Natural Variation ◽  
Host Responses ◽  
Brood Parasite ◽  
Brood Parasites ◽  
Physiological Processes ◽  
Prey Behavior ◽  
The Common ◽  
Independent Effects

Predators have profound effects on prey behavior and some adult brood parasites use predator resemblance to exploit the antipredator defenses of their hosts. Clarifying host perception of such stimuli is important for understanding the adaptive significance of adult brood parasite characteristics, and the mechanisms by which they misdirect hosts. Here I review the literature to explore the adaptive basis of predator resemblance in avian brood parasites, and natural variation in host responses to these stimuli. I also provide a framework for the information ecology of predator resemblance, which is based on the principles of signal detection theory and draws from empirical evidence from the common cuckoo, Cuculus canorus, as the most widely studied system. In this species, visual and acoustic hawk-like stimuli are effective in manipulating host defenses. Overall, contrasts across host responses suggest that different modalities of information can have independent effects on hosts, and that predator resemblance takes advantage of multiple sensory and cognitive processes. Host perception of these stimuli and the degree to which they are processed in an integrated manner, and the physiological processes underlying regulation of the responses, present new avenues for brood parasitism research.

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 Shared transcriptional responses to con- and heterospecific behavioral antagonists in a wild songbird

2019 ◽  
Author(s):  
Matthew I. M. Louder ◽  
Michael Lafayette ◽  
Amber A. Louder ◽  
Floria M. K. Uy ◽  
Christopher N. Balakrishnan ◽  
...  
Keyword(s):  
Behavioral Plasticity ◽  
Molothrus Ater ◽  
System Response ◽  
Brood Parasite ◽  
Functional Responses ◽  
Transcriptional Responses ◽  
Free Living ◽  
Brood Parasites ◽  
Singing Behavior ◽  
Immune System Response

AbstractThe recognition of and differential responses to salient stimuli are among the main drivers of behavioral plasticity, yet, how animals evolve and modulate functional responses to novel classes of antagonistic stimuli remain poorly understood. We studied free-living male red-winged blackbirds (Agelaius phoeniceus) to test whether gene expression responses in blood are distinct or shared between patterns of aggressive behavioral responses directed at simulated conspecific versus heterospecific intruders. In this species, males defend territories against conspecific males and respond aggressively to female brown-headed cowbirds (Molothrus ater), a brood parasite that commonly lays eggs in blackbird nests. Both conspecific songs and parasitic calls elicited aggressive responses from focal subjects and caused a downregulation in genes associated with immune system response, relative to control calls of a second, harmless heterospecific species. In turn, only the conspecific song treatment elicited an increase in singing behavior and an upregulation of genes associated with metabolic processes relative to the two heterospecific calls. Our results suggest that aspects of antagonistic responses to both conspecifics and brood parasites can be based on similar physiological responses, suggestive of shared molecular and behavioral pathways involved in the recognition and reaction to both evolutionarily old and new enemies.

scholarly journals Visual acuity and egg spatial chromatic contrast predict egg rejection behavior of American robins

2020 ◽  
Vol 223 (20) ◽  
pp. jeb229609
Author(s):  
Alec B. Luro ◽  
Esteban Fernández-Juricic ◽  
Patrice Baumhardt ◽  
Mark E. Hauber
Keyword(s):  
Visual Acuity ◽  
Host Species ◽  
Spatial Vision ◽  
Viewing Distance ◽  
Egg Rejection ◽  
Chromatic Contrast ◽  
Brood Parasites ◽  
American Robins ◽  
Avian Visual System ◽  
The Cost

ABSTRACTColor and spatial vision is critical for recognition and discrimination tasks affecting fitness, including finding food and mates, and recognizing offspring. For example, as a counter defense to avoid the cost of raising the unrelated offspring of obligate interspecific avian brood parasites, many host species routinely view, recognize and remove the foreign egg(s) from their nests. Recent research has shown that host species visually attend to both chromatic and spatial pattern features of eggs; yet how hosts simultaneously integrate these features together when recognizing eggs remains an open question. Here, we tested egg rejection responses of American robins (Turdus migratorius) using a range of 3D-printed model eggs covered with blue and yellow checkered patterns differing in relative square sizes. We predicted that robins would reject a model egg if they could visually resolve the blue and yellow squares as separate features, or accept it if the squares blended together and appeared similar in color to the natural blue–green color of robin eggs as perceived by the avian visual system. As predicted, the probability of robins rejecting a model egg increased with greater sizes of its blue and yellow squares. Our results suggest that chromatic visual acuity and viewing distance have the potential to limit the ability of a bird to recognize a foreign egg in its nest, thus providing a limitation to host egg recognition that obligate interspecific avian brood parasites may exploit.

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