Hybrid zones can provide clear 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 under-sampled western portion of
the zone (western Missouri) as well as investigating whether loci and
pathways underpinning reproductive isolation were similar to those from
the eastern portion of the hybrid zone. Using 92 birds sampled along the
hybrid zone transect in 2016, 68 birds sampled between 1978 and 1980,
and 5 additional reference birds sampled from outside the hybrid zone,
we generated 11,669 SNPs via ddRADseq. We used these SNPs to interpolate
spatially and assess the movement of the hybrid zone interface through
time, and to assess variation in introgression among loci. We
demonstrate that the interface has moved approximately 5-8 km to the
northwest over the last 36-38 years, i.e., at only one-fifth the rate at
which the eastern portion of the hybrid zone (e.g. Pennsylvania, Ohio)
has moved. Temperature trends across 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. Using genomic cline
analyses, we detected four genes that showed restricted introgression in
both Missouri and Pennsylvania, including Pnoc, a gene involved in
metabolism, learning and memory, concordant with previous physiological
and behavioral findings on hybrids and the parental species.
Reproductive Success Across The Black-Capped Chickadee (Poecile Atricapillus) and Carolina Chickadee (P. Carolinensis) Hybrid Zone in Ohio