Background Changes in host phenotype following parasite infection are often considered as host manipulation when they seem advantageous for the parasite. However, putative cases of host manipulation by parasites are rarely tested in field-realistic conditions. Infection-induced phenotypic change cannot be conclusively considered as host manipulation if no evidence shows that this trait is adaptive for the parasite in the wild. Plasmodium sp., the parasites causing malaria in vertebrates, are hypothesized to “manipulate” their host by making their odour more attractive to mosquitoes, their vector and final host. While this is fairly well supported by studies on mice and humans, studies focusing on avian malaria give contradictory results. Methods In the present study, genotyped birds at different stages (uninfected, acute and chronic) of Plasmodium relictum infection were exposed, in a large outdoor aviary, to their natural vector, the mosquito Culex pipiens. Results After genotyping the blood meals of more than 650 mosquitoes, we found that mosquitoes did not bite infected birds more than they bit them before infection, nor more than they bit uninfected hosts. Conclusions Our study highlights the importance of testing ecological behaviours under natural conditions and suggests that different processes might be at play in mammals and birds regarding potential manipulation of attractiveness by malaria parasites. Graphical Abstract
Malaria is widespread throughout the world and affects many animal species. Although the origin of this vector-borne disease was discovered more than a century ago, several aspects of the within-host infection dynamic are still poorly understood. Among them, the factors triggering parasite recurrences – episodes of brief increase in parasite number following a period when the parasite was either absent or present at very low levels in the blood – have still not been clearly identified. Yet, recurrences may contribute significantly to overall infection prevalence in vertebrate host populations. Here, we investigated whether artificial or natural increases in stress hormone levels in chronically infected birds influence the replication rate of Plasmodium relictum and transmission to its natural vector, the mosquito Culex pipiens. Our results provide evidence that increased levels of corticosterone, either induced by oral ingestion or caused by handling stress, can trigger malaria recurrences. However, we did not observe any effect on the transmission rate of the parasite to the mosquito vector. Our study is a first fundamental step in understanding the mechanisms underlying malaria recurrences. It remains to be ascertained whether this feature extends to other malaria system and in particular to human malaria.
Co-infections with multiple pathogens are common in the wild and may act as a strong selective pressure on both host and parasite evolution. Yet, contrary to single infection, the factors that shape co-infection risk are largely under-investigated. Here, we explored the extent to which bird ecology and phylogeny impact single and co-infection probabilities by haemosporidian parasites using large datasets from museum collections and a Bayesian phylogenetic modelling framework. While both phylogeny and species attributes (e.g. size of the geographic range, life-history strategy, migration) were relevant predictors of co-infection risk, these factors were less pertinent in predicting the probability of being single infected. Our study suggests that co-infection risk is under a stronger deterministic control than single-infection risk. These results underscore the combined influence of host evolutionary history and species attributes in determining single and co-infection pattern providing new avenues regarding our ability to predict infection risk in the wild.
Continued advancements in environmental DNA (eDNA) research have made it possible to access intraspecific variation from eDNA samples, opening new opportunities to expand non-invasive genetic studies of wild animal populations. However, the use of eDNA samples for individual genotyping, as typically performed in non-invasive genetics, still remained unachieved. We present the first successful individual genotyping of eDNA obtained from snow tracks of three large carnivores: brown bear (Ursus arctos), European lynx (Lynx lynx) and wolf (Canis lupus). DNA was extracted using a protocol for isolating water eDNA and genotyped using amplicon sequencing of short tandem repeats (STR) and, for brown bear, a sex marker, on a high-throughput sequencing platform. Individual genotypes were obtained for all species, but genotyping performance differed among samples and species. Multilocus genotyping success for individual identification was higher for brown bear samples (6 over 7), than for wolf (7 over 10) and lynx (4 over 9) samples. The sex marker was genotyped in 5 out of 7 brown bear samples. Results for three species show that reliable individual genotyping, including sex identification, is now possible from eDNA in snow tracks, underlining its vast potential to complement the non-invasive genetic methods used for wildlife. To fully leverage the application of snow track eDNA, improved understanding of the ideal species- and site-specific sampling conditions, as well as laboratory methods promoting genotyping success are needed. This will also inform efforts to retrieve and type nuclear DNA from other eDNA samples, thereby advancing eDNA–based individual and population level studies.
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