Prevalence of blood parasites in European passeriform birds

Sensitive measure of prevalence and parasitaemia of haemosporidia from European blackbird (Turdus merula) populations: value of PCR-RFLP and quantitative PCR

Haemosporidian parasites are common in birds in which they act as an important selective pressure. While most studies so far have focused on the effect of their prevalence on host life-history traits, no study has measured the effect of parasitaemia. We developed molecular methods to detect, identify and quantify haemosporidia in 2 natural populations of the Blackbird Turdus merula. Three different parasite genotypes were found - 1 Haemoproteus and 2 Plasmodium. A PCR-RFLP screening revealed that only approximately 3% of blackbirds were free of parasites, compared to the 34% of uninfected birds estimated by blood smear screening. A quantitative PCR (q-PCR) assay revealed a weaker parasitaemia in microscopically undetected parasites compared to microscopically detected ones. Large parasitaemia differences were found between parasite species, suggesting either differing parasite life-histories or host resistance. Parasitaemias were also weaker in male hosts, and in urban habitats, suggesting that both host factors (e.g. immunity) and habitat characteristics (e.g. vector availability) may modulate parasite density. Interestingly, these differences in parasitaemia were comparable to differences in parasite prevalence estimated by smear screening. This suggests that previous results obtained by smear screening should be reinterpreted in terms of parasitaemia instead of parasite prevalence.

Distributions of exotic plants in eastern Asia and North America

Although some plant traits have been linked to invasion success, the possible effects of regional factors, such as diversity, habitat suitability, and human activity are not well understood. Each of these mechanisms predicts a different pattern of distribution at the regional scale. Thus, where climate and soils are similar, predictions based on regional hypotheses for invasion success can be tested by comparisons of distributions in the source and receiving regions. Here, we analyse the native and alien geographic ranges of all 1567 plant species that have been introduced between eastern Asia and North America or have been introduced to both regions from elsewhere. The results reveal correlations between the spread of exotics and both the native species richness and transportation networks of recipient regions. This suggests that both species interactions and human-aided dispersal influence exotic distributions, although further work on the relative importance of these processes is needed.

Diversity, distribution and exchange of blood parasites meeting at an avian moving contact zone

Research on contact zones has paid relatively little attention to host-parasite interactions, although these situations have important but different implications depending on whether one considers the host or the parasite's perspective. We investigated both the role of a host contact zone in parasite expansion and whether parasites could influence contact zone dynamics. We studied the diversity and the patterns of parasite exchange (genera Haemoproteus and Plasmodium) infecting two parapatric sibling passerines meeting at a moving contact zone in western Europe. We amplified and sequenced a fragment of the parasite cytochrome b gene. The expanding host harboured more diverse parasites, which might indicate a superior ability to face a diverse parasite fauna than the receding host. Prevalence was very high in both hosts, due to the frequent occurrence of two sister Haemoproteus lineages. Despite the recent movement of the contact zone, these two parasites fitted almost perfectly to the geographic range of their main host species. Yet, we found several cases of cross-species infection in sympatric areas and evidences of asymmetrical spreading of parasites from the expanding host towards the receding host. Altogether, our results suggest that the host contact zone mainly acts as a barrier to parasite expansion even if recurrent host shifts are observed. Besides, they also support the idea that parasite-mediated competition might contribute to the displacement of hosts' contact zones, thereby emphasizing the role of parasitism on the population dynamics of sympatric species.

Parasite prevalence and sample size: misconceptions and solutions

Parasite prevalence (the proportion of infected hosts) is a common measure used to describe parasitaemias and to unravel ecological and evolutionary factors that influence host-parasite relationships. Prevalence estimates are often based on small sample sizes because of either low abundance of the hosts or logistical problems associated with their capture or laboratory analysis. Because the accuracy of prevalence estimates is lower with small sample sizes, addressing sample size has been a common problem when dealing with prevalence data. Different methods are currently being applied to overcome this statistical challenge, but far from being different correct ways of solving a same problem, some are clearly wrong, and others need improvement.

Prevalence and differential host-specificity of two avian blood parasite genera in the Australo-Papuan region

The degree to which widespread avian blood parasites in the genera Plasmodium and Haemoproteus pose a threat to novel hosts depends in part on the degree to which they are constrained to a particular host or host family. We examined the host distribution and host-specificity of these parasites in birds from two relatively understudied and isolated locations: Australia and Papua New Guinea. Using polymerase chain reaction (PCR), we detected infection in 69 of 105 species, representing 44% of individuals surveyed (n = 428). Across host families, prevalence of Haemoproteus ranged from 13% (Acanthizidae) to 56% (Petroicidae) while prevalence of Plasmodium ranged from 3% (Petroicidae) to 47% (Ptilonorhynchidae). We recovered 78 unique mitochondrial lineages from 155 sequences. Related lineages of Haemoproteus were more likely to derive from the same host family than predicted by chance at shallow (average LogDet genetic distance = 0, n = 12, P = 0.001) and greater depths (average distance = 0.014, n = 11, P < 0.001) within the parasite phylogeny. Within two major Haemoproteus subclades identified in a maximum likelihood phylogeny, host-specificity was evident up to parasite genetic distances of 0.029 and 0.007 based on logistic regression. We found no significant host relationship among lineages of Plasmodium by any method of analysis. These results support previous evidence of strong host-family specificity in Haemoproteus and suggest that lineages of Plasmodium are more likely to form evolutionarily-stable associations with novel hosts.