Access Type

Open Access Dissertation

Date of Award

January 2020

Degree Type


Degree Name



Biological Sciences

First Advisor

Thomas Dowling


Round goby (Neogobius melanostomus) is an invasive fish present in all five Great Lakes and is becoming increasingly common in their tributaries. Johnny darter (Etheostoma nigrum) is a native species that often coexists with round goby. Here, I use traditional population genetic methods and genomic tools to explore the evolutionary ecology of these species. First, historic factors are addressed as a source of variation in study populations by characterizing patterns of mitochondrial DNA variation throughout Lower Michigan. Round goby populations were largely homogenous and exhibited no evidence of overarching historical genetic structure, consistent with the recent invasion and rapid expansion of this species. Johnny darter exhibited significant differentiation among local populations; however, similarity among mtDNA haplotypes indicated that differences among populations are recent. Therefore, historical factors should have limited influence on patterns of gene expression in study populations.

Response to environmental heterogeneity was assessed by comparing gene expression between these species. Differential expression analysis was applied to fishes sampled from two southeastern Michigan drainages, the Rouge and Clinton rivers, and gene expression profiles between the two drainages were found to be distinct for these species. Pairwise comparisons among sampling sites and years indicated that there were more differentially expressed genes in round goby than Johnny darter, suggesting that Johnny darter has a more specialized strategy while round goby exhibits more plasticity. Plasticity is often cited as a trait common to successful invaders and the ability to respond to a range of conditions may contribute to the rapid range expansion of round goby. Finally, co-expression analysis was used to identify groups of genes correlated with specific environmental factors for each species. The two species differ markedly in patterns of gene expression correlated to stressors, possibly reflecting round goby’s adaption to varying environmental conditions. An ability to more readily respond to environmental stressors may make round goby well-suited to degraded habitats, which are common sites of early invasion.