Social interactions modulate the virulence of avian malaria infection

There is an increasing understanding of the context-dependent nature of parasite virulence. Variation in parasite virulence can occur when infected individuals compete with conspecifics that vary in infection status; virulence may be higher when competing with uninfected competitors. In vertebrates with social hierarchies, we propose that these competition-mediated costs of infection may also vary with social status. Dominant individuals have greater competitive ability than competing subordinates, and consequently may pay a lower prevalence-mediated cost of infection. In this study we investigated whether costs of malarial infection were affected by the occurrence of the parasite in competitors and social status in domestic canaries (Serinus canaria). We predicted that infected subordinates competing with non-infected dominants would pay higher costs than infected subordinates competing with infected dominants. We also predicted that these occurrence-mediated costs of infection would be ameliorated in infected dominant birds. We found that social status and the occurrence of parasites in competitors significantly interacted to change haematocrit in infected birds. Namely, subordinate and dominant infected birds differed in haematocrit depending on the infection status of their competitors. However, in contrast to our prediction, dominants fared better with infected subordinates, whereas subordinates fared better with uninfected dominants. Moreover, we found additional effects of parasite occurrence on mortality in canaries. Ultimately, we provide evidence for costs of parasitism mediated by social rank and the occurrence of parasites in competitors in a vertebrate species. This has important implications for our understanding of the evolutionary processes that shape parasite virulence and group living

Females tend to prefer genetically similar mates in an island population of house sparrows

BACKGROUND: It is often proposed that females should select genetically dissimilar mates to maximize offspring genetic diversity and avoid inbreeding. Several recent studies have provided mixed evidence, however, and in some instances females seem to prefer genetically similar males. A preference for genetically similar mates can be adaptive if outbreeding depression is more harmful than inbreeding depression or if females gain inclusive fitness benefits by mating with close kin. Here, we investigated genetic compatibility and mating patterns in an insular population of house sparrow (Passer domesticus), over a three-year period, using 12 microsatellite markers and one major histocompability complex (MHC) class I gene. Given the small population size and the distance from the mainland, we expected a reduced gene flow in this insular population and we predicted that females would show mating preferences for genetically dissimilar mates. RESULTS: Contrary to our expectation, we found that offspring were less genetically diverse (multi-locus heterozygosity) than expected under a random mating, suggesting that females tended to mate with genetically similar males. We found high levels of extra-pair paternity, and offspring sired by extra-pair males had a better fledging success than those sired by the social male. Again, unexpectedly, females tended to be more closely related to extra-pair mates than to their social mates. Our results did not depend on the type of genetic marker used, since microsatellites and MHC genes provided similar results, and we found only little evidence for MHC-dependent mating patterns. CONCLUSIONS: These results are in agreement with the idea that mating with genetically similar mates can either avoid the disruption of co-adapted genes or confer a benefit in terms of kin selection

Evolutionary ecology of avian malaria : experimental approaches of the relationships between Plasmodium relictum and domestic canary

L'étude des interactions hôtes/parasites est actuellement un thème de recherche incontournable des sciences de l'évolution. Une des questions majeures soulevée par ces études est de comprendre pourquoi certains parasites provoquent des maladies mortelles, alors que d'autres restent relativement bénins pour leurs hôtes. Dans ce défi que tentent de relever les biologistes de l’évolution mais également les sciences médicales, nous avons choisi de nous intéresser à la malaria aviaire, et plus précisément à son représentant le plus commun dans les populations naturelles d’oiseaux : Plasmodium relictum. En procédant à des infections expérimentales de canaris domestiques (Serinus canaria), nous avons voulu comprendre quels facteurs liés aux caractéristiques du parasite et de l’oiseau (au niveau de l’individu ou de la population) pouvaient influencer la virulence de Plasmodium relictum. Nous avons ainsi pu mettre en évidence que des facteurs, tels que le passé infectieux de l’hôte, la dose de parasites reçue, la prévalence de ces derniers dans la population d’oiseaux ou bien encore les interactions sociales entre individus, pouvaient moduler les coûts d’une telle infection. La virulence est un trait composite qui dépend, certes, de l’exploitation de l’hôte par les parasites mais également de la réponse immunitaire de ce dernier contre l’infection. Nous avons pu le vérifier dans notre système expérimental en utilisant une approche immuno-écologique. Nous nous sommes enfin intéressée aux conditions favorisant l’évolution de la virulence : ce qui est essentiel pour comprendre l’émergence ou la réémergence de maladies infectieuses et pour développer des stratégies de contrôle de ces maladies.Host-parasite interaction became one of the main topics of evolutionary sciences researches. One of the major issues raised by these studies is to understand why some parasites cause fatal diseases while others remain relatively mild to their hosts. In this challenge attempting to take up the evolutionary biologist and the medical sciences, we focused on avian malaria, and more specifically on its most common parasite: Plasmodium relictum. In performing experimental infections in domestic canaries (Serinus canaria), we wanted to understand what factors related to parasite and birds characteristics, could influence Plasmodium relictum virulence. We highlighted that factors such as infectious past, parasites dose, prevalence in bird’s population and social interactions between individuals could modulate costs of such infection. Virulence is a composite trait that depends on the host’s exploitation by parasites but also the host’s immune response against the infection. We were able to show that in our experimental system using an approach of immunological ecology. Finally we focused on the conditions favouring the virulence evolution: an essential point to understand emergence or re-emergence of infectious diseases and to develop strategies to control these diseases

Ecologie évolutive de la malaria aviaire : approches expérimentales des relations entre Plasmodium relictum et le canari domestique

Host-parasite interaction became one of the main topics of evolutionary sciences researches. One of the major issues raised by these studies is to understand why some parasites cause fatal diseases while others remain relatively mild to their hosts. In this challenge attempting to take up the evolutionary biologist and the medical sciences, we focused on avian malaria, and more specifically on its most common parasite: Plasmodium relictum. In performing experimental infections in domestic canaries (Serinus canaria), we wanted to understand what factors related to parasite and birds characteristics, could influence Plasmodium relictum virulence. We highlighted that factors such as infectious past, parasites dose, prevalence in bird’s population and social interactions between individuals could modulate costs of such infection. Virulence is a composite trait that depends on the host’s exploitation by parasites but also the host’s immune response against the infection. We were able to show that in our experimental system using an approach of immunological ecology. Finally we focused on the conditions favouring the virulence evolution: an essential point to understand emergence or re-emergence of infectious diseases and to develop strategies to control these diseases.L'étude des interactions hôtes/parasites est actuellement un thème de recherche incontournable des sciences de l'évolution. Une des questions majeures soulevée par ces études est de comprendre pourquoi certains parasites provoquent des maladies mortelles, alors que d'autres restent relativement bénins pour leurs hôtes. Dans ce défi que tentent de relever les biologistes de l’évolution mais également les sciences médicales, nous avons choisi de nous intéresser à la malaria aviaire, et plus précisément à son représentant le plus commun dans les populations naturelles d’oiseaux : Plasmodium relictum. En procédant à des infections expérimentales de canaris domestiques (Serinus canaria), nous avons voulu comprendre quels facteurs liés aux caractéristiques du parasite et de l’oiseau (au niveau de l’individu ou de la population) pouvaient influencer la virulence de Plasmodium relictum. Nous avons ainsi pu mettre en évidence que des facteurs, tels que le passé infectieux de l’hôte, la dose de parasites reçue, la prévalence de ces derniers dans la population d’oiseaux ou bien encore les interactions sociales entre individus, pouvaient moduler les coûts d’une telle infection. La virulence est un trait composite qui dépend, certes, de l’exploitation de l’hôte par les parasites mais également de la réponse immunitaire de ce dernier contre l’infection. Nous avons pu le vérifier dans notre système expérimental en utilisant une approche immuno-écologique. Nous nous sommes enfin intéressée aux conditions favorisant l’évolution de la virulence : ce qui est essentiel pour comprendre l’émergence ou la réémergence de maladies infectieuses et pour développer des stratégies de contrôle de ces maladies

Ecologie évolutive de la malaria aviaire (approches expérimentales des relations entre Plasmodium relictum et le canari domestique)

L'étude des interactions hôtes/parasites est actuellement un thème de recherche incontournable des sciences de l'évolution. Une des questions majeures soulevée par ces études est de comprendre pourquoi certains parasites provoquent des maladies mortelles, alors que d'autres restent relativement bénins pour leurs hôtes. Dans ce défi que tentent de relever les biologistes de l évolution mais également les sciences médicales, nous avons choisi de nous intéresser à la malaria aviaire, et plus précisément à son représentant le plus commun dans les populations naturelles d oiseaux : Plasmodium relictum. En procédant à des infections expérimentales de canaris domestiques (Serinus canaria), nous avons voulu comprendre quels facteurs liés aux caractéristiques du parasite et de l oiseau (au niveau de l individu ou de la population) pouvaient influencer la virulence de Plasmodium relictum. Nous avons ainsi pu mettre en évidence que des facteurs, tels que le passé infectieux de l hôte, la dose de parasites reçue, la prévalence de ces derniers dans la population d oiseaux ou bien encore les interactions sociales entre individus, pouvaient moduler les coûts d une telle infection. La virulence est un trait composite qui dépend, certes, de l exploitation de l hôte par les parasites mais également de la réponse immunitaire de ce dernier contre l infection. Nous avons pu le vérifier dans notre système expérimental en utilisant une approche immuno-écologique. Nous nous sommes enfin intéressée aux conditions favorisant l évolution de la virulence : ce qui est essentiel pour comprendre l émergence ou la réémergence de maladies infectieuses et pour développer des stratégies de contrôle de ces maladies.Host-parasite interaction became one of the main topics of evolutionary sciences researches. One of the major issues raised by these studies is to understand why some parasites cause fatal diseases while others remain relatively mild to their hosts. In this challenge attempting to take up the evolutionary biologist and the medical sciences, we focused on avian malaria, and more specifically on its most common parasite: Plasmodium relictum. In performing experimental infections in domestic canaries (Serinus canaria), we wanted to understand what factors related to parasite and birds characteristics, could influence Plasmodium relictum virulence. We highlighted that factors such as infectious past, parasites dose, prevalence in bird s population and social interactions between individuals could modulate costs of such infection. Virulence is a composite trait that depends on the host s exploitation by parasites but also the host s immune response against the infection. We were able to show that in our experimental system using an approach of immunological ecology. Finally we focused on the conditions favouring the virulence evolution: an essential point to understand emergence or re-emergence of infectious diseases and to develop strategies to control these diseases.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Effect of repeated exposure to Plasmodium relictum (lineage SGS1) on infection dynamics in domestic canaries.

7 pagesInternational audienceParasites are known to exert strong selection pressures on their hosts and, as such, favour the evolution of defence mechanisms. The negative impact of parasites on their host can have substantial consequences in terms of population persistence and the epidemiology of the infection. In natural populations, however, it is difficult to assess the cost of infection while controlling for other potentially confounding factors. For instance, individuals are repeatedly exposed to a variety of parasite strains, some of which can elicit immunological memory, further protecting the host from subsequent infections. Cost of infection is, therefore, expected to be particularly strong for primary infections and to decrease for individuals surviving the first infectious episode that are re-exposed to the pathogen. We tested this hypothesis experimentally using avian malaria parasites (Plasmodium relictum-lineage SGS1) and domestic canaries (Serinus canaria) as a model. Hosts were infected with a controlled dose of P. relictum as a primary infection and control birds were injected with non-infected blood. The changes in haematocrit and body mass were monitored during a 20 day period. A protein of the acute phase response (haptoglobin) was assessed as a marker of the inflammatory response mounted in response to the infection. Parasite intensity was also monitored. Surviving birds were then re-infected 37 days post primary infection. In agreement with the predictions, we found that primary infected birds paid a substantially higher cost in terms of infection-induced reduction in haematocrit compared with re-exposed birds. After the secondary infection, re-exposed hosts were also able to clear the infection at a faster rate than after the primary infection. These results have potential consequences for the epidemiology of avian malaria, since birds re-exposed to the pathogen can maintain parasitemia with low fitness costs, allowing the persistence of the pathogen within the host population

Le moineau domestique à Hoedic, biologie des populations insulaires.

8 pagesNational audienc

Social interactions modulate the virulence of avian malaria infection

There is an increasing understanding of the context-dependent nature of parasite virulence. Variation in parasite virulence can occur when infected individuals compete with conspecifics that vary in infection status; virulence may be higher when competing with uninfected competitors. In vertebrates with social hierarchies, we propose that these competition-mediated costs of infection may also vary with social status. Dominant individuals have greater competitive ability than competing subordinates, and consequently may pay a lower prevalence-mediated cost of infection. In this study we investigated whether costs of malarial infection were affected by the occurrence of the parasite in competitors and social status in domestic canaries (Serinus canaria). We predicted that infected subordinates competing with non-infected dominants would pay higher costs than infected subordinates competing with infected dominants. We also predicted that these occurrence-mediated costs of infection would be ameliorated in infected dominant birds. We found that social status and the occurrence of parasites in competitors significantly interacted to change haematocrit in infected birds. Namely, subordinate and dominant infected birds differed in haematocrit depending on the infection status of their competitors. However, in contrast to our prediction, dominants fared better with infected subordinates, whereas subordinates fared better with uninfected dominants. Moreover, we found additional effects of parasite occurrence on mortality in canaries. Ultimately, we provide evidence for costs of parasitism mediated by social rank and the occurrence of parasites in competitors in a vertebrate species. This has important implications for our understanding of the evolutionary processes that shape parasite virulence and group living. © 2013 Australian Society for Parasitology Inc.Financial support was provided by the Région Bourgogne (France), the CNRS (France; Programme MIE) and the ANR (IRMAL) (France). http://dx.doi.org/10.1016/j.ijpara.2013.05.008Peer Reviewe

Social interactions modulate the virulence of avian malaria infection

There is an increasing understanding of the context-dependent nature of parasite virulence. Variation in parasite virulence can occur when infected individuals compete with conspecifics that vary in infection status; virulence may be higher when competing with uninfected competitors. In vertebrates with social hierarchies, we propose that these competition-mediated costs of infection may also vary with social status. Dominant individuals have greater competitive ability than competing subordinates, and consequently may pay a lower prevalence-mediated cost of infection. In this study we investigated whether costs of malarial infection were affected by the occurrence of the parasite in competitors and social status in domestic canaries (Serinus canaria). We predicted that infected subordinates competing with non-infected dominants would pay higher costs than infected subordinates competing with infected dominants. We also predicted that these occurrence-mediated costs of infection would be ameliorated in infected dominant birds. We found that social status and the occurrence of parasites in competitors significantly interacted to change haematocrit in infected birds. Namely, subordinate and dominant infected birds differed in haematocrit depending on the infection status of their competitors. However, in contrast to our prediction, dominants fared better with infected subordinates, whereas subordinates fared better with uninfected dominants. Moreover, we found additional effects of parasite occurrence on mortality in canaries. Ultimately, we provide evidence for costs of parasitism mediated by social rank and the occurrence of parasites in competitors in a vertebrate species. This has important implications for our understanding of the evolutionary processes that shape parasite virulence and group living. © 2013 Australian Society for Parasitology Inc.Financial support was provided by the Région Bourgogne (France), the CNRS (France; Programme MIE) and the ANR (IRMAL) (France). http://dx.doi.org/10.1016/j.ijpara.2013.05.008Peer Reviewe