Gondwana origin for subantarctic beetles
Scientists have identified two new beetle species on New Zealand’s subantarctic islands and three new beetle species on the Chatham Islands.
But they still haven’t resolved whether these insects originated recently or are much older and from Gondwana, the ancient supercontinent that once existed at the bottom of the world.
If so, these beetles would have quietly persisted on these remote islands for more than 80 million years.
‘‘The jury is still out,’’ Dr Richard Leschen, of Landcare Research, said.
What is today New Zealand and the subantarctic islands group split from Gondwana about 80 million years ago and slowly drifted away from what is now Australia and Antarctica.
Little is known about the subantarctic islands after the split until more recent times.
These gaps in the geologic record might be filled with biological information, which is why subantarctic species like beetles attract attention from researchers.
If these beetles originated in Gondwana and lived in isolation for 80 million years, then scientists would expect to see unique evolutionary adaptations.
There are differences, according to Brittany Owens, the Louisiana taxonomist who identified the five new species in a September article in the journal Insect Systematics and Diversity.
She identified differences in one species that may be adaptations to ‘‘feeding in harsh subantarctic island climates’’, as well as a ‘‘combination of unusual features and exaggerated morphology’’ in another species that suggests evolutionary adaptations to an extreme environment.
However, lots of other factors play roles in adaptation. In one beetle species, for example, Owens and Leschen found adaptations to body forms only in males, which are probably linked to sexual selection.
There are several other possible origins for these subantarctic beetles. One is that the Auckland, Campbell and other islands 500 kilometres to 600km south of Invercargill may have been joined to mainland New Zealand about 20 million years ago, Leschen said.
The islands later separated from the mainland, taking the beetles with them.
Another is that the beetles flew, or were blown, to the islands. Or were rafted there by a tsunami or other oceanic event, he said.
Another is that these beetles are circumpolar and circle Antarctica rather than originating in warmer climates.
It is also possible that all of these routes were taken by the beetles – always there, flown, rafted and so forth, and arrived multiple times millions of years apart.
Owens identified three new beetle species on the Chathams, as well as one that is Australian in origin and widespread on mainland New Zealand.
But the Chathams are relatively young. Some volcanic islands there are thought to be
4 million to 7 million years old, while other island components are thought to be 1 million to
3 million years old.
There is also evidence of land bridge between the Chathams and mainland New Zealand.
In any event, the Chathams are generally downwind from the mainland and most species there are linked to relatively recent dispersals from New Zealand and before that probably Gondwana, Leschen said. The subantarctic islands are hard and expensive to reach, and researchers tend to focus on what’s easiest to collect and most common.
It’s the outliers that give the best clues about New Zealand’s ancient origins, Leschen said. He’ll just have to go back and look.