The brothers, a tiny cluster of rocks in Cook Strait best known for their lighthouse, may contain New Zealand’s only population of a second species of tuatara.
This is the view of Dr Charles Daugherty, a senior lecturer in zoology at Wellington’s Victoria University and director of a group of scientists who have been studying natural populations of the unique reptile for the past four years.
The announcement follows blood protein analysis of tuatara from 24 of the 29 islands where the animals are known to occur. Blood samples were collected during a major tuatara survey carried out between November 1988 and April 1989, then analysed using similar techniques to those which give the ABO blood groupings in human beings.
Like lizards, tuatara have a large vein which runs down the length of the tail, and it was from this vessel that the sample was taken. The actual collection of blood required considerable patience. Because tuatara have a very slow heartbeat one to two beats per minute — blood tends to seep very slowly from the animals.
Results indicate that the Brothers’ population is genetically quite different from all other tuatara populations, and may therefore constitute a new species. Tuatara on nearby Stephens Island are also distinctive, but probably not sufficiently so to warrant species status.
At present all tuatara are classified under the name Sphenodon punctatus, though, ironically, the pioneer New Zealand naturalist W.L. Buller recognised that the Brothers tuatara were a separate species over a century ago, and called them Sphenodon guntheri.
Dr Daugherty hopes to resurrect the name once the present results are confirmed.
“What this analysis shows is that we have three separate varieties of tuatara in New Zealand,” says Dr Daugherty. “And given the importance of the reptile as an evolutionary relic, it is crucial that these populations be preserved.”
In external appearance all three groups are similar, but generally speaking the Brothers tuatara is smaller than the others and more brightly coloured, with olive skin tonings and dark brown spots.
The ancestry of the tuatara stretches back 200 million years, yet the animal seems to have changed little over that colossal timespan. The most recent fossils from the tuatara lineage, dated at 80 million years old, look almost identical to the present-day tuatara.
One thing that is known is that tuatara, like many native New Zealand birds, are vulnerable to introduced predators, particularly rats. Tuatara occur naturally on 24 islands between the Poor Knights and the Bay of Plenty, and on five islands in Cook Strait. Only seven of these islands are rat-free; on the others rats are clearly taking their toll. There have been two extinctions in the past 20 years, and the recent survey showed a marked absence of younger animals (indicating no successful reproduction) on islands where rats are present.
Stephens Island (rat-free) carries an estimated 50,000 tuatara; at the other extreme some islands have fewer than 30 adults. To ensure the preservation of the Brothers’ tuatara (present population: fewer than 400 adults), the Victoria University group plans to collect eggs from the islands in November, then hatch and maintain the offspring in captivity.
New Zealand Geographic will present a feature article on the tuatara in a future issue.