Hooded crow and Carrion Crow Nature.2014.15436

Background Information

• Two types of crows: carrion crows (Corvus corone) and hooded crows (Corvus cornix)

• Geographic distribution:

  • Carrion crows dominate the west

  • Hooded crows dominate the east

  • A narrow strip in central Europe is where they have been known to interbreed for about 10,000 years.

Genetic Similarity

• Despite their appearance, the two species are almost identical genetically.

• Taxonomic debate existed since:

  • 1758: Carl Linnaeus classified them as separate species.

  • 19th century: Darwin argued that classifying them was impossible without a clear definition of 'species'.

• Current understanding:

  • They can cross-breed and produce viable offspring, suggesting a lack of reproductive barriers.

  • Proposed classification as subspecies of carrion crow.

Research Findings

• Jochen Wolf and colleagues found:

  • Crows in the hybrid zone show greater genetic similarity to hooded crows compared to those in separate geographical areas (west).

  • Less than 0.28% of the genome differs between these populations, primarily on chromosome 18.

  • This chromosome region is linked to pigmentation, visual perception, and hormonal regulation.

• Key differences between crows:

  • Coloration differs: carrion crows are solid black, hooded crows are grey.

  • Mating preferences: each prefers mates with similar coloration.

  • Social behavior influenced by hormones: carrion crows exhibit dominant behaviors over hooded crows.

Evolutionary History

• Suggested divergence from a common ancestor occurred after glacial periods isolated populations.

• Once ice sheets retreated, populations began cross-breeding again, interrupting divergence.

Mating Preferences and Stability

• Study discusses the historical preference for mating within distinct groups:

  • This preference may help maintain distinctions between populations.

• Potential outcomes of gene flow:

  • Wolf suggests mix may stabilize; mate-choice regions could resist influence from other genes.

  • Predicts that hooded crows could start to resemble the more socially dominant carrion crows over time.

• Counterpoint by Peter de Knijff:

  • Suggests that genetic flow primarily moves from hooded to carrion crows.

  • Believes that the integration of hooded traits by carrion crows is inevitable.

Species Concept Discussion

• De Knijff emphasizes the irrelevance of species classification for the birds themselves, suggesting it's a human construct.

• Wolf also sidesteps the species debate by focusing on the genetic findings rather than taxonomic labels.