Biogeographical patterns and co-occurrence of pathogenic infection across island populations of Berthelot’s pipit (Anthus berthelotii)

Abstract

Pathogens can exert strong selective forces upon host populations. However, before we can make any predictions about the consequences of pathogen-mediated selection, we first need to determine whether patterns of pathogen distribution are consistent over spatiotemporal scales. We used molecular techniques to screen for a variety of blood pathogens (avian malaria, pox and trypanosomes) over a three-year time period across 13 island populations of the Berthelot's pipit (Anthus berthelotii). This species has only recently dispersed across its range in the North Atlantic, with little subsequent migration, providing an ideal opportunity to examine the causes and effects of pathogenic infection in populations in the early stages of differentiation. We screened 832 individuals, and identified two strains of Plasmodium, four strains of Leucocytozoon, and one pox strain. We found strong differences in pathogen prevalence across populations, ranging from 0 to 65%, and while some fluctuations in prevalence occurred, these differences were largely stable over the time period studied. Smaller, more isolated islands harboured fewer pathogen strains than larger, less isolated islands, indicating that at the population level, colonization and extinction play an important role in determining pathogen distribution. Individual-level analyses confirmed the island effect, and also revealed a positive association between Plasmodium and pox infection, which could have arisen due to dual transmission of the pathogens by the same vectors, or because one pathogen lowers resistance to the other. Our findings, combined with an effect of infection on host body condition, suggest that Berthelot's pipits are subject to different levels of pathogen-mediated selection both across and within populations, and that these selective pressures are consistent over time.

The influence of vagrant hosts and weather patterns on the colonization and persistence of blood parasites in an island bird

“…Two lines of evidence, however, suggest that the dispersal of vagrant silvereyes has little influence on these dynamics. A growing number of studies have demonstrated differences in haemosporidian parasite frequencies between island and mainland populations despite regular arrivals of dispersing avian hosts (Beadell et al, 2007;Spurgin et al, 2012;P erez-Rodr ıguez et al, 2013), and our results suggest that parasite host-specificity could explain this phenomenon. Second, the observed detection probabilities across years for Haemoproteus and Plasmodium lineages in island silvereyes were substantially different from those expected under models that sample from the mainland parasite distribution based on realistic scenarios of vagrant arrivals.…”

Genomic associations with bill length and disease reveal drift and selection across island bird populations

“…() and Spurgin et al. (). Pipits caught on the alpine plateau of El Teide volcano (>2000 m above sea level) were classified as a separate population (Spurgin et al.…”

Drift, not selection, shapes toll‐like receptor variation among oceanic island populations

“…We have also shown that these populations are exposed to spatially varying pathogen pressures that are consistent over time (Spurgin et al . ) and that MHC genes are rapidly evolving across the populations as a result of gene conversion and positive selection (Spurgin et al . ).…”