Hydra oligactis, a freshwater creature related to jellyfish and sea anemones, considered “amaranth” in many ways, which reproduces asexually, can develop tumors if overfed, and these are passed on to its clone offspring.
Hydra without tumors (a) and with tumors (b). (Tissot et al, Proceedings of the Royal Society B, 2024)
These hydras can create a contagious form of cancer, notes ScienceAlert, which describes a new study published in the Proceedings of the Royal Society B on this bizarre phenomenon, which not only reveals details of how the process works in these creatures, but also helps to better understanding of transmissible forms of cancer in general.
While tumors are an inevitable risk of being multicellular, there are fortunately few examples of cancer that can be transmitted between individuals. Of these, the best known are two that affect the Tasmanian devil, another example is that that affects dogs, and 11 have been observed in bivalve creatures.
It is very important to understand how contagious cancers occur, primarily in order to somehow avoid them in our own species, but also in the hope of protecting other beings from the terrible suffering that, for example, Tassie devils face from the disease their facial tumors.
Evolutionary ecologist Sophie Tissot of the French National Center for Scientific Research (CNRS) and her team traced the origin of contagious cancers.
The experiment of a decade and a half ago
In a laboratory experiment 15 years ago, a freshwater creature related to jellyfish and sea anemones developed spontaneous tumors in response to overfeeding.
It is Hydra oligactis, considered “amaranth” in many ways, which reproduces asexually, cloning itself by forming tiny buds that break off to grow into a physically separate but genetically identical creature.
The first experimental observation of the evolution of a transmissible tumor
This, along with its propensity to form tumors under laboratory conditions, presents potential for genetic research into cancer development.
Sophie Tissot and her team set out to demonstrate how valuable this model can be for understanding the evolution of transmissible cancers.
“Using Hydra oligactis, which exhibits spontaneous tumor development that, in some strains, has become vertically transmitted, this study presents the first experimental observation of the evolution of a transmissible tumor. (…) Therefore, athis work makes the first contribution to understanding the conditions under which transmissible cancer occurs and their short-term consequences for the host“, say the authors.
The researchers collected 50 hydras from Lake Montaud in France and prepared them for a life in the laboratory.
To ensure a high rate of tumor development, budding, and thus increasing the chances of tumor transmission, the researchers fed some of these polyps with an excessive amount of shrimp larvae, five times a week, mimicking the conditions that caused tumor development in a previous study.
From these overfed hydras, 19 that were full of tumors after two months were selected, and their buds were collected and grown under the same conditions. The researchers followed this process over five “generations” of tumor-forming clonal buds, selecting them from their tumor-free peers to give rise to the next generation.
To make sure the tumors were passed down from the parents and didn’t appear spontaneously every generation, the researchers looked at the hydra’s cancer-free offspring.
Which hydras were more likely to develop tumors
Hydras from parents who had tumors were four times more likely to develop tumors than those whose parents did not have tumors, even though all the hydras were genetically identical.
The researchers thus confirmed that tumors can indeed be induced in Hydra oligactis and that the transmission rate can increase over time.
In addition, they observed, fifth-generation hydra bearing transmissible tumors began to show changes in life-history traits compared to their tumor-free counterparts. All of this led to increased investment in asexual reproductive efforts before the tumor had a chance to develop, and budding slowed down after the tumor appeared.
This appears to go hand in hand with another change, in which bud mortality was greater after the emergence of tumors.
“These changes suggest an adjustment of host traits to offset tumor costs by producing more buds when they are more likely to survive and remain tumor-free.”Tissot and his colleagues show.
The researchers note that the rarity of transmissible cancers may be more due to a lack of suitable environmental conditions for their spread, as, at least in this study, acquiring transmissibility did not appear to be a problem for the tumor cells.
Researchers say that if this is true, “it is essential to consider these aspects in the study of ecosystems disturbed by human activities, as they could potentially alter the conditions that favor the spread of transmissible cancers”.
