4.3 | Adherence to the stream hierarchy model
In stark contrast, the analyses of the Meramec River only dataset
revealed a spatial distribution of genetic diversity that is structured
in an upstream to downstream pattern that corresponds to the stream
hierarchy model. There was evidence of a strong correlation of genetic
differentiation with river distance (Figure 5B) that was further
supported by the pattern observed in the DAPC (Figure 4C) and the
pairwise FST values (Table S3B). There is greater
genetic diversity (Table 1C) observed in the Meramec River than in the
northern Volga River, which is best explained by differences among
individuals within populations (Table 2C). There were also fewer genetic
clusters observed (Figure 3C) suggesting greater connectivity among the
local populations.
The adherence to the stream hierarchy model observed in the Meramec
River only dataset suggests that habitat in the region remained
relatively undisturbed by the climatic changes of the Quaternary period.
The river valleys of the Ozark Plateau are older and entrenched, and
lack sedimentation levels found within the glacial drift plains in the
North (Forman et al. 1992; Galloway et al., 2011). The lotic habitat of
these rivers also contains nearly continuous suitable habitat for the
rainbow darter. Taking these factors together, the best explanation for
the pattern observed is that life history of E. caeruleum ,
including high site fidelity and diet preferences of the species, shaped
the spatial distribution of genetic diversity. Rainbow darters and their
preferred prey have a preference for fast-moving riffle habitats and are
less prevalent in deeper slow-moving pools (Hicks & Servos, 2017;
Mueller et al., 2020). Therefore, the riffle-run-pool structure of
streams may represent a permeable barrier to migratory movement further
contributing to the observed pattern.