Southeastern Fishes Council, Chattanooga, TN, Nov 2011.

Using GIS to predict population connectivity in southeastern USA rivers based on continental shelf width.

P.J. Unmack.

The phylogeography of coastal rivers is an important topic that so far largely remains under exploited in terms of its full research potential. Salt water acts as a strong barrier to obligate freshwater species. Salt water barriers are highly dynamic in that they are controlled by sea level changes and coastal geomorphology. As sea levels fall, barriers are removed as formerly isolated rivers may coalesce together and allow dispersal. Therefore, when sea level is lowered, there is greater potential for dispersal to occur. As sea level rises again, barriers reform, isolating the fauna of each now separate river basin. Changes in sea levels occur in cycles, and at least throughout Pleistocene have occurred every 100,000-150,000 years and are thought to be strongly influenced by Milankovitch Cycles. Here I use GIS to map continental shelf width and low sea level drainage patterns to establish some hypotheses that can be tested by phylogeographic data. Broad continental shelves should allow greater opportunities for populations to mix than narrow continental shelves, as there is more opportunity for rivers to coalesce and for fishes to move between coastal floodplains. From this we can predict that fish populations present in coastal rivers that are separated by similar continental shelf widths should have similar genetic divergences, and that those divergences should be greater in narrow shelves and lower in broader widths. By using GIS to quantify potential limitations to gene flow, specific regions and species can be targeted to allow these hypotheses to be broadly tested.