Relating gene flow to hydrology

Posted on December 15, 2011

Because the spatial separation of populations has a clear influence on connectivity and gene flow, isolation by distance can be a good indicator of population differentiation.  In river systems, connectivity is also affected by localised physical features such as waterfalls and weirs, and by the hierarchical branching patterns of streams.   By affecting the ease with which animals can move through river systems, it’s possible that large-scale variations in flow and other hydrological factors also affect connectivity.  Chinook salmon returning to the Yukon River to spawn migrate between 150 km and 3000+ km upstream, to natal populations situated in thirteen main drainage basins.  Different salmon populations were compared in terms of their genetic structure (microsatellite DNA profile), their relative location (waterway distance), and factors affecting hydrology (flow, elevation, gradient and the number of drainage basins passed by migrating salmon en route to the natal stream).  The results showed that although waterway distance was the most useful predictive factor , the largest amount of genetic variance (90%) was explained by a model that also included flow and basin number.  This finding is in line with other work on homing and straying in chinook, which found that fish showed more scent-based searching behaviour when the number of non-natal streams near the natal stream was high, and when the flow from tributories was low.  Isolation-by-distance models of gene flow might therefore be too simplistic to explain large-scale population differentiation in some riverine species, and might be usefully supplemented with information on hydrology.

Reference:  Olsen, J.B., Beacham, T.D., Wetklo, M., Seeb, L.W., Smith, C.T., Flannery, B.G. & Wenburg, J.K.  2010.  The influence of hydrology and waterway distance on population structure of Chinook salmon Oncorhynchus tshawytscha in a large river.  Journal of Fish Biology 76, 1128–1148.