Collier

Historical landscape influences on the genetic structure of fish and invertebrate populations in some New Zealand streams

Presented at Biodiversity Conservation in Freshwaters,
Fenner Conference on the Environment,
Canberra, July 2001.

K.J. Collier & R.M. Allibone

Understanding factors influencing the genetic structure of populations is important for successful biodiversity conservation. We have carried out isozyme electrophoresis studies of populations of the non-diadromous galaxiid fish Galaxias divergens Stokell and the hydropsychid caddisfly Orthopsyche fimbriata (McLachlan) in New Zealand streams to elucidate patterns in genetic structure and to provide insights into factors influencing observed patterns.

Seven polymorphic loci were used to distinguish among five genetic groups within G. divergens, with groups being determined by fixed allelic differences. The distribution of this species straddles the marine strait between the North and South Islands of New Zealand, and our results indicate that gene flow has occurred across this barrier more recently than among populations on the same landmasses.

Ten loci revealed non-fixed allelic differences among Orthopsyche populations north and south of the Auckland isthmus. The population structures of these two contrasting freshwater species appear to partly reflect historical events promoting or preventing gene flow.

These events may include (i) changes in sea-levels during glacial and inter-glacial periods that have periodically isolated areas of land, (ii) tectonic activity creating mountain ranges that may have formed dispersal barriers and led to the development of isolated populations, and (iii) volcanism which may have caused the possible elimination of populations in some areas.

Findings from these studies and elsewhere emphasise the importance of considering historical processes when defining landscape units for biodiversity management and conservation.