Haemosporidian prevalence and community composition vary little across a chickadee hybrid zone

Within animal hybrid zones, parasites may determine competitive outcomes between host species and thus affect hybridization dynamics. We addressed this hypothesis by evaluating haemosporidian prevalence and community composition in a rapidly moving hybrid zone between Black-capped Chickadees (Poecile atricapillus) and Carolina Chickadees (P. carolinensis). Using molecular methods, we screened for haemosporidians in multiple chickadee populations across the hybrid zone and investigated whether parasite prevalence varied as a function of admixture among these birds. We identified 36 parasite lineages from 3 haemosporidian genera (Plasmodium, Haemoproteus, and Leucocytozoon) but found no genera or lineages more likely to infect any particular chickadee taxon. Instead, haemosporidian prevalence varied across sites and seasons: Leucocytozoon was more prevalent during chickadees' breeding season, whereas Haemoproteus prevalence peaked during nonbreeding periods. Leucocytozoon infected proportionally fewer birds at the leading edge of the hybrid zone than near its center. However, haemosporidian communities were similar among chickadee populations, and evidence for parasite exchanges between chickadee taxa was lacking. These results underscore the complexity of bird-parasite relationships and suggest that haemosporidians are unlikely to play a major role in the ongoing movement of this hybrid zone.

Automated summary

Within animal hybrid zones, haemosporidian prevalence showed seasonal and spatial variation among chickadee populations, but there was no evidence of parasite exchanges between different chickadee taxa. These results suggest that haemosporidians are unlikely to play a significant role in the movement of the hybrid zone.