Cancer Discovered in Hydra?

It has recently been reported here and here that scientists at Kiel University in Germany claim that cancer has been found in Hydra.

Anyone familiar with my published theory knows it asserts that lethal juvenile cancer occurred in all Bilaterians and only in Bilaterians, that other multicells including cnidarians like Hydra did not experience it during evolution.

So does this report from Kiel University conflict with my theory? 

Is it cancer? In the original paper by the Kiel scientists I read that the specimen with the tumor displayed lower fitness than unaffected specimens: it had fewer offspring. But the paper does not report that the specimen was killed by its “tumor.” Contrast that with the 1969 report of lethal neoplasms in Drosophila by Gateff and Schneiderman (1). Before describing their own findings, the authors offered in their opening sentence the following terse summary complete with scare quotes, “More than a hundred papers have been published describing abnormal lesions in insects which have been called “tumors” or “neoplasms," [but]  “None of the tumors are lethal to their hosts.” As for their own findings, “In this paper we report what appears to be a true neoplasm in Drosophila and one of the first repeatedly transplantable lethal neoplasms found in any invertebrate.” (Emphasis added.)

Although the 2014 Hydra researchers did manage to transplant successfully cells from the tumor to another specimen I consider it most significant that neither the original host nor the recipient Hydra was killed by the tumor.

Is it possible that the affliction identified in Hydra is more comparable to crown gall disease found in some plants and frequently—and in my opinion, incorrectly—called “cancer” instead of the phenomenon described by Gateff and Schneiderman?

I recall that when I first embarked on this project and read in the Britannica that plants can get cancer my initial reaction was, “That doesn't make sense.”  Plants depend on exposure to intense UV radiation, a powerful carcinogen, so the suggestion that they survived for hundreds of millions of years while possessing in every somatic cell a cancer-initiating mechanism that could be triggered by UV radiation defies evolutionary logic. (2) Is it worthwhile applying the same logic to the question “Is it possible for Hydra to die of cancer?”

Comparing evolutionary histories. As I summarize in Chapter Two of my book for about 400 million years all Bilaterian gene pools produced animals that shielded somatic cells from direct exposure to radiation. The earliest Bilaterians lived in the sea bottom, a habitat providing maximum protection from UV and cosmic radiation. Their close descendants survived on the sea bottom, a slightly more risky habitat, but all of those bottom-dwellers possessed heavy non-cellular external coverings. When some Bilaterians finally did emerge from the marine environment many of those equipped with immune systems capable of killing cancer cells—the vertebrates—dropped their external shields but all terrestrial invertebrates—arthropods and mollusks—which lack such post-transformational anti-cancer defenses, retained them. In contrast, Hydra’s history implies they had nothing to fear from UV radiation; their bodies are not shielded, they possess no protective pigmentation and they survive in habitats offering little protection from radiation.

 

The absence of senescence.  In a concluding paragraph the authors wrote the following, “As Hydra is a rare example of an animal that can control senescence, our findings also imply that even a literally immortal organism is not immune from developing disseminating and fitness reducing tumors.”

I am convinced, and have published, that senescence is exhibited in all Bilaterians—but not in most other multicells—because it is an anti-cancer adaptation. To my knowledge no journal has published any support for that proposal but the New York Times has reported that Dr. Norman Sharpless of the University of North Carolina reached the identical conclusion: “I don’t think aging is a random process—it’s an anticancer program … .”

If Dr. Sharpless and I are correct then it is wrong to presume that simple cell colonies like Hydra “control” senescence. They have never experienced senescence for the same reason they display no historical evidence of radiation avoidance: they have no evolutionary history of encountering lethal cancer. 

In my opinion it is as incorrect to assume senescence is experienced by all multicells (3) as it is to assume that they are all capable of cancer death.

Conclusion. At the time (1969) Gateff and Schneiderman reported lethal neoplasia in Drosophila there existed at the Smithsonian Institution in Washington D.C. the Registry of Tumors in Lower Animals which had been established in conjunction with the National Cancer Institute.  In his introduction to Monograph 31 "Neoplasms and Related Disorders of Invertebrate and Lower Vertebrate Animals" John C. Harshbarger, Director of the Registry, explained that the Registry served not only to collect specimens of possible neoplasms but to evaluate them. If problematic specimens were submitted the Registry would solicit diagnostic opinions from other scientists including "experts on neoplasia."

Unfortunately the Registry no longer exists, and I do not know if any third party professionals will now evaluate the Hydra claim. But for what it is worth, in this non-expert amateur's opinion, the absence of lethality strongly suggests that classifying the phenomenon in Hydra as cancer is not justified.

Moreover, as an evolutionary theorist I consider the following characteristics of Hydra strongly suggestive of a cancer-free history: their tolerance of radiation, their freakish regeneration ability (4), individual specimen's "immortality" and—because my theory proposes (see the opening paragraph of my 1983 Letter) that intense selection pressure for the accumulation of cancer defenses enabled the Bilateria, and only the Bilateria, to produce multicells possessing spectacularly complex and efficient vital organs—their relative organismic simplicity.  

Notes

(1) Nat Cancer Inst Monogr 31: 365-397,1969.

(2) Research confirmed my initial reaction. Crown gall disease is initiated by bacteria, agrobacterium tumefaciens.

(3) As noted on pp 77-78 of Cancer Selection the world champions of longevity are all non-Bilaterians. Some trees (redwoods, sequoias, white oaks) live for centuries and Bonner has described a specimen of huckleberry with an estimated age of 13,000 years. Hydra are not the only cnidarians exhibiting "immortality." In the Victorian era some families kept sea anemones alive in their parlors for ninety years, death occurring only when someone knocked over the glass vessels in which they thrived.  

(4)  The astonishment of 18th century Swiss zoologist Abraham Trembley is apparent from this quotation: "I cut off the heads of the one that had seven, and after a few days I saw in it a prodigy scarcely inferior to the fabulous Hydre of Lernaea. It acquired seven new heads...But here is something more than the legend dared to invent: the seven heads that I cut off from this Hydre, after being fed, became perfect animals..."

Comments and questions are welcomed here.

At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and  the 1992 Nature review of my book.

 Copyright © 2014 by James Graham

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 © 2014 by James Graham

 © 2014 by James Graham