Late Quaternary river drainage and fish evolution, Southland, New Zealand
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Craw, D and Burridge, CP and Anderson, L and Waters, JM, Late Quaternary river drainage and fish evolution, Southland, New Zealand, Geomorphology: An International Journal of Pure and Applied Geomorphology, 84, (1-2) pp. 98-110. ISSN 0169-555X (2007) [Refereed Article]
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Late Quaternary to Holocene landscape evolution in southern New Zealand was dominated by glacial outwash processes.
Evolution of the drainage network on a regional scale was punctuated by numerous river capture events associated with outwash
transport and deposition. River capture events can be inferred from geological and topographic observations throughout the region.
Independent evidence for river capture and drainage reorientation can be obtained from genetic studies of a freshwater-limited fish
(Galaxias ‘southern’, informal name). Regionally extensive interlinking of principal rivers (Mataura, Oreti, Aparima) via
coalescence of alluvial plains onshore, and offshore at sea level lowstands, has resulted in a widespread genetic homogenisation of
fish populations (b 0.9% mtDNA divergence). Genetically similar populations of G. ‘southern’ are present in an adjacent catchment
(Von) that was captured episodically by the neighbouring major river system (Clutha). The low degree of genetic divergence
between Oreti and Von catchments (b 0.15% mtDNA divergence) demonstrates that genetic interaction between fish populations
was severed recently, probably during the early Holocene. This is in accord with radiocarbon dating (11–13 ka) of the youngest
gravel level within the intervening divide. In contrast, morphologically similar fish in another adjacent major river (Waiau) have a
minimum mtDNA divergence of 2.4% from the fish in the Mataura, Oreti, and Aparima Rivers. This genetic separation occurred at
ca. 145–240 ka, based on the late Quaternary outwash terrace dating, in agreement with "molecular clock" estimates. Geological
and genetic data in combination provide powerful tools for the elucidation of local and regional geomorphic evolution where river
capture is an important process. The potential is strong for genetic data alone to provide information on the relative and absolute
timing of river capture events, but must be interpreted in the context of severance of water connections between catchments and
subsequent isolation of freshwater-limited populations.
© 2006 Elsevier B.V. All rights reserved.
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