Hybridization, ancestral polymorphism, and cryptic species in Nothonotus darters (Teleostei: Percidae: Etheostomatinae)

Darters (Teleostei: Percidae: Etheostomatinae) are a diverse group of charismatic fish endemic to North America and many of their characteristics combined with the fact that diversity within the clade is relatively well known makes them an attractive system for studying evolutionary patterns. I used molecular and morphological data to identify patterns of hybridization in darters, introgression in Nothonotus darters, and small geographic scales of diversification in two Cumberland River drainage Nothonotus species. I compiled records of hybrid Etheostomatinae museum specimens and found that over one quarter of darter species were involved in hybrid specimens, species most frequently involved had large range sizes, and involvement was negatively correlated with phylogenetic distance.I created a Nothonotus phylogeny based on mitochondrial and nuclear DNA sequence data and morphological data, and the observed relationships were largely consistent with previous hypotheses; however, better resolution and sampling in this phylogeny identified novel relationships and paraphyly. I expanded genetic sampling of N. camurus, N. chlorobranchius, and N. rufilineatus, the three Nothonotus most frequently involved in hybrid specimens, to search for introgression. I found extensive mitochondrial replacement in N. rufilineatus, with those in the upper Tennessee River drainage having mitochondrial haplotypes similar to haplotypes observed in N. chlorobranchius and those in the Cumberland River drainage having mitochondrial haplotypes similar to haplotypes observed in N. camurus. Additionally, N. rufilineatus has acted as a 'conduit species' in the upper Tennessee River drainage by transferring N. chlorobranchius like haplotypes into N. camurus.I also expanded genetic sampling of N. microlepidus and N. sanguifluus, two Cumberland River drainage Nothonotus whose sister relationship had not previously been hypothesized, to identify the number of lineages within the Cumberland River drainage. I preformed Discriminant Analysis using meristic characters based on the lineages indicated by the genetic analyses and found that there were four distinct lineages. By comparing the diversity in these two 'species' to diversity in another subclade of darters, barcheeks, I concluded that the isolating mechanisms in the Cumberland River drainage occur at small geographic scales, as found in the barcheeks, have been persistent through significant evolutionary time, and across multiple darter subclades.