New Zealand has often been pictured as a kind of ‘ark’ of ancient species, isolated and unchanging since our land broke away from Gondwana 80 million years ago.
But new Royal Society of New Zealand Fellow Professor Jon Waters, over multiple Marsden Fund grants, has explored the idea that geology is both more and less important in our understanding of New Zealand’s biological diversity. He explains, with not-so-ancient freshwater fish, earthquakes that move rivers, and a spectacular diversity of flightless alpine stoneflies.
How has our thinking on the arrival of plants and animals in New Zealand changed?
For several decades it has often been assumed that a lot of New Zealand species were ancient relics. But now there’s wider acceptance for dispersal being a key force in New Zealand’s natural history. I work on our galaxiid fish, for instance, and at the moment we can’t see any indication that the ancestors of our current species were here before about 20 million years ago. These native fish represent an example of a group previously held up as ‘Gondwanan’, but now understood to have arrived by sea.
Looking at New Zealand’s geographic isolation from other landmasses, I was interested in how some of the species we share with other landmasses could move from one place to another. Some galaxiids spend up to six months at sea, and it’s not hard to see how they can get around. But a bunch of other groups I work on, including many marine invertebrates that brood their young, it’s less clear how they can disperse. I was interested arriving in Dunedin to see these huge buoyant kelp plants washing up on the beach at St Clair, with lots of invertebrate animals still living in their holdfasts. This was one of those moments when you know there’s something really worth looking into.
In the meantime we’ve been working on ancient DNA, using prehistoric specimens to assess changes in our coastal megfauna – penguins, seals and sea-lions. Again we’ve found that things are surprisingly dynamic, with species extinctions and replacements. Rapid change rather than stasis.
The debate about Gondwana and how things became distributed around is a complicated one because it’s an argument involving geology and biology. One of my views all along has been to try not to put the cart before the horse. The geological evidence should be assessed by geologists, the biological evidence by the biologists, and I feel it’s important to avoid circular logic – for example to base geological reconstructions on biological assumptions.
Long before anyone knew about continental drift, Darwin used to muse on species dispersal. Was he more right than we knew?
In explaining why some species are shared across isolated landmasses, Darwin didn’t talk much about kelp. He talked more about dispersal associated with iceberg movements and things like that. I think Darwin was amazingly observant in many ways, and some of his hypotheses are still coming true. In terms of animal dispersal, there are so many ways species can move, for example, by rafting across oceans on logs or on floating kelps. Even events that seem very unlikely can be possible given geological timeframes.
Then is geology less important than previously thought?
No, geology is still hugely important, and New Zealand is a fabulous place to study the biological effects of fast-changing geology. This is one of the world’s most geologically dynamic places, and biology changes fast as a result. We’ve got examples of tectonics where mountains are coming up that weren’t there only a million years before. In the past we had this idea of New Zealand having this static and unchanging biological history. But I think that’s changing as we use genetics and geology to understand the pace of evolution.
There’s been a lot of work on river reversal and capture, how catchments can change due to tectonics and glaciation. Research in New Zealand is telling us that geological uplift can isolate previously connected animal populations, and form new species – over short timeframes. This combination of genetics and geology has started to revolutionised our understanding of New Zealand’s biodiversity. As a result, we also recognise a wealth of diversity – one group of galaxiids we’ve worked on, previously thought to represent a single fish species, is now understood to be a complex of more than 10 species – our understanding has shifted fast.
I don’t think the argument was ever about geology versus biology. It was geology that brought New Zealand out of the water. But it is time to put the biology back in biogeography.
How did you get interested in river capture?
I was trying to build a family tree of species for the whole Southern Hemisphere, but some of the most exciting things I was finding were the finer-scale differences within and between individual river systems. I had never imagined I would start working with geologists, but sometimes when you talk to someone outside your field you make a lot more progress than talking to your immediate colleagues.
You’re now working with alpine insects. How does that fit in?
After all our work on freshwater fish, we were interested to expand to other freshwater species, so started looking at freshwater insects. One of the most interesting groups we’ve looked at are the stoneflies which spend most of their lives in freshwater, but emerge from streams as adults for a few days to breed (and then die). While most stonefly species fly as adults, many of New Zealand’s alpine species have lost that ability to fly. When we looked at some supposedly ‘widespread’ flightless New Zealand stoneflies, though, we realised they are actually very diverse, and it appears flight loss has happened a lot: perhaps each mountain has its own flightless lineage. But many of these flightless forms are closely related to other local stoneflies that do fly.
New Zealand’s alpine environment is quite new in geological terms (again, New Zealand is changing so fast) and our flightless alpine insects seem to have evolved very quickly in response to the rapid uplift. I was doing some work on the Rock and Pillar Range recently and, even though it is quite a nice day, it’s blowing about 100km/hour on the tops – you can easily understand why flying is not a good idea up there!
These interviews are supported by the Royal Society of New Zealand, which promotes, invests in and celebrates excellence in people and ideas, for the benefit of all New Zealanders.