Origin Stories: Cancer in Bivalves

Written by on December 14, 2016 in Marine Life

By Astrid Hsu

What if cancer spread the like common cold? A hug, a cough, or sharing food would put the entire population at risk. Luckily, humans are currently safe from such a scenario. Unfortunately, the same cannot be said for our marine bivalve friends.

Cockles, Cerastoderma edule. Photo credit: Féron Benjamin - Flickr, CC BY-SA 2.0.

Cockles, Cerastoderma edule. Photo credit: Féron Benjamin – Flickr, CC BY-SA 2.0.

Initially discovered in soft-shell clams (Mya arenaria), a contagious cancer called disseminated neoplasia (similar to leukemia) was found in mussels (Mytilus trossulus), cockles (Cerastoderma edule), and golden carpet shell clams (Polititapes aureus) in a recent study. Researchers concluded that cancer in these species was contagious because the DNA of tumor cells were distinct from that of their host but nearly identical to each other. Each species has a different origin story of how their cancer came to be.

For the soft-shell clam, all infected members have same tumor cell, implying that the disease sprouted from one unfortunate individual of M. arenaria. Mussels and cockles echo this pattern, with cancer cells derived from one original host, respectively. However, analysis on golden carpet shell clams discovered that while the disease was clearly transmissible, the genetic structure of tumor cells was strikingly similar to that of P. aureus’ neighbor, the pulled carpet shell (Venerupis corrugata). These two species reside in the same region—even in the same beds—and this proximity and genetic evidence indicate that not only is cancer transmissible within a species but that it can cross to other species. However, further confounding scientists, there has been little incidence of leukemia-like cancer in the pulled carpet shell despite monitoring since 1990.

The cancerous bivalves present not only health conundrums but also threaten the seafood industry and ecological state. Shellfish is a $329 million industry in the US alone and represents two-thirds of the nation’s aquaculture industry. Bivalves also perform countless ecosystem services, from stabilizing habitats and promoting fish diversity to filtering water and acting as carbon sinks. Thus, transmissible disease has the power to heavily damage economies and ecosystems tied to shellfish. But with researchers working to understand the genetic and ecological factors, there is hope that conservationists will help bivalves beat cancer into remission and conserve the ecosystem and market.

Copyright © 2016 by Marine Science Today, a publication of Marine Science Today LLC.

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