Similar parasite communities but dissimilar infection patterns in two closely related chickadee species

Abstract

ABSTRACT Hemosporidian parasite communities are broadly similar in Boulder County, Colorado, between two common songbirds––the Black-capped Chickadee (Poecile atricapillus) and Mountain Chickadee (Poecile gambeli). However, Mountain Chickadees appear more likely to be infected with Plasmodium and potentially experience higher infection burdens with Leucocytozoon in contrast to Black-capped Chickadees. We found that elevation change (and associated ecology) drives the distributions of these parasite genera. For Boulder County chickadees, environmental factors play a more important role in structuring hemosporidian communities than host evolutionary differences. However, evolutionary differences are likely key to shaping the probability of infection, infection burden, and whether an infection remains detectable over time. We found that for recaptured birds, their infection status (i.e. presence or absence of detectable parasite infection) tends to remain consistent across capture periods. We sampled 235 chickadees between 2017 and 2021 across a ∼1,500-m elevation gradient from low elevation (i.e. the city of Boulder) to comparatively high elevation (i.e. the CU Boulder Mountain Research Station). It is unknown whether long-term hemosporidian abundance trends have changed over time in our sampling region. However, we ask whether potentially disparate patterns of Plasmodium susceptibility and Leucocytozoon infection burden could be playing a role in the negative population trends of Mountain Chickadees. LAY SUMMARY Hemosporidians are a diverse group of vector-transmitted parasites that infect birds and include the genera Haemoproteus, Leucocytozoon, and Plasmodium (the cause of avian malaria). Whether the diversity of these parasites is shaped more by avian evolutionary history or environment is still unclear. We therefore surveyed two closely related avian species, the Black-capped Chickadee and Mountain Chickadee, for these parasites spanning a gradient of habitats shaped by elevation. We found that parasite communities differed more from elevation change than between Black-capped and Mountain Chickadees. Mountain Chickadees sampled at low elevation were more likely to be infected with Plasmodium parasites than Black-capped Chickadees. Mountain Chickadees also might experience a higher infection burden from Leucocytozoon parasites. Elevation change appears to be a strong driver of parasite community diversity, but chickadee evolutionary history might influence the probability of infection, infection burden, and whether infections remain detectable over time. RESUMEN Las comunidades de parásitos haemosporidianos son muy similares en el Condado de Boulder, Colorado, entre dos aves canoras comunes: Poecile atricapillus y P. gambeli. Sin embargo, los individuos de P. gambeli parecen tener más probabilidades de estar infectados con Plasmodium y potencialmente experimentan cargas de infección más altas con Leucocytozoon en contraste con los individuos de P. atricapillus. Encontramos que el cambio de elevación (y la ecología asociada) determina la distribución de estos géneros de parásitos. Para los individuos de Poecile del Condado de Boulder, los factores ambientales desempeñan un papel más importante en la estructuración de las comunidades haemosporidianas que las diferencias evolutivas del huésped. Sin embargo, es probable que las diferencias evolutivas sean clave para determinar la probabilidad de infección, la carga de infección y si una infección sigue siendo detectable con el tiempo. Encontramos que, para las aves recapturadas, su estado de infección (i.e., presencia o ausencia detectable de infección por parásitos) tiende a permanecer constante en los períodos de captura. Muestreamos 235 individuos de Poecile entre 2017 y 2021 a lo largo de un gradiente de elevación de aproximadamente 1500 m desde una elevación baja (i.e., la ciudad de Boulder) hasta una elevación comparativamente alta (i.e., la Estación de Investigación de Montaña de la Universidad de Colorado en Boulder). Se desconoce si las tendencias de abundancia de haemosporidios a largo plazo han cambiado con el tiempo en nuestra región de muestreo. Sin embargo, nos preguntamos si los patrones potencialmente dispares de susceptibilidad al Plasmodium y la carga de infección de Leucocytozoon podrían estar desempeñando un papel en las tendencias poblacionales negativas de P. gambeli.