Coevolution with hosts underpins speciation in brood parasitic cuckoos

Coevolution is considered to be a likely driver of speciation, but
evidence linking macroevolutionary patterns to microevolutionary processes
is scarce. We report that coevolution with hosts drives divergence in
bronze-cuckoos. Bronze-cuckoo hosts reject cuckoo nestlings, selecting for
mimicry of host nestlings by cuckoos. This has generated a diversity of
bronze-cuckoo nestling morphologies matching those of their respective
hosts across their geographic range and promotes diversification in
sympatry; little bronze-cuckoos that exploit multiple host species in
sympatry show evidence of genetic differentiation and corresponding
divergence in nestling morphology. This process is reflected in
macroevolutionary patterns: rates of speciation are faster in virulent
cuckoos than in more benign species and simulation models indicate greater
support for a sympatric mode of speciation in bronze-cuckoos than in
sister taxa.