It is widely accepted that kopi (Corynocarpus laevigatus) is not native to the Chatham Islands but was brought to the islands by the ancestors of the Moriori to provide a food source. Since then kopi has become a spiritually significant tree, and in some respects almost as much of a totem symbol of the islands as hakapiri / akeake (Olearia traversiorum), kopakopa / Chatham Island forget-me-not (Myosotidium hortensia) and the black robin.
During 2009 a team headed by Dr Lara Shepherd (now of Te Papa Tongarewa, Museum of New Zealand) decided to study kopi (also known as karaka in New Zealand) to see where the tree was first domesticated. The then current wisdom suggested kopi is indigenous to the northern part of the North Island, all other occurrences in New Zealand, The Kermadecs and Chatham Islands stemming from deliberate plantings.
To resolve this matter is not easy. Kopi can start fruiting within five years of planting. So tree’s grow fast. Unhelpfully they don’t produce growth rings, so you can’t core tree’s and age them by counting rings. The tree’s produce very little pollen, and it is very rarely found in the pollen record – so taking peat and soil cores to look for pollen to date arrival doesn’t work either. The observation that fruit size is larger near old kainga and pa sites, so hinting at domestication has been established, but this doesn’t help source lineages. Further this is a fast-growing tree that has been moved around New Zealand an awful lot not only by Maori and Moriori but also more recently by European settlers. For all these reasons determining the source of domestication is not easy. So Lara’s team decided to look at using DNA.
Between 2009 and 2010 the team collected over 600 samples of kopi / karaka from throughout its known range, and these were then subjected to DNA analysis by looking at the genome of the tree. The DNA markers developed from that analysis found that trees from the Three King’s Islands and Northland’s Te Aupouri Peninsula were each genetically distinctive, so these two regions could be excluded as the source of cultivated kopi. Kopi from the rest of New Zealand (including the Chatham and Kermadec Islands) were so genetically similar that the origins of cultivated plants could not be further pinpointed using this method.
Research on the domestication of kopi continues. An initial screening of a few DNA chloroplast markers shows that Chatham Island kopi has only one of the six chloroplast variants found in the rest of New Zealand. Good news except that the chloroplast variant that was found in Chatham Island kopi is widespread throughout the North and South Islands so determining the New Zealand source from where kopi was taken to the Chatham Islands was not possible using that method.
Dr Shepherd is now trying to sequence the entire chloroplast region of kopi (that’s 160 000 base pairs of DNA!) from 96 different samples of karaka (including samples from the Chatham Islands). Right now the samples she has prepared have been submitted for sequencing. Hopefully these results will allow us to distinguish kopi / karaka from different parts of New Zealand. If so this should allow the sources of cultivated trees and their naturalizations to be determined. If this works, then Dr Shepherd will be analysing more samples with the aim to have all the results analysed and written up for publication.