A jellyfish-like creature called a hydra can develop a contagious form of cancer if overfed, and the tumors can be passed on to its clones.
A new study on this bizarre phenomenon not only reveals details about the process in hydra, but also improves understanding of transmissible forms of cancer in general. Although tumors are an inevitable risk for multicellular beings, there are very few cases of cancer that can be transmitted between individuals. The best known are two affecting the Tasmanian devil, another case affecting dogs, and there are 11 examples observed in bivalves.
Of course, we are interested in understanding how contagious cancers arise, both to avoid such a situation in our species and to protect other creatures, such as Tasmanian devils, who suffer from facial tumor disease. However, these cases of transmissible cancer were well documented when they were discovered, which led evolutionary ecologist Sophie Tissot of the French National Center for Scientific Research (CNRS) and her team to take a different approach to trace the origin of these cancers.
Hydras develop a contagious form of cancer if they eat too much
Conveniently, a freshwater creature related to jellyfish and sea anemones spontaneously developed a contagious form of cancer in a lab experiment 15 years ago in response to overfeeding.
Hydra oligactisa freshwater creature considered “immortal” in many ways, reproduces asexually, cloning itself by forming small buds that separate and grow into a physically distinct but genetically identical creature. This ability, along with its propensity to form tumors under laboratory conditions, makes it an ideal model for investigating the genetics of cancer development. Tissot and his colleagues set out to show how valuable this creature can be in understanding the evolution of transmissible cancers.
“Using Hydra oligactiswhich spontaneously develop tumors, and in some cases they become vertically transmitted, this study presents the first experimental observation of the evolution of a transmissible cancer”, write the authors.
How are tumors transmitted in these creatures?
The researchers collected 50 hydras from Lake Montaud, France, and moved them to the laboratory. To ensure a high rate of tumor development, they overfed some of the creatures five times a week, replicating the conditions that caused the tumors to develop in a previous study. After two months, 19 of the overweight and tumor hydras were selected, and their buds were collected and grown under the same conditions, a process repeated for five generations.
To confirm that the tumors were passed down from the parents, the researchers compared hydra offspring from parents with tumors to those whose parents did not have tumors. Hydras from parents with tumors were four times more likely to develop tumors, even though all the hydras were genetically identical.
The study confirmed that tumors can be induced at H. ligactus and that their transmission rate may increase over time. In addition, the fifth generation of hydra bearing transmissible tumors showed changes in reproductive traits, investing more in asexual reproduction before tumors developed, with a higher bud mortality rate after tumors appeared, writes Science Alert.
“These changes suggest an adaptation of the organism’s traits to offset the costs of the tumor, by producing more buds when they are more likely to survive and remain tumor-free,” Tissot and colleagues explain.
The study concluded that the rare cases of transmissible cancers may be related to the lack of suitable environmental conditions for their spread, suggesting that human activities that disrupt ecosystems could change the conditions favorable to the spread of this type of cancer.
This research was published in Proceedings of the Royal Society B.
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Source: www.descopera.ro
