Egg ejection cost can limit defence strategies against brood parasitism

In coevolutionary arms races, like between cuckoos and their hosts, it is easy to understand why the host is under selection favouring anti-parasitism behaviour, such as egg rejection, which can lead to parasites evolving remarkable adaptations to ‘trick’ their host, such as mimetic eggs. But what about cases where the cuckoo egg is not mimetic and where the host does not act against it? Classically, such apparently non-adaptive behaviour is put down to evolutionary lag: given enough time, egg mimicry and parasite avoidance strategies will evolve. An alternative is that absence of egg mimicry and of anti-parasite behaviour is stable. Such stability is at first sight highly paradoxical. I show, using both field and experimental data to parametrize a simulation model, that the absence of defence behaviour by Cape bulbuls ( Pycnonotus capensis ) against parasitic eggs of the Jacobin cuckoo ( Clamator jacobinus ) is optimal behaviour. The cuckoo has evolved massive eggs (double the size of bulbul eggs) with thick shells, making it very hard or impossible for the host to eject the cuckoo egg. The host could still avoid brood parasitism by nest desertion. However, higher predation and parasitism risks later in the season makes desertion more costly than accepting the cuckoo egg, a strategy aided by the fact that many cuckoo eggs are incorrectly timed, so do not hatch in time and hence do not reduce host fitness to zero. Selection will therefore prevent the continuation of any coevolutionary arms race. Non-mimetic eggs and absence of defence strategies against cuckoo eggs will be the stable, if at first sight paradoxical, result.

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Creamy-Bellied Thrush Defenses Against Shiny Cowbird Brood Parasitism

The Condor ◽

10.1093/condor/107.4.788 ◽

2005 ◽

Vol 107 (4) ◽

pp. 788-796 ◽

Cited By ~ 3

Author(s):

Andrea A. Astie ◽

Juan C. Reboreda

Keyword(s):

Brood Parasitism ◽

Hatching Success ◽

Simultaneous Presentation ◽

Control Model ◽

Nest Attendance ◽

Chick Survival ◽

Molothrus Bonariensis ◽

Egg Ejection ◽

Cowbird Parasitism ◽

Recognition Errors

AbstractWe studied Creamy-bellied Thrush (Turdus amaurochalinus) defenses against brood parasitism by Shiny Cowbirds (Molothrus bonariensis). Shiny Cowbirds decrease the reproductive success of Creamy-bellied Thrushes, and having historical habitats and ranges that overlap, we expected that thrushes possess antiparasitic defenses. We analyzed nest attendance during prelaying, laying and incubation; responses to the presentation of a model of a female cowbird or a control species close to the nest; nest abandonment associated with parasitism; and responses to experimental parasitism with white or spotted cowbird eggs (with or without the simultaneous presentation of a female cowbird model). Nest attendance was 58%–68% during prelaying and 83%–90% during laying and incubation. Thrushes had a shorter latency in returning near the nest and visited nests more frequently when we presented the cowbird model than the control model. The frequency of abandonment of parasitized nests was low and was not temporally associated with parasitism. Thrushes ejected white eggs more frequently than spotted eggs when parasitism was associated with the presentation of the cowbird model, but there were no differences when the model was absent. Our results indicate that Creamy-bellied Thrushes recognize cowbirds as a threat and eject white but not spotted cowbird eggs. We postulate that the low impact of cowbird parasitism on thrush hatching success and chick survival and the likelihood of recognition errors when parasite eggs resemble host eggs may have prevented the evolution of egg ejection in this host.

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Experiments on egg discrimination in two North American corvids: further evidence for retention of egg ejection

Canadian Journal of Zoology ◽

10.1139/z04-118 ◽

2004 ◽

Vol 82 (9) ◽

pp. 1399-1407 ◽

Cited By ~ 17

Author(s):

Todd J Underwood ◽

Spencer G Sealy ◽

Celia M McLaren

Keyword(s):

Brood Parasitism ◽

Alternative Hypothesis ◽

Egg Discrimination ◽

Corvus Brachyrhynchos ◽

Detection Model ◽

Egg Ejection ◽

Significant Difference ◽

History Of ◽

Pica Nuttalli ◽

High Level

In the absence of brood parasitism in North America, black-billed magpies, Pica hudsonia (Sabine, 1822), and yellow-billed magpies, Pica nuttalli (Audubon, 1837), may have retained egg-discrimination behaviour that evolved in Eurasian magpies, Pica pica (L., 1758), in response to parasitism by Old World cuckoos. We further examined this hypothesis by testing the egg-discrimination abilities of black-billed magpies and the American crow, Corvus brachyrhynchos Brehm, 1822, which has no history of brood parasitism. In addition, we tested an alternative hypothesis that black-billed magpies evolved or retained egg discrimination to counter conspecific parasitism by testing their ability to eject foreign conspecific eggs and by using a signal detection model to estimate the level of conspecific parasitism required for ejection to be favoured. Black-billed magpies ejected all non-mimetic eggs and 62% of mimetic eggs. Significantly more mimetic eggs were ejected during the incubation stage than during the laying stage. Magpies ejected significantly more non-mimetic eggs than mimetic eggs overall, but there was no difference in ejection frequency during incubation. American crows ejected 21% of non-mimetic eggs and 8% of mimetic eggs. There was no significant difference in ejection frequency of the two egg types. Black-billed magpies ejected 11% of conspecific eggs and a relatively high level of conspecific parasitism (22%49%) would be required to select for conspecific ejection, which provides little support for conspecific parasitism as a current selection pressure for maintaining egg discrimination. Thus, black-billed magpies appear to have retained egg rejection in the absence of parasitism through speciation from Eurasian magpies.

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Discrimination and ejection of eggs and nestlings by the fan-tailed gerygone from New Caledonia

Current Zoology ◽

10.1093/cz/zoab066 ◽

2021 ◽

Author(s):

Alfredo Attisano ◽

Nozomu J Sato ◽

Keita Tanaka ◽

Yuji Okahisa ◽

Keisuke Ueda ◽

...

Keyword(s):

Breeding Season ◽

Brood Parasitism ◽

Visual Cues ◽

Size Range ◽

New Caledonia ◽

Host Defence ◽

Combined Approach ◽

Rare Type ◽

Egg Ejection ◽

Nestling Period

Abstract Nestling ejection is a rare type of host defence against brood parasitism compared to egg ejection. Theoretically, host defences at both egg and nestling stages could be based on similar underlying discrimination mechanisms but, due to the rarity of nestling ejector hosts, few studies have actually tested this hypothesis. We investigated egg and nestling discrimination by the fan-tailed gerygone Gerygone flavolateralis, a host that seemingly accepts non-mimetic eggs of its parasite, the shining bronze-cuckoo Chalcites lucidus, but ejects mimetic parasite nestlings. We introduced artificial eggs or nestlings and foreign gerygone nestlings in gerygone nests and compared begging calls of parasite and host nestlings. We found that the gerygone ejected artificial eggs only if their size was smaller than the parasite or host eggs. Ejection of artificial nestlings did not depend on whether their colour matched that of the brood. The frequency of ejection increased during the course of the breeding season mirroring the increase in ejection frequency of parasite nestlings by the host. Cross-fostered gerygone nestlings were frequently ejected when lacking natal down and when introduced in the nest before hatching of the foster brood, but only occasionally when they did not match the colour of the foster brood. Begging calls differed significantly between parasite and host nestlings throughout the nestling period. Our results suggest that the fan-tailed gerygone accepts eggs within the size range of gerygone or cuckoo eggs and that nestling discrimination is based on auditory and visual cues other than skin colour. This highlights the importance of using a combined approach to study discrimination mechanisms of hosts.

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Prolactin mediates behavioural rejection responses to avian brood parasitism

Journal of Experimental Biology ◽

10.1242/jeb.240101 ◽

2021 ◽

Author(s):

Francisco Ruiz-Raya ◽

Juan Diego Ibáñez-Álamo ◽

Charline Parenteau ◽

Olivier Chastel ◽

Manuel Soler

Keyword(s):

Brood Parasitism ◽

Positive Association ◽

Prolactin Secretion ◽

Host Responses ◽

Plasma Prolactin ◽

Physiological Mechanisms ◽

Parental Behaviour ◽

Brood Parasites ◽

Egg Ejection ◽

Avian Brood Parasitism

Adaptations resulting from co-evolutionary interactions between avian brood parasites and their hosts have been extensively studied, yet the physiological mechanisms underlying antiparasitic host defences remain little known. Prolactin, one of the main hormones involved in the regulation of avian parental behaviour, might play a key role in the orchestration of the host responses to avian brood parasitism. Given the positive association between prolactin and parental behaviour during incubation, decreasing prolactin levels are expected to facilitate egg-rejection decisions. We tested this prediction by implanting Eurasian blackbird (Turdus merula) females with an inhibitor of prolactin secretion, bromocriptine mesylate, to experimentally decrease their plasma prolactin levels. Bromocriptine-implanted individuals ejected mimetic model eggs at higher rates, and showed shorter latency to egg ejection, than placebo-treated birds. To our knowledge, this is the first experimental evidence that behavioural host defences against avian brood parasitism are mediated by prolactin.

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FIRST EVIDENCE OF CONSPECIFIC BROOD PARASITISM AND EGG EJECTION IN SONG SPARROWS, WITH COMMENTS ON METHODS SUFFICIENT TO DOCUMENT THESE

The Condor ◽

10.1650/0010-5422(2006)108[452:feocbp]2.0.co;2 ◽

2006 ◽

Vol 108 (2) ◽

pp. 452 ◽

Cited By ~ 7

Author(s):

Quresh S. Latif ◽

J. Letitia Grenier ◽

Sacha K. Heath ◽

Grant. Ballard ◽

Mark E. Hauber

Keyword(s):

Brood Parasitism ◽

Conspecific Brood Parasitism ◽

Egg Ejection ◽

Song Sparrows

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First Evidence of Conspecific Brood Parasitism and Egg Ejection in Song Sparrows, With Comments on Methods Sufficient to Document These

The Condor ◽

10.1093/condor/108.2.452 ◽

2006 ◽

Vol 108 (2) ◽

pp. 452-458

Author(s):

Quresh S. Latif ◽

J. Letitia Grenier ◽

Sacha K. Heath ◽

Grant Ballard ◽

Mark E. Hauber

Keyword(s):

Genetic Analysis ◽

Brood Parasitism ◽

Nest Predation ◽

Molothrus Ater ◽

Separate Study ◽

Conspecific Brood Parasitism ◽

Egg Ejection ◽

Song Sparrows ◽

Cowbird Parasitism ◽

Egg Marking

Abstract Conspecific brood parasitism occurs in many songbird species but has not been reported in Song Sparrows (Melospiza melodia). In three separate study areas where breeding Song Sparrows experience heavy nest predation pressure and Brown-headed Cowbird (Molothrus ater) parasitism, we observed six instances in which newly laid eggs were attributable to female Song Sparrows other than the nest owners. We also recorded the ejection of a sparrow egg from each of two videotaped nests. In a fourth study area without cowbird parasitism, genetic analysis of parentage revealed no conspecific brood parasitism. Given that egg ejection can accompany conspecific parasitism in Song Sparrows, we suggest that daily nest checks are insufficient to document the frequency of this tactic in some species in the absence of egg marking, videotaping, or genetic analyses. Since standard nest monitoring techniques may fail to detect conspecific brood parasitism, this behavior could be more prevalent than currently thought.

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