Limited movement of an avian hybrid zone in relation to regional
variation in magnitude of climate change
Abstract
Studies of natural hybrid zones can provide documentation of range
shifts in response to climate change and identify loci important to
reproductive isolation. Using a deep temporal (36-38 years) comparison
of the black-capped (Poecile atricapillus) and Carolina (P.
carolinensis) chickadee hybrid zone, we investigated movement of the
western portion of the zone (western Missouri) and assessed whether loci
and pathways underpinning reproductive isolation were similar to those
in the eastern portion of the hybrid zone. Using 92 birds sampled along
the hybrid zone transect in 2016 and 68 birds sampled between 1978 and
1980, we generated 11,669 SNPs via ddRADseq. These SNPs were used to
assess movement of the hybrid zone through time and to evaluate
variation in introgression among loci. We demonstrate that the interface
has moved ~5 km to the northwest over the last 36-38
years, i.e., at only one-fifth the rate at which the eastern portion
(e.g., Pennsylvania, Ohio) of the hybrid zone has moved. Temperature
trends over the last 38 years reveal that eastern areas have warmed 50%
more than western areas in terms of annual mean temperature, possibly
providing an explanation for the slower movement of the hybrid zone in
Missouri. Our results suggest hybrid zone movement in broadly
distributed species, such as chickadees, will vary between areas in
response to local differences in the impacts of climate change.