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Intraspecific brood parasitism can increase the number of eggs that an individual lays in its own nest.

ABSTRACT: Intraspecific brood parasitism involves laying eggs in the nest of another individual of the same species without subsequently caring for the eggs or hatchlings. Where individuals lay in their own nest as well as parasitically, previous works predicted that parasitism leads to fewer eggs being laid in an individual's own nest, compared with the equivalent situation without parasitism. This is predicted to occur both to reduce the effects of competition from parasitically laid individuals and because parasitism can be used to reduce competition between siblings. Here, we present a quantitative model of this situation. This model indicates that the brood-reduction prediction does not hold universally. For some plausible parameter combinations, parasitism causes an increase rather than a decrease in the number of eggs laid by an individual in its own nest. This occurs because parasitism becomes a less profitable tactic as more eggs are laid by nest owners due to increasing within-nest competition. Increasing clutch size will also increase competition between the host's own offspring, but can still be advantageous if the induced reduction in parasitism is sufficient.

SUBMITTER: Ruxton GD

PROVIDER: S-EPMC1691123 | biostudies-literature | 2002 Oct

REPOSITORIES: biostudies-literature

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Intraspecific brood parasitism can increase the number of eggs that an individual lays in its own nest.

Ruxton Graeme D GD Broom Mark M

Proceedings. Biological sciences 20021001 1504

Intraspecific brood parasitism involves laying eggs in the nest of another individual of the same species without subsequently caring for the eggs or hatchlings. Where individuals lay in their own nest as well as parasitically, previous works predicted that parasitism leads to fewer eggs being laid in an individual's own nest, compared with the equivalent situation without parasitism. This is predicted to occur both to reduce the effects of competition from parasitically laid individuals and bec ...[more]

PMID: 12396497

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Project description:Selective pressures imposed by pathogenic microorganisms to embryos have selected in hosts for a battery of antimicrobial lines of defenses that includes physical and chemical barriers. Due to the antimicrobial properties of volatile compounds of green plants and of chemicals of feather degrading bacteria, the use of aromatic plants and feathers for nest building has been suggested as one of these barriers. However, experimental evidence suggesting such effects is scarce in the literature. During two consecutive years, we explored experimentally the effects of these nest materials on loads of different groups of bacteria (mesophilic bacteria, Enterobacteriaceae, Staphylococcus and Enterococcus) of eggshells in nests of spotless starlings (Sturnus unicolor) at the beginning and at the end of the incubation period. This was also explored in artificial nests without incubation activity. We also experimentally increased bacterial density of eggs in natural and artificial nests and explored the effects of nest lining treatments on eggshell bacterial load. Support for the hypothetical antimicrobial function of nest materials was mainly detected for the year and location with larger average values of eggshell bacterial density. The beneficial effects of feathers and plants were more easily detected in artificial nests with no incubation activity, suggesting an active role of incubation against bacterial colonization of eggshells. Pigmented and unpigmented feathers reduced eggshell bacterial load in starling nests and artificial nest boxes. Results from artificial nests allowed us to discuss and discard alternative scenarios explaining the detected association, particularly those related to the possible sexual role of feathers and aromatic plants in starling nests. All these results considered together confirm the antimicrobial functionality mainly of feathers but also of plants used as nest materials, and highlight the importance of temporally and geographically environmental variation associated with risk of bacterial proliferation determining the strength of such effects. Because of costs associated to nest building, birds should adjust nest building effort to expected bacterial environments during incubation, a prediction that should be further explored.

Project description:BackgroundWhy have birds evolved the ability to reject eggs? Typically, foreign egg discrimination is interpreted as evidence that interspecific brood parasitism (IP) has selected for the host's ability to recognize and eliminate foreign eggs. Fewer studies explore the alternative hypothesis that rejection of interspecific eggs is a by-product of host defenses, evolved against conspecific parasitism (CP). We performed a large scale study with replication across taxa (two congeneric Turdus thrushes), space (populations), time (breeding seasons), and treatments (three types of experimental eggs), using a consistent design of egg rejection experiments (n?=?1057 nests; including controls), in areas with potential IP either present (Europe; native populations) or absent (New Zealand; introduced populations). These comparisons benefited from the known length of allopatry (one and a half centuries), with no gene flow between native and introduced populations, which is rarely available in host-parasite systems.ResultsHosts rejected CP at unusually high rates for passerines (up to 60%). CP rejection rates were higher in populations with higher conspecific breeding densities and no risks of IP, supporting the CP hypothesis. IP rejection rates did not covary geographically with IP risk, contradicting the IP hypothesis. High egg rejection rates were maintained in the relatively long-term isolation from IP despite non-trivial rejection costs and errors.ConclusionsThese egg rejection patterns, combined with recent findings that these thrushes are currently unsuitable hosts of the obligate parasitic common cuckoo (Cuculus canorus), are in agreement with the hypothesis that the rejection of IP is a by-product of fine-tuned egg discrimination evolved due to CP. Our study highlights the importance of considering both IP and CP simultaneously as potential drivers in the evolution of egg discrimination, and illustrates how populations introduced to novel ecological contexts can provide critical insights into brood parasite-host coevolution.

Dataset Information

Intraspecific brood parasitism can increase the number of eggs that an individual lays in its own nest.

Publications

Intraspecific brood parasitism can increase the number of eggs that an individual lays in its own nest.

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