The Three Kings Islands is a small archipelago only 56 km off the northern tip of New Zealand. They are the sole emergent part of the Three Kings Ridge, the remnants of an island arc that formed during the break-up of East Gondwana. Some rocks have been dated to 19-22 million years ago but some people believe that the islands originated much earlier than that. It is uncertain how long the Three Kings Ridge has been isolated from the mainland but certainly for many millions of years! The very northern tip of New Zealand was probably an island as well at some stage in the ancient past, and is geologically more similar to the Three Kings than to the rest of New Zealand.
The Three Kings Islands host a large number of endemic species. For example, the beetle fauna is estimated to be 35% endemic and the terrestrial snail fauna is highly endemic. There are several endemic plant species including 12 trees and shrubs. What is intriguing is that the closest relatives of some of these Three Kings species are found not on mainland New Zealand but in New Caledonia, Australia, or elsewhere in the Pacific – extraordinary for a small group of islands within eyeshot of the coast of mainland New Zealand!
Thomas Buckley and Rich Leschen (Landcare Research, Auckland) have used comparative phylogenetic analysis to infer the age and biogeographic origins of insect fauna of the Three Kings Islands. They densely sampled six insect lineages (five beetle groups and one stick insect group) throughout New Zealand and sequenced mitochondrial DNA1 to assess phylogenetic relationships2 and determine the relative ages on the Three Kings Islands and mainland New Zealand lineages.
The analyses indicate that the Three Kings fauna have been long isolated from mainland New Zealand. Thomas and Rich recovered two biogeographic patterns:
- The first pattern was seen in three taxa, which had sister group relationships between the Three Kings and the adjacent Te Paki/North Cape area at the very northern tip of New Zealand.
- The second pattern, inferred in the other three taxa, had sister groups that were widespread throughout most or all of New Zealand.
These results are consistent with continual emergent land on the Three Kings Ridge since at least the Miocene and a lack of land connections between the Three Kings Islands and mainland New Zealand during Pleistocene sea-level lowering. Despite their narrow separation, westerly ocean currents may be limiting dispersal between the Three Kings Islands and mainland New Zealand.
The results further exemplify the biogeographic significance of the Three Kings biota. The high levels of genetic differentiation of insect populations on the Three Kings relative to the ‘sister’ populations from the mainland, coupled with a more ancient endemic element, exemplifies the importance of these islands for New Zealand biodiversity.
The research also highlights the importance of strengthening conservation measures to ensure the survival, integrity and recovery of the biota. The islands were occupied by early Māori. By the time Europeans arrived in mid seventeenth century, Manawatawhi was largely denuded of trees. But, following the eradication of goats in the1940’s, forest has begun to regenerate. Any active restoration and augmentation using species sourced from mainland New Zealand would requires detailed knowledge of both the biogeographic history of the islands and the phylogenetic distinctiveness of species populations to determine appropriate areas for sourcing related populations for translocation.
Buckley, T.R. and R.A.B. Leschen. 2012. Comparative phylogenetic analysis reveals old and recent lineages on the Three Kings Islands, New Zealand. Biological Journal of the Linnaean Society, in review
Footnote 1: Mitochondria are tiny organelles or structures inside a cell that help convert food energy into a form that cells can use. Although most DNA is packaged in chromosomes within the nucleus of a cell, the mitochondria also have a small amount of their own DNA.Because mitochondrial DNA is passed through the maternal line, it enables researchers to trace an organisms direct lineage back in time.
Footnote 2: A phylogeny depicts a pattern of descent. Traditional classification schemes were often based upon similar morphological characteristics that may or may not reflect descent, whereas phylogenies are based upon derived characters that are shared by all of the descendants from a common ancestor. Recent efforts to unravel the phylogenetic ‘tree of life’ utilize morphological, anatomical and molecular characters even entire genomes. Because of their predictive power, phylogenies are becoming more widely used in plant classification, biodiversity assessment and ecological studies of character evolution.