The Chilean blue mussel has an independent transmissible cancer



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I used the Chilean blue mussel, Mytilus chilensis, to identify if the leukemia-like disease in this species is a conventional cancer or a transmissible cancer, as observed in other bivalves. To test this, I analyzed the DNA sequences of an intron-spanning region of the gene EF1 alpha (Elongation factor 1 alpha) to identify shared nucleotide polymorphisms only present in diseased individuals. Some neoplastic individuals contained more than two alleles, and normal individuals contained only two. Because bivalves are diploid organisms, I hypothesize the excess alleles belong to a cancer cell non-native to the host. Neoplastic individuals showed the presence of a common allele, giving evidence of horizontal transmission of a clonal cancerous cell. Further DNA sequence analysis indicated that the Mytilus chilensis potentially has a transmissible cancer lineage independent from the cancer lineage found in Mytilus trossulus, the blue mussel native to the Northern Pacific. The results of this study suggest that the evolution of transmissible cancers in the ocean are more common than previously thought.