Stenonema, Stenacron, and Maccaffertium are three closely related genera of mayflies commonly found across North America. There are currently 22 described species in Maccaffertium, 7 described species in Stenacron, and 1 described species in Stenonema. Their primarily aquatic life history, and sensitivity to aquatic pollutant make these organisms ideal water quality indicators. However, there is little morphological variation within these genera leading to difficulties in identifications. The classifications of many of the species within these genera have been changed multiple times and still little is known about the relationships with in these genera. In an attempt to resolve the phylogenetic relationships of Stenonema, Stenacron, and Maccaffertium, two Mitochondrial genes (Cytochrome oxidase subunit 1 (cox1), and 16s ribosomal RNA (rrnl)) and two Nuclear genes (Wingless (Wg), and Histone H3) were sequenced from 60 individuals from the three genera, and ten individuals from three outgroup genera (Pseudiron, Epeorus, and Heptagenia). Maximum likelihood and Bayesian analysis were conducted on single-gene and concatenated multi-gene data sets, and species tree methods were utilized to resolve the phylogenetic relationships. Molecular analysis resolve Maccaffertium as paraphyletic, with Stenonema femoratum being resolved within Maccaffertium, as sister to M. mexicanum integrum. Stenacron in most cases was also resolved within Maccaffertium, as a close relative of M. lenati. In order to achieve monophyly, Stenonema needs to be expanded to include Maccaffertium and Stenacron, and four subgenera should be erected to name the well supported clades; Stenonema, Maccaffertium, Stenacron, and Lewisa.

<p>Mayflies are important macroinvertebrate members of steam communities and are highly sensitive to agricultural insecticides. In this dissertation I sought to explore whether Heptageniidae<i> </i>mayflies in Indiana have evolved greater tolerance to clothianidin, a neonicotinoid insecticide that has been widely applied over the predominant corn and soybean crops of the state for the last 20 years. Over the five chapters of this dissertation, I investigate different aspects of the effects of clothianidin on mayfly populations. First, I collected mayfly populations from streams around the state across a gradient of agricultural landscape to see if proximity to corn and soybean crops was associated with tolerance to the insecticide. I found significant variation in tolerance between the populations but only connected it to land use for one species and one insecticide. Second, I investigated the potential for increases in predation rates due to exposure to low concentrations of clothianidin by both a vertebrate and invertebrate predator. Sublethal exposure did increase the risk of predation by the invertebrate predator but not the vertebrate. Third, I collected four populations of mayflies and placed them in a common stream which is heavily impacted by agricultural runoff. The most tolerant of the four populations had the highest survival rates and was native to the polluted stream, suggesting that it was best adapted to the local conditions. Finally, the last chapter is a discussion of the factors influencing the evolution of contaminant tolerance, the implications for biomonitoring, and a series of recommendations for incorporating evolved tolerance into biomonitoring practices. Collectively, this work suggests that the lethal and sublethal effects of clothianidin exposure create conditions suitable for the evolution of tolerance in Heptageniid mayflies. While there are already differences in tolerance between populations, it seems likely that mayfly pesticide tolerance will continue to increase as pesticides continue to impact aquatic ecosystems. </p>