LB 12-155 - Detection of transmissible cancer lineages in basket cockles (Clinocardium nuttallii) in Puget Sound, Washington with multiple mitochondrial replacement events.

Background/Question/Methods:

The basket cockle (Clinocardium nuttallii) is an important part of the culture and diet of the Suquamish and other Coast Salish Tribes, and cockles’ decline has resulted in a plan to establish a hatchery and increase their numbers. Prior to the establishment of a hatchery for C. nuttallii in Puget Sound, Washington, a histological survey identified disseminated neoplasia, a cancer that circulates through the hemolymph system of infected animals, in a population targeted for use as brood stock. This finding prompted further questioning: Could the disseminated neoplasia in cockles be transmissible? Transmissible neoplasia has been identified in Tasmanian devils, dogs, and 9 bivalve species to date. Bivalve transmissible neoplasias (BTN) are clonal lineages of disseminated neoplasia cells that are able to infect neighboring bivalves, spreading through the environment as an infectious disease. To identify BTN in the cockles, nuclear and mtDNA loci were sequenced in a collection of cockles from Agate Pass. A qPCR assay was created based on initial cancer-specific sequences for a high throughput survey of the cockles, allowing analysis of 11 more collections from the Puget Sound and Washington state coastline using cytology paired with qPCR and phylogenetic analysis to screen for BTN.

Results/Conclusions:

The resulting sequences provided evidence that disseminated neoplasia in cockles is a BTN. Notably, while nuclear markers show that all samples of CnuBTN1 come from a single lineage, the mitochondrial markers are all different, suggesting that mitochondrial genomes of this cancer have been replaced multiple times through its evolution. qPCR, for the first lineage of BTN (CnuBTN1), identified this lineage in three out of 11 locations. One cockle, however, was highly positive for disseminated neoplasia through cytological analysis, but negative for CnuBTN1. Further analysis showed that this was a second lineage (CnuBTN2), demonstrating that there are at least two lineages of cancer in basket cockles of Puget Sound. The presence of CnuBTN adds an extra layer of complication to seeding populations since the cancer is transmissible and potentially lethal to naïve animals. To maximize the hatchery and seeding project endeavors, the new information of CnuBTN will be essential when choosing populations for breeding and seeding purposes. Further analysis of the presence and prevalence of CnuBTN lineages in the Pacific Northwest as well as incorporation of new data into management tactics will protect the local cockle population moving forward and enable continued cultural connection with the species by local Tribes.