22 September 2009

We are going to freeze dry you all!

Pereira, T., & Lopes-Cendes, I. (2009). Cryptic anhydrobiotic potential in man: Implications in medicine Medical Hypotheses, 73 (4), 506-507 DOI: 10.1016/j.mehy.2009.06.012

The Elsevier journal Medical Hypotheses has been in publication since 1975. I am not familiar with the journal's requirements for manuscripts, but judging from this particular paper, they don't appear to be stringent at all. I get the impression that if you include in your manuscript some buzz words and phrases, such as, "human genome", "positive selection", "applications in medicine" and "promising research field", you can get just about anything accepted for publication.

The hypothesis in this paper is that it is possible that "mammals and humans have a cryptic anhydrobiotic ability which has not been discovered yet because of an unknown specific pre-conditioning stage [that] is necessary."

The authors base this claim on the well known fact several groups of multicellular animals, for example, bdelloid rotifers, tardigrades, nematodes and arthropods, have representatives that can survive extreme desiccation for long periods. This penomenon is known as anhydrobiosis, or life in the absence of water. Therefore, the authors conclude that, because anhydrobiosis confers on an animal an "unprecedent [sic] advantage for life in several extreme and hostile conditions it would be expected that such [a] trait would be positively selected and kept during evolution. Thus, it is possible that anhydrobiosis is a widespread phenomenon but that has been observed only in a few species that naturally undergo desiccation."

Of the top of my head, I can think of 2 problems with this reasoning. First, anhydrobiotic survival is advantageous only if a species lives in a habitat that is periodically desiccated and if the species has no other means of surviving the dry period. With a few exceptions, anhydrobiosis is normally seen in microscopic animals. Larger animals deal with the drying of their habitats either by migrating to a wetter habitat or by preventing water loss from their bodies. So, for example, during the long, dry Mediterranean summers, slugs migrate deep into the soil where there is still enough moisture for them to survive, while the snails become dormant in their shells conserving water. Neither group displays the ability to undergo anhydrobiosis.

The second problem with the authors' reasoning is that it is highly unlikely that the ability to survive anhydrobiosis will be retained if there is no need for it. If a trait becomes unnecessary, it may persist, be lost or become a vestige (see, Lahti et al., 2009). An unnecessary trait will be retained if the benefits it confers outweigh the maintenance costs. Why would evolution maintain the ability to survive extreme desiccation in humans when they can simply migrate to a wet enough habitat?

But these problems don't stop the authors from speculating on the potential applications of anhydrobiosis in humans (somehow assuming that their hypothesis has been proven correct). This includes the storage of tissues and organs in a desiccated state, protection to [from] radiation and heat and, are you ready for this?, whole body conservation. Freeze dried humans for rehydration in the future? I think we've stepped over the boundary into silly science fiction.

This paper came to my attention because it cites one of my old papers on bdelloid rotifers (Örstan, 1995). They cite my paper to support their claim that metabolism stops during anhydrobiosis. It probably does, but the funny thing is that my paper was not about that.

Medical Hypotheses also needs a better copy editor.

David C. Lahti, Norman A. Johnson, Beverly C. Ajie, Sarah P. Otto, Andrew P. Hendry, Daniel T. Blumstein, Richard G. Coss, Kathleen Donohue, Susan A. Foster. 2009. Relaxed selection in the wild. Trends in Ecology & Evolution 24:487-496.

Örstan, A. 1995. Desiccation survival of the eggs of the rotifer
Adineta vaga (Davis, 1873). Hydrobiologia 313/314:373-375.

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