What happens when species with similar phenotypes experience secondary contact? Introducing our @biorxivpreprint: Cryptic and extensive hybridization between ancient lineages of American crows. biorxiv.org/content/early/… 
Most species and most hybrid zones have historically been described based on phenotypes, but speciation and hybridization can also occur with negligible phenotypic differentiation. biorxiv.org/content/early/…
American and Northwestern crows are longstanding taxonomic species with a continuous distribution on the Pacific coast of North America. They lack reliable traditional characters for identification. biorxiv.org/content/early/…
We wanted to know whether they are genetically differentiated and the extent to which they hybridize, and we looked into their genomes to find out.
We found evidence in both nuclear DNA and mitochondrial DNA that American and Northwestern crows have distinct evolutionary histories.
They seem to have diverged in the late Pleistocene (~380,000 years ago), when periods of extensive glaciation may have kept American Crows south of the ice sheets and trapped Northwestern Crows in ice-free refugia in Alaska or Haida Gwaii. biorxiv.org/content/early/…
The hybrid zone between American and Northwestern crows is very wide, stretching along >1,500 km (>900 miles) of the Pacific coast in Washington and British Columbia. biorxiv.org/content/early/…
Most of the gene flow seems to be along a north-south axis, to the west of the Cascades and Coast Mountains.
The mitochondrial DNA cline was steeper than the nuclear DNA cline, consistent with Haldane's rule, except that the very wide hybrid zone makes strong selection against hybrids seem unlikely. biorxiv.org/content/early/…
The hybrid zone consists of a swarm of late-generation hybrids and backcrosses, not F1 or recent-generation hybrids. biorxiv.org/content/early/…
Big picture: it looks like American and Northwestern crows were once evolving independently, but their lineages are now fusing back together. biorxiv.org/content/early/…
American and Northwestern crows began the speciation process at least once, but didn't finish it. When their ranges came back together, they resumed interbreeding. Can't tell American and Northwestern crows apart? Don't feel bad, because neither can they. biorxiv.org/content/early/…
Thanks to coauthors for a fascinating study, and special thanks to coauthor Kevin Epperly for also doing the original crow illustration for Figure 1. If you zoom in on the PDF you can start to see just how incredibly talented this guy is. biorxiv.org/content/early/…
TL;DR for fellow crow watchers out there in and around Seattle, Vancouver, Victoria: All our crows are hybrids, but we can still love them. biorxiv.org/content/early/…
TL;DR for bird listers: Seems likely that the checklist committee will eventually lump Northwestern Crow given how wide the hybrid zone is, but this research isn't peer-reviewed quite yet. biorxiv.org/content/early/…
To clarify, if you want to read the whole manuscript, it's available here for free:
biorxiv.org/content/biorxi…
biorxiv.org/content/biorxi…
Cc: @VictoriaNHS
