<p> The central focus in evolutionary biology is understanding how environments influence population genetic diversity and divergence through both adaptive and non-adaptive processes. Using a population genomic approach to examine population structure and morphological divergence of black spotted topminnow fish allowed us to survey how populations vary in river environments. Fish throughout the river continuum occupy different habitats that vary in several environmental aspects such as water velocity, predators, prey, and spatial heterogeneity. Body shape and size are great features to focus on for identifying adaptations to local environmental pressures. Shape and size have effects on maneuverability and energy conservation and, due to this, are targets for selection to act upon. Populations in differing habitats have shown variation in body shape and size, although not all species show differences between habitat types, and some species do not show consistent changes in morphological characters.</p><p> A total of 283 fish were sampled from headwater and large river environments in the Gasconade (150 individuals) and Meramec (133 individuals) river systems during the summer months of 2013. Individuals were genotyped, and 5744 single nucleotide polymorphism (SNP) loci were used to analyze population structure. In general, the study supported divergence between the two drainages, but some evidence of mixed ancestry for individuals sampled in the large river environments suggesting incomplete lineage sorting or secondary contact. Substantially more genetic structure was observed in the Gasconade River samples when compared to the Meramec River samples. Headwater populations exhibited clear divergence from larger river populations. Headwater divergence could be attributed to smaller effective population sizes and greater susceptibility to genetic drift. </p><p> Adult individuals were subjected to geometric morphometric analysis. Of the 283 individuals sampled, 175 individuals were large enough for shape and size analysis. Centroid sizes (measure of overall size) confirmed that headwater fish from both river systems were larger than their downstream large river counterparts. As expected, most significant shape variation was found in the sexual dimorphism between males and females, where males have larger dorsal and anal fins than females. With sexual dimorphic characteristics factored out, Gasconade individuals exhibited deeper bodies than that of Meramec individuals, but Meramec fish exhibited longer caudal fins.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:1590884 |
| Date | 10 July 2015 |
| Creators | Westhafer, Eric Douglas |
| Publisher | Southern Illinois University at Edwardsville |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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