Animal movements between drainage basins: how random are they?

Posted on May 26, 2009

Geomorphological barriers between major freshwater systems mean that movements of stream fauna between adjacent drainage basins are impossible or very rare.  Mitochondrial sequence data have been used to look for evidence of genetic exchange across the barrier that separates the Lake Eyre and Gulf of Carpentariabasins.  Two species were studied: bony bream (Nematolosa erebi) and freshwater prawn (Macrobrachium australiense).  While there was no evidence that prawns had dispersed across the divide in the last million years, bony bream populations seem to have crossed at least twice, around 160,000 and 350,000 years ago.  These events occurred well after the Pliocene (5.5 – 3.3 million years ago), when geological activity connected and rearranged the two basins.  It seems that since the Pliocene faunal dispersal has occurred only very rarely, presumably assisted by low topography and large-scale flood events.  Why bony bream, but not freshwater prawns, managed to disperse, requires more explanation: was it just a random occurrence or can it be explained by biological (e.g., life history) differences between the species?

Reference:  Kate D. Masci, Mark Ponniah and Jane M. Hughes.  2008.  Patterns of connectivity between the Lake Eyre and Gulf drainages, Australia: a phylogeographic approach.   Marine and Freshwater Research, 59, 751-760.