A specimen representing the first-generation male offspring of a female narwhal and a male beluga has been identified by analyzing genes sampled from a skull found in West Greenland in 1990. The findings, which are presented in Scientific Reports, represent the only known evidence of potential hybridization between belugas and narwhals.
Mikkel Skovrind, Eline Lorenzen and colleagues analysed genomic DNA extracted from the teeth of the skull, which is stored at the Natural History Museum of Denmark. The authors compared the skull’s DNA to DNA from the genomes of eight live belugas and eight live narwhals sampled in the same area in West Greenland where the skull was found. The analysis suggests that the specimen was 54% beluga and 46% narwhal. The authors used the ratio between the number of X chromosomes and the number of autosomes - a common method to determine the sex of an individual ― to infer that the hybrid was male. Analysis of the mitochondrial genome, a small part of the total DNA of an individual that is only transmitted via the female germline, suggested that the hybrid’s mother was a narwhal.
The authors also analysed variants (isotopes) of the chemical elements carbon and nitrogen contained in bone collagen extracted from the skull and compared it to bone collagen from a reference panel of 18 narwhal and 18 beluga skulls. The concentration of carbon isotopes in the samples from the skull was higher than that in the other skulls, suggesting that the hybrid’s diet was different from either parent species. From this, the authors infer that the hybrid foraged closer to the bottom of the seafloor (in the benthic zone) than narwhals and belugas.