The significance of past interdrainage connectivity for studies of diversity, distribution and movement of freshwater-limited taxa within a catchment

Aim: Historical connectivity between drainages may represent an underappreciated contributor to the biodiversity within a catchment. First, we tested whether an isolated population of freshwater-limited galaxiids represents a contribution by past interdrainage connectivity to this system’s biodiversity, rather than reflecting intracatchment dispersal or speciation. Second, we sought to distinguish between possible geomorphic processes that could have allowed any past connectivity. Location: The Clutha and adjacent Southland region drainages on the South Island of New Zealand. Methods: We estimated the phylogeographical relationships among 466 cytochrome b sequences from ‘roundhead’ Galaxias populations throughout the Southland region and the Clutha drainage, using three different methods. Subsequently, possible geomorphic mechanisms of interdrainage connectivity were examined concurrently with genetic population divergence time estimates obtained by coalescent analysis. Results: All sam...