Rock wren population structure within an alpine archipelago

[Michael Szabo]

"Naturally subdivided populations such as those occupying high-altitude habitat patches of the ‘alpine archipelago’ can provide significant insight into past biogeographical change and serve as useful models for predicting future responses to anthropogenic climate change. Among New Zealand's alpine taxa, phylogenetic studies support two major radiations: the first correlating with geological forces (Pliocene uplift) and the second with climatic processes (Pleistocene glaciations). The rock wren (Xenicus gilviventris) is a threatened alpine passerine belonging to the endemic New Zealand wren family (Acanthisittidae). Rock wren constitute a widespread, naturally fragmented population, occurring in patches of suitable habitat over c. 900 m in altitude throughout the length of the South Island, New Zealand. We investigated the relative role of historical geological versus climatic processes in shaping the genetic structure of rock wren (N = 134) throughout their range. Using microsatellites combined with nuclear and mtDNA sequence data, we identify a deep north–south divergence in rock wren (3.7 ± 0.5% at cytochrome b) consistent with the glacial refugia hypothesis whereby populations were restricted in isolated refugia during the Pleistocene c. 2 Ma. This is the first study of an alpine vertebrate to test and provide strong evidence for the glacial refugia hypothesis as an explanation for the low endemicity central zone known as the biotic ‘gap’ in the South Island of New Zealand."

http://onlinelibrary.wiley.com/doi/10.1 ... 9/abstract

[Jan]

I heard this author speak on the topic at the Birds NZ Dunedin conference. It is a fascinating study.
Unfortunately the author manged to slip our clutches a couple of times for a talk at Birds NZ Canterbury!
If you are around, author, and still available to speak, can you get in touch again?

[Nick Allen]

The subfossil evidence points to the Rock Wren being present at low altitudes before Kiore and other nasties arrived, so wonder if the researcher/s have factored this in - the Rock Wren seems to have an alpine distribution due to there being less introduced predator pressure there, like Kea (actually more a forest parrot that still lives close to sea level on parts of the West Coast and Nelson) and Takahe (that probably did better at low altitude but was only rediscovered in its last refuge among alpine tussock). Take away the predator pressure and I would expect that these species, and numerous others in NZ, would re-occupy the habitats, niches and distributions that introduced mammals have eaten or out-competed them out of, at least where the habitat is still available to them.

[Michael Szabo]

Yes, good point Nick. I wonder if any rock wren skins in museums originate from the alpine 'central zone'? If so, their DNA may provide further insight.

[Jan]

I don't think there are many, if any, Rock Wren skins in Museums. Canterbury has lots of Riflemen but Paul will know if there are any Rock Wren.

[Mandyjane]

I'm still trying to decipher the first paragraph - I understand (I think) the term low endemicity but what is the central zone and the biotic gap ? Is this saying that there is an area in NZ which has a low number of endemics and species in general ? And then why does the glacial refuge hypothesis support that ? Wouldnt it support more endemics by having multiple glacial refuges ?? I am probably being thick - just trying to get my head around it - thanks

[Ian Southey]

Mandyjane

The biotic gap is, I think, what we used to call the 'beech gap'. It is more or less the glaciated waist of the South Island. There are many endemic plants and animals in the northern and southern parts of the mountains but fewer there, rather a preponderance of wide ranging species.

A fairly common sense argument for this is that during the last ice age heavy ice cover and glaciers converging into moving sheets of ice over the lower country effectively sterilised whole the area and that most of the plants and animals now living there are widespread species that have colonised since the glaciers retreated. The idea is that there would have been two nuclei of Rock Wren populations, presumably somewhere in Nelson/Marlborough and Fiordland/Otago, that survived in some small corner but as the ice melted they were able to spread until they met in the middle - at Mt Cook.

For what its worth beech trees don't spread so well as they are limited by a need for symbiotic soil fungi which seem to just creep along really, really slowly so the theory is that 10,000 odd years has not been enough to let them get very far at all.

It's not the only explanation but probably the most popular and it may be right. I don't remember the alternatives well enough to make up a comprehensible story.

Michael - I saw this talk at an OSNZ AGM, Dunedin I think, and the really impressive thing was that it looked like Kerry must have climbed a hell of a lot of hills to gather all her samples so I suspect further genetic material from museum specimens won't add much. The genetic difference is big and quite sharp so that a taxonomic difference seems possible but I don't think morphology was examined at all. It might be worth spending time in the Mt Cook area where these two clades meet to see if two kinds of birds can be distinguished there ...

Ian

[Michael Szabo]

Yes, I think Kerry is organising some surveys at the moment so I'll suggest that to her, Ian.
Michael

[Jan]

If you are in touch with Kerry, Michael, maybe you could ask her to email Jan, RR of Birds NZ Canterbury, to see if we can arrange a talk next year sometime when she is visiting parents down here?

[Mandyjane]

Thanks Ian for the explanation... logical ...