Search for: All records

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. 

Abstract We studied hybridization between the Black-crested and Tufted titmouse across two geographically distinct transects that differ in the timing of secondary contact by hundreds to thousands of years. We found that hybridization patterns correspond to localized hybrid swarms and that the titmouse hybrid zone is likely slowly expanding over time, a product of short post-natal dispersal distances coupled with weak or absent selection against admixture. We show the southern part of the hybrid zone located in Texas is four times wider than the northern region of hybridization in Oklahoma, which is likely due to geographic differences in hybrid zone age. Despite differences in width, most individuals in both transects are advanced-generation hybrids and backcrosses, suggesting geographically consistent hybridization dynamics. We documented a strong correlation between genotypes and plumage index, suggesting that hybridization has not yet resulted in the decoupling of plumage and genome-wide ancestry as observed in some other avian hybrid zones. Although our results suggest the ongoing expansion of the hybrid zone, the rate of expansion appears to be slow, on the scale of tens of meters a year, and it will likely take hundreds of thousands to millions of years before homogenization of the parental populations. While we did not find support for partial reproductive isolation in the hybrid zone itself, there is the possibility that ecological or sexual selection limits introgression into allopatric regions. Broadly, the results of our study highlight the value of multiple, geographically distant, transects across a hybrid zone for assessing the evolutionary dynamics of hybridizing lineages.