Wednesday, 23 October 2013

How did the spider cross New Zealand?

Questioning the distribution of animal species seems a bit pointless. All kinds of animals are in all kinds of places, for all kinds of reasons - who cares?

Biogeographers care. If you think about it, you can tell quite a lot about an animal's ecology, a country's geology, and evolutionary biology by looking at the distribution of species - not just the way they are today, but how their distribution has changed throughout time.

I'm interested in the biogeography (or phylogeography, which applies more to closely related species and individuals) of a genus of trapdoor spiders called Cantuaria. They're odd sorts, digging tunnels underground, living for a long time, and taking surprisingly good care of their offspring. Particularly interesting from a biogeographical point of view is the fact that, when the babies do decide to leave their mum at 6-8 months of age, they walk a few centimetres and then plonk themselves down, build a burrow and live there for the rest of their lives. Right next to their mothers' burrow. Maybe if it's a bit crowded, or there isn't enough food to go around, they might move a bit further but they are hardly aspiring adventurers. You certainly wouldn't expect them to travel vast distances across an ocean. It came as a surprise to me that they are distributed throughout New Zealand, from Stewart Island in the south right up to the North Island. The first thing I thought was that they must have been in New Zealand (or the mostly submerged continent of Zealandia, of which New Zealand is a small part) for a long time. That's ok, I thought, New Zealand has a lot of flightless ancient animals that were on Zealandia when it broke away from Australia. How else can you explain kiwi?

...except that it didn't. The traditional view that New Zealand's animals have been separated from Australia since the break-up of the supercontinent Gondwana falls apart with the addition of modern techniques. Molecular clocks, which tell us roughly when modern species started growing (diverging) out of ancestral species, show New Zealand's wildlife to be much newer than we thought. There is also evidence that it went through a bottleneck (a time when there weren't many individuals around) around the Oligocene, and that most, if not all, of Zealandia was under water during the Oligocene.

So my main question is how did trapdoor spiders cross New Zealand? How have such agoraphobic creatures spread themselves so far?

Most of the 42 Cantuaria species (reasonably numerous for a spider genus) are in the South Island, which is conveniently where I live. As well as using genetic study to see how many species there are, where they are and most importantly how they got there, I will study their lifestyle and relationship with their habitat and each other (in other words, their ecology). The ecological projects will help develop my understanding of Cantuaria phylogeography, but they will also contribute towards conserving Cantuaria and their natural habitat. Such unique and important creatures need to be preserved for the sake of future research, and for the sake of New Zealand's natural environment.

In a nutshell, that is my topic, the working title of which is "The phylogeography and conservation ecology of the trapdoor spider genus Cantuaria". I'll post more information on each individual project as I get into it a bit more.


  1. Very interesting, Vikki.. but work on flashing up that title!

  2. Thanks, it is purely functional right now so a bit dull. Suggestions welcome. Title of my proposal will be a bit flashier.