Does fish ecology predict dispersal across a river drainage divide?

Area of Science:

• Ecology
• Evolutionary Biology
• Genetics

Background:

• Freshwater taxa distributions are often shaped by catchment isolation due to marine and terrestrial barriers.
• Isolation can result from geological changes in river systems or dispersal through temporary freshwater links.

Purpose of the Study:

• To investigate interdrainage dispersal in freshwater fish between two adjacent river catchments in southern New Zealand.
• To determine if species' ecological traits influence their capacity for dispersal and genetic structuring.

Main Methods:

• Sequencing of mitochondrial DNA (cytochrome b and control region) from over 100 individuals per species across four distinct freshwater fish taxa.
• Phylogeographic analysis incorporating taxon-specific mutation rates and the age of the last riverine connection.
• Statistical phylogeography to assess population isolation and infer dispersal events.

Main Results:

• Phylogeographic patterns aligned with ecological expectations of dispersal ability.
• Obligate riverine taxa showed reciprocal monophyly between catchments, indicating isolation.
• Facultative swamp dwellers exhibited paraphyletic relationships, with one species sharing haplotypes between catchments, suggesting dispersal.
• Statistical analysis rejected complete isolation for one swamp-dwelling species, inferring dispersal across a young drainage divide.

Conclusions:

• Species ecology is a significant predictor of interdrainage dispersal capability in freshwater taxa.
• Dispersal across recent drainage divides can occur and influences contemporary genetic structure.
• Historical drainage geometry is crucial for understanding genetic structuring in freshwater populations.