Genetic confirmation of a hybrid between two highly divergent cardinalid species: A Rose-breasted Grosbeak (Pheucticus ludovicianus) and a Scarlet Tanager (Piranga olivacea)

Using low-coverage whole-genome sequencing, analysis of vocalizations, and
inferences from natural history, we document a first-generation hybrid
between a rose-breasted grosbeak (Pheucticus ludovicianus) and a scarlet
tanager (Piranga olivacea). These two species occur sympatrically
throughout much of eastern North America, although were not previously
known to interbreed. Following the field identification of a putative
hybrid, we use genetic and bioacoustic data to show that a rose-breasted
grosbeak was the maternal parent and a scarlet tanager was the paternal
parent of the hybrid, whose song was similar to the latter species. These
two species diverged >10 million years ago, and thus it is
surprising to find a hybrid formed under natural conditions in the wild.
Notably, the hybrid has an exceptionally heterozygous genome, with a
conservative estimate of a heterozygous base every 100 bp. The observation
that this hybrid of such highly divergent parental taxa has survived until
adulthood serves as another example of the capacity for hybrid birds to
survive with an exceptionally divergent genomic composition.