Tuatara: The Evolutionary Speed Demon

There is a paper out in Trends in Genetics reporting the results of a study on the molecular evolution of the tuatara (Sphenodon punctatus). By comparing DNA extracted from 8,000 year old tuatara bones with samples from modern specimens, they determined that the tuatara has the fastest molecular evolutionary rate of any species that has been analyzed so far. This is interesting and surprising, because morphologically they are very conserved. According one of the researchers, Dr. David Lambert (snipped from the Science Daily report):

"Of course we would have expected that the tuatara, which does everything slowly -- they grow slowly, reproduce slowly and have a very slow metabolism -- would have evolved slowly. In fact, at the DNA level, they evolve extremely quickly, which supports a hypothesis proposed by the evolutionary biologist Allan Wilson, who suggested that the rate of molecular evolution was uncoupled from the rate of morphological evolution."

Research results that overthrow previous assumptions are extremely important, it will be interesting to follow this story and see what the implications are for both future molecular evolution studies (it supports the idea that phenotypic and molecular change can be decoupled) and for Sphenodon conservation. The tuatara is extremely unique, it is the last remaining member of its entire order, Sphenodontia, which has a fossil record extending back into the Triassic. There are extant two species, S. punctatus and S. guntheri, both highly endangered and limited to New Zealand. They are perhaps most famous for their "third eye," which is a form of the pineal organ. This organ is present in various morphs among other vertebrates as well, some suggest that it is a feature basal to all chordates. It is thought to function mainly in regulating circadian rhythms and body temperature.

What does this high rate of molecular evolution mean for their potential survival? Does it explain why they have managed to adapt and persist for the past 200 million years, and will it be of any advantage in facing the looming changes of climate? This is definitely fascinating news, hopefully it will become an example of how molecular studies extend beyond the lab and help to improve knowledge essential to conservation.

HAY, J., SUBRAMANIAN, S., MILLAR, C., MOHANDESAN, E., LAMBERT, D. (2008). Rapid molecular evolution in a living fossil. Trends in Genetics, 24(3), 106-109. DOI: 10.1016/j.tig.2007.12.002

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