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1.
In the arms race between avian brood parasites and their hosts, several adaptations and counter‐adaptations have evolved. The most prominent host defence is rejection of parasitic eggs. We experimentally parasitized nests of 10 potential host species breeding in sympatry with four different cuckoo species in an area in Bangladesh using differently coloured model eggs to test host responses. In four species we introduced both mimetic and non‐mimetic eggs. Black Drongos Dicrurus macrocercus, hosts of the Indian Cuckoo Cuculus micropterus, rejected all model eggs. Common Mynas Acridotheres tristis and Jungle Babblers Turdoides striata accepted all eggs regardless of mimicry. These two species are parasitized by Asian Koels Eudynamys scolopaceus, Common Hawk‐cuckoo Hierococcyx varius and, in the case of Jungle Babblers, Jacobin Cuckoos Clamator jacobinus. Pied Mynas Gracupica contra, with no records of parasitism in our study area, also accepted all eggs regardless of mimicry. In the six remaining species, all of which lay spotted eggs, we introduced only non‐mimetic eggs. Black‐hooded Orioles Oriolus xanthornus rejected all model eggs, even though we have found no records of natural parasitism. Long‐tailed Shrikes Lanius schach and House Crows Corvus splendens, hosts of Asian Koels, rejected 75 and 9.1% of model eggs, respectively. Large‐billed Crows Corvus macrorhynchos, apparently not used as hosts in our study area, accepted all blue but rejected all brown model eggs. Oriental Magpie‐Robins Copsychus saularis and Red‐vented Bulbuls Pycnonotus cafer accepted all non‐mimetic model eggs. In Black Drongos, Long‐tailed Shrikes and Black‐hooded Orioles, all model eggs were ejected within 24 h of introduction. The results show considerable variation in egg rejection rates among various species, providing baseline data for further investigation of co‐evolutionary interactions between brood parasites and hosts in this region.  相似文献   

2.
The evolution of egg rejection by cuckoo hosts in Australia and Europe   总被引:4,自引:0,他引:4  
Exploitation of hosts by brood parasitic cuckoos is expectedto stimulate a coevolutionary arms race of adaptations and counteradaptations.However, some hosts have not evolved defenses against parasitism.One hypothesis to explain a lack of host defenses is that thelife-history strategies of some hosts reduce the cost of parasitismto the extent that accepting parasitic eggs in the nest is evolutionarilystable. Under this hypothesis, it pays hosts to accept cuckooeggs if (1) the energetic cost of raising the cuckoo is low,(2) there is time to renest, and (3) clutch size is small. Weparasitized the nests of host and nonhost species with nonmimeticmodel eggs to test whether the evolution of egg recognitionby cuckoo hosts could be explained by life-history variablesof the host. The most significant factor explaining rates ofrejection of model eggs was whether or not a species was a cuckoohost, with hosts rejecting model eggs at a higher rate thannonhosts. Egg-rejection rates were also explained by visibilitywithin the nest and by cuckoo mass. We found little supportfor the life-history model of egg rejection. Our results suggestthat parasitism is always sufficiently costly to select forhost defenses and that the evolution of defenses may be limitedby proximate constraints such as visibility within the nest.  相似文献   

3.
Obligate avian brood parasitism typically involves one of 2strategies: parasite chicks are either 1) virulent and evictall other eggs and nest mates to be raised alone or 2) moretolerant and share foster parental care with host chicks forsome or the entirety of the nestling period. We studied theconsequences of experimentally forced mixed broods of age-matchedone common cuckoo (Cuculus canorus) and 2 great reed warbler(Acrocephalus arundinaceus) chicks. In these broods, both cuckooand host chicks grew slower than did either individual cuckoosor great reed warblers in broods of 1 parasite or 3 host chicks,respectively. Video records showed that in mixed broods, cuckoochicks received feedings less frequently than the 33% predictedby chance at 4 days of age but parental food allocations increasedto chance levels at 8 days of age. The consistent patterns oflower growth rates arose even though chicks in broods of 1 parasiteand 2 hosts received the largest prey items per feeding. Inaddition, several other measures of parental provisioning alsodid not predict species and brood-specific differences in nestlinggrowth rates across the different treatments. However, variationin begging displays and its specific costs on host and parasitechicks in the different nest treatments were not quantifiedin this study. We conclude that young of nest mate–evictorcommon cuckoos benefit from the sole occupancy of host nestsin part owing to an initial competitive disadvantage for parentalcare in broods with age-matched great reed warbler chicks.  相似文献   

4.
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.  相似文献   

5.
In this article we present tentative support for predictionsderived from a spatial habitat structure hypothesis arguingthat common cuckoos Cuculus canorus, the most common obligatebrood parasite in Europe, only breed in areas where they haveaccess to vantage points in trees. Thus, species in which somepopulations breed near trees while other populations breed farther from trees have a different cuckoo—host population dynamicthan species in which all populations always breed in the vicinityof trees. Parasitism rate, mimicry of brood parasite eggs withthose of the hosts, and rejection behavior of hosts varieswith the host breeding habitat. Cuckoos are best adapted toexploit species in which some populations breed near trees while other populations breed in open areas because such hosts arenot always accessible to cuckoos, and thus gene flow amongunparasitized and parasitized populations delays the evolutionof host adaptations. Adaptive behavior in cuckoos as well asin their hosts can be predicted from the spatial habitat structurehypothesis.  相似文献   

6.
Garamszegi LZ  Avilés JM 《Oecologia》2005,143(1):167-177
Interspecific brood parasites may use the secondary sexual characters of the hosts to decide which species to parasitize. Hence, species with conspicuous and well-recognisable traits may have higher chances of becoming parasitised. Using North American birds and their frequent brood parasite, the brown-headed cowbird Molothrus ater, we tested the relationship between features of song and plumage coloration of hosts and the frequency of brood parasitism while controlling for several potentially confounding factors. Relying on two sets of analysis, we focused separately on the evolutionary view of the parasite and the host. From the cowbirds perspective, we found that males of heavily parasitized species posit songs with low syllable repertoire size, shorter inter-song interval and have brighter plumage. From the hosts perspective, a phylogenetic analysis revealed similar associations for features of song, but not for plumage characteristics that were unrelated to brood parasitism. These comparative findings may imply that brood parasites choose novel hosts based on heterospecific signals; and/or host species working against sexual selection escape from brood parasitism by evolving inconspicuous sexual signals. Although our data do not allow us to distinguish between these two evolutionary scenarios, our results suggest that selection factors mediating cowbird parasitism via host recognition by heterospecific signals may have an important role in the evolutionary relationship between brood parasites and their hosts.Electronic Supplementary Material Supplementary material is available for this article at  相似文献   

7.
Brood parasitic birds impose variable fitness costs upon their hosts by causing the partial or complete loss of the hosts' own brood. Growing evidence from multiple avian host-parasite taxa indicates that exposure of individual hosts to parasitism is not necessarily random and varies with habitat use, nest-site selection, age or other phenotypic attributes. For instance, nonrandom patterns of brood parasitism had similar evolutionary consequences to those of limited horizontal transmission of parasites and pathogens across space and time and altered the dynamics of both population productivity and co-evolutionary interactions of hosts and parasites. We report that brood parasitism status of hosts of brown-headed cowbirds Molothrus ater is also transmitted across generations in individually colour-banded female prothonotary warblers Protonotaria citrea. Warbler daughters were more likely to share their mothers' parasitism status when showing natal philopatry at the scale of habitat patch. Females never bred in their natal nestboxes but daughters of parasitized mothers had shorter natal dispersal distances than daughters of nonparasitized mothers. Daughters of parasitized mothers were more likely to use nestboxes that had been parasitized by cowbirds in both the previous and current years. Although difficult to document in avian systems, different propensities of vertical transmission of parasitism status within host lineages will have critical implications both for the evolution of parasite tolerance in hosts and, if found to be mediated by lineages of parasites themselves, for the difference in virulence between such extremes as the nestmate-tolerant and nestmate-eliminator strategies of different avian brood parasite species.  相似文献   

8.
Passerine hosts of parasitic cuckoos usually vary in their abilityto discriminate and reject cuckoo eggs. Costs of discriminationand rejection errors have been invoked to explain the maintenanceof this within-population variability. Recently, enforcementof acceptance by parasites has been identified as a rejectioncost in the magpie (Pica pica) and its brood parasite, the greatspotted cuckoo (Clamator glandarius). Previous experimentalwork has shown that rejecter magpies suffer from increased nestpredation by the great spotted cuckoo. Cuckoo predatory behavioris supposed to confer a selective advantage to the parasitebecause magpies experiencing a reproductive failure may providea second opportunity for the cuckoo to parasitize a replacementclutch. This hypothesis implicitly assumes that magpies modulatetheir propensity to reject parasite eggs as a function of previousexperience. We tested this hypothesis in a magpie populationbreeding in study plots varying in parasitism rate. Magpie pairs thatwere experimentally parasitized and had their nests depredated,after their rejection behavior had been assessed, changed theirbehavior from rejection to acceptance. The change in host behaviorwas prominent in study plots with high levels of parasitism,but not in plots with rare or no cuckoo parasitism. We discussthree possible explanations for these differences, concludingthat in study plots with a high density of cuckoos, the probability fora rejecter magpie nest of being revisited and depredated bya cuckoo is high, particularly for replacement clutches, and,therefore, the cost for magpies of rejecting a cuckoo egg ina replacement clutch is increased. Moreover, in areas with highlevels of host defense (low parasitism rate), the probabilityof parasitism and predation of rejecter-magpie nests by thecuckoo is reduced in both first and replacement clutches. Therefore,rejecter magpies in such areas should not change their rejectionbehavior in replacement clutches.  相似文献   

9.
Parasite-mediated selection is potentially of great importance in modulating genetic diversity. Genetic variation for resistance, the fuel for natural selection, appears to be common in host-parasite interactions, but responses to selection are rarely observed. In the present study, we tested whether environmental variation could mediate infection and determine evolutionary outcomes. Temperature was shown to dramatically alter the potential for parasite-mediated selection in two independent laboratory infection experiments at four temperatures. The bacterial parasite, Pasteuria ramosa, was extremely virulent at 20 degrees C and 25 degrees C, sterilizing its host, Daphnia magna, so that females often never produced a single brood. However, at 10 degrees C and 15 degrees C, the host-parasite interaction was much more benign, as nearly all females produced broods before becoming sterile. This association between virulence and temperature alone could stabilize coexistence and lead to the maintenance of diversity, because it would weaken parasite-mediated selection during parts of the season. Additionally, highly significant genotype-by-environment interactions were found, with changes in clone rank order for infection rates at different temperatures. Our results clearly show that the outcome of parasite-mediated selection in this system is strongly context dependent.  相似文献   

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