4 | Discussion
The results of this study support the hypothesis that historical glacial
cycles during the Quaternary period influenced the observed genetic
signature of rainbow darter populations in drainages of central North
America. They support the prediction that populations in glaciated
drainages in the North do not fit expectations under the stream
hierarchy model, whereas populations in the unglaciated South do. The
pattern observed within the Volga River in the upper Mississippi River
basin reflects recurrent extirpation and recolonization of E.
caeruleum into the region caused by a disruption in the riverscape by
repeated glacial advance and retreat. In contrast, the pattern observed
within the Meramec River in the Ozark Plateau strongly adhered to the
stream hierarchy model. This region was not directly impacted by glacial
advances and the age and relative stability of the habitat and drainage
patterns allowed for populations of E. caeruleum to persist
uninterrupted. The observed genetic signature of the southern population
was shaped by the life history and habitat preferences of the species
rather than cycles of geologic and climatic disturbance.