Do phylogeny and habitat influence admixture among four North American chickadee (family: Paridae) species

Hybridization is an important aspect of speciation, yet questions remain
about the ecological and environmental factors that influence
hybridization among wild populations. We used microsatellite genotyping
data and collected land cover and environmental data for four North
American chickadee species: black-capped Poecile atricapillus, mountain P.
gambeli, chestnut-backed P. rufescens and boreal P. hudsonicus chickadees.
Combining these datasets, we sought to examine whether there is evidence
of admixture between four widely distributed North American chickadee
species; whether admixture takes place more often between more closely
related species pairs or between species pairs with more similar
ecological preferences; and whether certain habitat types have higher
rates of admixture than others. We detected admixture for five of the six
species pairs analyzed (chestnut-backed–mountain chickadee pair showed no
evidence of admixture), and found rates of admixture varied
geographically, and within taxa pairs. Admixture was higher among less
closely related species than more closely related species, although
habitat similarity was not a significant predictor. Finally, rates of
admixture were higher in urban parkland habitats than deciduous, mixed or
coniferous forest habitats. Our work indicates admixture occurs frequently
among North American parids, and habitat and environmental variation may
play an important role in the frequency and geographic distribution of
hybridization.