Absence Of Brood Parasitism Research Articles

Egg rejection in blackbirds Turdus merula: a by-product of conspecific parasitism or successful resistance against interspecific brood parasites?

BackgroundTraditional theory assumes that egg recognition and rejection abilities arise as a response against interspecific brood parasitism (IBP). However, rejection also appears in some species that are currently not exploited by interspecific parasites, such as Turdus thrushes. Recent evidences suggest that rejection abilities evolved in these species as a response to conspecific brood parasitism (CBP). To test these two alternative hypotheses, we performed an experimental study by parasitizing nests of the common blackbird (Turdus merula) with conspecifics or heterospecific eggs under different risk of parasitism (presence of interspecific or conspecific parasites near the nest). Common blackbird is a potential host of the common cuckoo (Cuculus canorus) but suffers low levels of CBP too.ResultsWe found that blackbirds were able to recognize and eject heterospecific eggs at high rates whereas most of conspecifics eggs were not recognized and, therefore, accepted. Ejection rates of conspecific eggs did not exceed 13 %, even in situations of high risk of CBP (blackbird female placed near the nest), which contradict the main prediction derived from the CBP hypothesis. Conversely, ejection rates of experimental eggs simulating IBP were much higher (80–100 %). Furthermore, female blackbirds were more aggressive towards cuckoos than towards blackbird dummies.ConclusionsOur results considered together support the IBP hypothesis, indicating that recognition and rejection of parasitic eggs in blackbirds have probably evolved due to previous cuckoo parasitism. The current absence of IBP in blackbirds may be due to the highly efficient rejection abilities in this species. Thus, these abilities have been retained in absence of brood parasitism as a consequence of the low costs involved for blackbirds, resulting in a successful resistance against interspecific brood parasitism.

Yellow warbler defenses are retained in the absence of brood parasitism but enhanced by experience with cowbirds

Yellow warblers, Setophaga petechia, respond to brood parasitic brown-headed cowbirds, Molothrus ater, by giving alarm calls and rushing to protect their nests. These responses are typically given in populations sympatric with cowbirds, but rarely in allopatric populations. Whether the lower expression in allopatry has a genetic basis or instead could be explained by behavioral plasticity has not been investigated. We found that warblers exposed to cowbirds in Montana (sympatric) responded significantly more often to cowbird models with seet calls (85.7%) and nest protection behavior (80.0%) than conspecifics breeding in long-term isolation from cowbirds in Alaska (allopatric, 27.3% and 16.7%, respectively). Warblers breeding in Idaho, which were locally isolated from cowbirds (naive) but presumed to be genetically similar to nearby parasitized warblers, were significantly less likely than sympatric warblers to respond to cowbird models with seet calls (30.3%) and nest protection (17.3%). The lower responsiveness of naive warblers implies behavioral plasticity in trait expression, indicating that the lower responsiveness of allopatric warblers relative to sympatric warblers could be explained entirely by plasticity. The lower expression of these defenses in the absence of cowbirds may contribute to their persistence by minimizing potentially costly recognition errors.

Egg color variation, but not egg rejection behavior, changes in a cuckoo host breeding in the absence of brood parasitism.

Interactions between parasitic cuckoos and their songbird hosts form a classical reciprocal “arms race,” and are an excellent model for understanding the process of coevolution. Changes in host egg coloration via the evolution of interclutch variation in egg color or intraclutch consistency in egg color are hypothesized counter adaptations that facilitate egg recognition and thus limit brood parasitism. Whether these antiparasitism strategies are maintained when the selective pressure of parasitism is relaxed remains debated. However, introduced species provide unique opportunities for testing the direction and extent of natural selection on phenotypic trait maintenance and variation. Here, we investigated egg rejection behavior and egg color polymorphism in the red-billed leiothrix (Leiothrix lutea), a common cuckoo (Cuculus canorus) host, in a population introduced to Hawaii 100 years ago (breeding without cuckoos) and a native population in China (breeding with cuckoos). We found that egg rejection ability was equally strong in both the native and the introduced populations, but levels of interclutch variation and intraclutch consistency in egg color in the native population were higher than in the introduced population. This suggests that egg rejection behavior in hosts can be maintained in the absence of brood parasitism and that egg appearance is maintained by natural selection as a counter adaptation to brood parasitism. This study provides rare evidence that host antiparasitism strategies can change under parasite-relaxed conditions and reduced selection pressure.

Defence behaviour against brood parasitism is deeply rooted in mainland and island scrub-jays

When selection pressures for an adaptation relax, the trait may decline, or it may be maintained if there are no fitness costs. The interactions between avian brood parasites and their hosts are dynamic, with selection pressures changing as host or parasite ranges shift, or as parasites switch to new hosts once old hosts evolve defences. The extent to which hosts retain defences in the absence of parasites has important consequences to parasite–host coevolution. We tested whether island scrub-jays, Aphelocoma insularis , and western scrub-jays, A. californica , have maintained egg ejection behaviour in the absence of brood parasitism and provide an estimate of how long they have maintained ejection. Island scrub-jays and western scrub-jays ejected 100% of foreign eggs placed into their nests, and genetic analyses revealed no evidence of conspecific brood parasitism that could maintain ejection. Extreme variation in intraclutch egg appearance may result in hosts ejecting their own oddly coloured eggs, which would select against the maintenance of ejection. However, island, western and Florida scrub-jays, A. coerulescens , also an ejecter, showed less variation than the common grackle, Quiscalus quiscula , a species that has an extremely high level of intraclutch egg variation and may have lost its rejection defence, because it rejects its own oddly coloured eggs. Based on molecular clock analyses of mitochondrial DNA control region and ND2 sequences, island and western scrub-jays split approximately 140 000–151 000 years ago, western and Florida scrub-jays 1 000 000 years ago, and island and Florida scrub-jays 1 250 000 years ago. Ejection behaviour may have been maintained this long in the absence of parasitism, but it is possible that scrub-jays were parasitized as recently as the end of the Pleistocene 10 000 years ago, when cowbirds were more abundant. Nevertheless, these results indicate that (1) egg ejection is not a costly trait to maintain in scrub-jays, (2) brood parasites may not be able to alternate between well-defended hosts and hosts that have lost ejection defence following past episodes of parasitism and (3) brood parasites may have to deal with host communities that have well-developed defences by evolving specialized adaptations for a single host species or a small set of species.

Fate of Grackle (Quiscalus SPP.) Defenses in the Absence of Brood Parasitism: Implications for Long-Term Parasite-Host Coevolution

Abstract We tested grackles (Quiscalus spp.) to determine whether they retain egg rejection behavior in the absence of the selection pressure of brood parasitism. Neither Bronzed Cowbird (Molothrus aeneus) nor Brown-headed Cowbird (M. ater) parasitism was recorded in 797 Great-tailed Grackle (Q. mexicanus) nests. Cross-fostered Bronzed Cowbird nestlings, but not Brown-headed Cowbird nestlings, fledged from Great-tailed Grackle nests, indicating that Brown-headed Cowbird parasitism does not select for rejection in these grackles. Great-tailed Grackle populations sympatric and allopatric with Bronzed Cowbirds rejected 100% of model cowbird eggs. An allopatric population of Boat-tailed Grackle (Q. major), a sister species of the Great-tailed Grackle, also rejected 100% of model eggs. Egg rejection in the Boat-tailed Grackle has apparently been retained in the absence of parasitism for as long as 800,000 years since it split from the Great-tailed Grackle. The Common Grackle (Q. quiscula), which lays the most variable eggs among the grackles, also has the lowest level of egg rejection—which is consistent with the argument that it may have lost most of its rejection behavior in the absence of parasitism. With extreme intraclutch egg-variation, Common Grackles may be more likely to reject their own oddly colored eggs, which would select against rejection behavior in the absence of parasitism. Those results have significant implications for long-term parasite-host coevolution, because they suggest that egg rejection has been retained in most species of Quiscalus in the absence of parasitism. If typical of the world's avifauna, such retention may force brood parasites to specialize on a few host species and to rarely return to using old hosts, which would readily reject their eggs.

Fate of Grackle (Quiscalus spp.) Defenses in the Absence of Brood Parasitism: Implications for Long-Term Parasite-Host Coevolution

Fate of Grackle (Quiscalus spp.) Defenses in the Absence of Brood Parasitism: Implications for Long-Term Parasite-Host Coevolution

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

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.

Egg rejection by Iberian azure‐winged magpiesCyanopica cyanusin the absence of brood parasitism

The Iberian azure‐winged magpieCyanopica cyanusshows a remarkable ability to discriminate against great spotted cuckooClamator glandariuseggs. Here, I studied whether egg recognition in this species could be a derived feature resulting from intra‐specific brood parasitism. Azure‐winged magpies showed a very high level of discrimination and rejection of great spotted cuckoo models (73.7%), and of conspecific eggs (42.8%), even when no evidence of great spotted cuckoo or conspecific brood parasitism has been found in the population. Azure‐winged magpie discriminated more readily than magpies, the current favourite host of the great spotted cuckoo. The high rejection rate of conspecific eggs by the azure‐winged magpie suggests that it is quite possible that egg discrimination in this species evolved in response to conspecific brood parasitism rather than to cuckoo parasitism.

Intraspecific Brood Parasitism in Two Tit Parus species: Occurrence and Responses to Experimental Parasitism

In many bird species females parasitize the parental investment of other pairs by laying eggs in their nests. Such intraspecific brood parasitism is considered rare among altricial birds, but this may result from methodological difficulties in detecting and quantifying this behaviour. In this study, we investigated first whether intraspecific brood parasitism occurs in Blue Tits Parus caeruleus and Great Tits P. major, using a combination of frequent nest inspections, DNA profiling and a survey of the literature. No evidence for parasitism was found. Next, we investigated whether the absence of brood parasitism could be explained by efficient anti-parasite strategies of the hosts. We experimentally parasitized 75 Blue Tit and 51 Great Tit nests before and during egg-laying. We found no evidence for rejection of the parasitic eggs. Thus the absence of brood parasitism is not a product of undetected parasitism. Although intense female-female aggression may deter females that try to lay eggs in other nests, we suggest that in both species intraspecific brood parasitism has not evolved because females do not benefit from laying eggs in the nests of others.

Desertion of nests parasitized by cowbirds: have clay-coloured sparrows evolved an anti-parasite defence?

Abstract. Clay-coloured sparrows, Spizella pallida, have often been reported deserting nests parasitized by brown-headed cowbirds, Molothrus ater. Sparrow nests were experimentally parasitized and manipulated to determine whether desertion is an anti-parasite defence. Responses to experimental parasitism with and without the presence of a cowbird model, the addition of broken eggs to the nest, changes in clutch composition (combination of sparrow and cowbird eggs), clutch reductions, and human nest visitation were recorded. Only clutch reduction elicited nest desertion. Because such reductions can occur in the absence of brood parasitism, desertion apparently has not evolved as an anti-parasite defence in this species. Desertion of naturally parasitized nests appears to be a response to host egg removal by female cowbirds, rather than to parasitism per se. The absence of anti-parasite defences in clay-coloured sparrows is not adequately explained by the equilibrium hypothesis and, contrary to an earlier suggestion, clay-coloured sparrows are not in transition between being an acceptor and rejector species of cowbird parasitism. More attention needs to be paid to the host egg removal aspect of cowbird parasitism.