The freshwater crayfish, or koura (Maori name), is a crustacean from the genus Paranephrops which is endemic to New Zealand. Koura are very important to the functioning of freshwater ecosystems as they recycle leftover materials through their scavenging, help filter fine sediments from the water and also act as an indicator species, signalling to scientists when conditions in a stream or pond are unfavourable.
Koura are currently officially recognised as two distinct species, the northern koura Paranephrops planifrons and the southern koura Paranephrops zealandicus. However, recent work in the field of molecular genetics has resulted in some illuminating insights into whether there is just two species, or maybe more!
Smita Apte and Graham Wallis from Otago University and Joshua Smith from NIWA collected mitochondrial DNA samples from 76 sites and 182 koura throughout New Zealand with the aim of investigating whether the Southern Alps and Cook Straight have any effect on the shaping of genetic structure within Paranephrops.
The mitochondrial DNA marker cytochrome oxidase subunit I was the marker used in the analysis. Sequencing and subsequent analysis actually showed three distinct koura lineages as opposed to the two species which are currently described. The southern koura was shown as being just one species while the northern koura was split into two distinct groups; koura in the North Island and Nelson and Marlborough region and koura on the southern West Coast and rest of the South Island. So, the Southern West Coast portion of the species believed to be P. planifrons is actually more closely related to P. zealandicus than the species it is currently classified as being a part of.
These results indicated that the the mountain building of the Southern Alps provided an important geographic barrier between the West Coast haplotypes and the Eastern South Island haplotypes so that speciation could occur. However, this is not over the whole of the Southern Alps range because koura on the outhern West Coast were found to be more genetically similar to the northern koura than the other West Coast haplotypes. This results in a threefold genetic structure, with a seperation essentially into northern, central and southern koura lineages.
This has some broad implications for the future conservation of the treasured koura in New Zealand. Koura are currently listed as threatened species and their populations are in gradual decline due to habitat destruction, predation by introduced species and over-harvesting by humans. With this genetic work uncovering three distinct genetic species, the classification of koura needs to be reconsidered to include these three species. Furthermore, conservation initiatives now need to consider three species instead of just two.
The original paper, which was published in Molecular Ecology, volume 16, pages 1897-1908, can be found here.
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ReplyDeleteHi Warwick, you state "koura on the Southern West Coast were found to be more genetically similar to the regular southern koura than the other West Coast haplotypes". I would highly recommend looking at the map in the article by Apte and Wallis. This clarified the geographic locations of the three lineages.
ReplyDeleteI have some questions from reading the blog. Has the presence of a hybrid zone been investigated between the distribution of the two lineages on the South Island west coast? Continuous sampling would answer this question. Is there a possibility that a similar pattern to the westland beech gap would be observed? This has the possibility of adding further evidence to the phylogeography study of the beech gap by Trewick and Wallis (which can be found in Evolution, Volume 55, Issue 11 (p 2170-2180)or at http://www3.interscience.wiley.com/cgi-bin/fulltext/118969755/PDFSTART
This blog really goes to show how important molecular techniques have been for species identification. It would be interesting to see what alterations have been made to the conservation of Koura as a result of this study.
ReplyDeleteOops my bad Ian. I actualy had P. planifrons as being the Southern crayfish and P. zealandicus as the Northern crayfish when it is in fact the other way around. That will have been what confused me as I took my statement from the text and not the figure. All fixed now. Cheers.
ReplyDeleteI couldn't find any information about a hybrid zone between the two/three species, it would be interesting to see if there is.
The pattern of the phylogenetic study of the crayfish does seem to support the idea of the beech gap being a possible cause for their divergence, but I don't know how the beech forest gap would affect the koura?