by Greg Mayer
Tuataras are very interesting animals: endemic to New Zealand, and the sole survivors of an ancient and once more widespread order of reptiles, the Sphenodontida, whose closest relatives are the squamates (lizards+snakes). I noted some of their distinctive traits in an earlier post. When a friend went to New Zealand for a visit during the holidays, I asked him to get a picture of a tuatara if one came his way, and he obliged.
Tuataras are also of interest with regard to the ” species problem”, which Jerry recently addressed with respect to how many species of elephants there are (with follow-ups here and here). Ernst Mayr defined species in 1942 as
Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such group.
This definition, known as the biological species concept, is the one Jerry argued in favor of in his posts (and more extensively in Speciation, his book with Allan Orr). Through most of the 20th century, a single geographically variable species of tuatara, Sphenodon punctatus, was recognized. In 1990, on the basis of morphological and, primarily, allozyme differences, Charles Daugherty and colleagues argued that a second species, S. guntheri, occurring on islands in eastern Cook Strait (see map), should be recognized. (Allozymes are proteins which are different alleles at the same genetic locus, and which are usually distinguished by protein electrophoresis.)
At the time, this bothered me, as I saw it as an application of the old morphological species concept, extended to genetic data: if you can tell them apart, they are different species. This is also what Jerry argued against in the case of elephants: an arbitrary amount of morphological or genetic difference, or inferred time of separation based on the amount of genetic difference, is not a sound basis for a species concept.
Recently (2010), however , further studies of tuataras have been made, including study of their DNA, and the authors of this work conclude that, as had been held earlier, a single geographically varying extant species of tuatara should be recognized (the status of the extinct tuataras from the New Zealand mainland is still up in the air). So we’re back to S. punctatus as the sole surviving species in the Sphenodontida.
This turnaround in tuatara taxonomy is also a nice example of something Jerry considered in a previous post: scientists changing their mind in the light of new evidence, and not being shy about saying so (something which, of course, should not be rare). Two of the authors of the 1990 resurrection of S. guntheri, Charles Daugherty and Jennifer Hay, are also authors of its 2010 sinking.
If you would like to sample more things tuatara, Hillary Miller, a post-doc at the Allan Wilson Centre for Molecular Ecology & Evolution in New Zealand, has been running, unbeknownst to me at the time of my initial post, an interesting series of posts on tuataras at her blog, The Chicken or the Egg. (Allan Wilson a New Zealander who was a graduate student and later professor at Berkeley, was a pioneer in the application of biochemistry to evolutionary questions.) See also Victoria University of Wellington’s Tuatara Biology page.
Daugherty, C.H., A. Cree, J.M. Hay & M.B. Thompson. 1990. Neglected taxonomy and continuing extinctions of tuatara (Sphenodon). Nature 347:177-179. (abstract)
Hay, J.M., S. D. Sarre, D.M. Lambert, F.W. Allendorf & C.H. Daugherty. 2010. Genetic diversity and taxonomy: a reassessment of species designation in tuatara (Sphenodon: Reptilia). Conservation Genetics 11:1063-1081. (abstract)