ABSTRACT
Emperor Geese (Anser canagicus) are iconic waterfowl endemic to Alaska and adjacent areas of northeastern Russia that are considered to be near threatened by the International Union for Conservation. This species has been identified as harboring diverse viruses and parasites which have, at times, been associated with disease in other avian taxa. To better assess if disease represents a vulnerability for Emperor Geese breeding on the Yukon-Kuskokwim Delta, Alaska, we evaluated if haemosporidian parasites were associated with decreased mass or survival among adult female nesting birds captured during 2006-2016. Through molecular analyses, we detected genetically diverse Leucocytozoon, Haemoproteus, and Plasmodium parasites in 28%, 1%, and 1% of 607 blood samples screened in triplicate, respectively. Using regression analysis, we found evidence for a small effect of Leucocytozoon infection on the mass of incubating adult female Emperor Geese. The estimated mass of infected individuals was approximately 43 g (95% CI: 20-67 g), or approximately 2%, less than uninfected birds when captured during the second half of incubation (days 11-25). We did not, however, find support for an effect of Leucocytozoon infection on survival of adult female nesting Emperor Geese using a multi-state hidden Markov framework to analyze mark-resight and recapture data. Using parasite mitochondrial DNA cytochrome b sequences, we identified 23 haplotypes among infected Emperor Geese. Leucocytozoon haplotypes clustered into three phylogenetically supported clades designated as 'L. simondi clade A', 'L. simondi clade B', and 'other Leucocytozoon'. We did not find evidence that parasites assigned to any of these clades were associated with differential mass measures among nesting adult female Emperor Geese. Collectively, our results provide negligible evidence for Leucocytozoon parasites as causing detrimental effects to adult female Emperor Geese breeding on the Yukon-Kuskokwim Delta.
ABSTRACT
Haemosporidian parasites may impact avian health and are subject to shifts in distribution and abundance with changing ecologic conditions. Therefore, understanding variation in parasite prevalence is important for evaluating biologically meaningful changes in infection patterns and associated population level impacts. Previous research in western Alaska, US, indicated a possible increase in Leucocytozoon spp. infection between Emperor Geese (Anser canagicus) sampled in 1996 (<1%, n=134) and during 2011-12 (19.9%, 95% confidence interval [CI]: 3.0-36.8%, n=77); however, different detection methods were used for these estimates. Prior research in this same region identified a lack of Leucocytozoon spp. parasites (0%, n=117) in sympatrically breeding Cackling Geese (Branta hutchinsii minima) in 2011. We molecularly screened blood samples collected from sympatrically breeding Emperor and Cackling Geese in western Alaska during additional breeding seasons to better assess temporal and species-specific variation in the prevalence of blood parasites. We found similar prevalence estimates for Leucocytozoon spp. parasites in Emperor Goose blood samples collected in 1998 and 2014, suggesting consistent infection of Emperor Geese with blood parasites at these time points. Using samples from sympatric geese sampled during 2014, we found evidence for a higher incidence of parasites among Emperor Geese (20.3%, 95% CI: 11.8-32.7%) compared to Cackling Geese (3.6%, 95% CI: 1.1-11.0%), reinforcing the previous finding of species-specific differences in infection. Furthermore, we detected Leucocytozoon, Haemoproteus, and Plasmodium spp. blood parasites in unflighted goslings of both species, supporting the possible transmission of these parasites at western Alaska breeding grounds. Our results help to clarify that prevalence of Leucocytozoon spp. parasites have probably remained consistent among Emperor Geese breeding in western Alaska since the late 1990s and that this species may disproportionally harbor Leucocytozoon spp. compared to sympatrically breeding Cackling Geese.
