Science Centres: Aquatic Biodiversity and Biosecurity

DNA sequences in upland bullies show that fish from different catchments, while looking the same, have different DNA base composition.

Unlike some other bullies, upland bullies (Gobiomorphus breviceps, a native freshwater fish) don't disperse to sea. Being river-locked, there is less opportunity for genetic mixing between populations, so there are likely to be genetic differences between them.

To investigate this hypothesis, NIWA biologists compared mitochondrial DNA from 89 bullies collected from 19 catchments across their range. They found that fish from within a catchment are genetically similar, while those from different catchments are genetically distinct, despite looking much the same.

The most striking differences were between populations of bullies on either side of the Southern Alps, which date back to the uplift of the Alps 2-5 million years ago. These were greater than the differences between populations from the northwest of the South Island and the southern North Island, reflecting a time during the Pleistocene ice age when the two islands were connected.

"Nearly every catchment we went to had a genetically different population," says NIWA biologist Dr Peter Smith, who led the research. "In that respect, most catchments contain unique populations and are worth conserving."

NIWA scientists are now looking at other species including koura, mayflies, and caddisflies with a view to defining biogeographically distinct freshwater units. Both projects have been funded by the Foundation for Research, Science & Technology (FRST).