This project is funded by the National Science Foundation (U.S.A.; NSF grant # MCB-1817762) and is in the process of being transferred to Uppsala University as part of my hire as a Professor in the Department of Ecology and Genetics, Program in Evolutionary Biology at UU as on June 1, 2022. It aims to determine the evolutionary dynamics and sex-specific effects of mitonuclear interactions. In brief, four electron transport chain (ETC) mutations resulting in fitness reduction were generated in three sexual backgrounds of Caenorhabditis elegans. The sexual backgrounds include the facultatively outcrossing wildtype background, an obligately outcrossing fog-2 knockout, and an obligately selfing xol-1 knockout allowing us to determine the impacts of sexual systems on the dynamics of mitonuclear evolution. Experimental lines were evolved in large populations for 60 generations to allow spontaneous mutations that aid fitness recovery to arise in the presence of strong efficacy of natural selection. After sixty generations of population expansion, the experimental lines were sequenced on the Illumina Novaseq platform using paired-end sequencing. The primary scope of this project is to identify the spectrum of single nucleotide polymorphisms (SNPs), small insertions/deletions (indels) and copy-number/structural variant (CNVs/SVs) mutations accrued during fitness recovery and identify potential compensatory mutations that serve to ameliorate the deleterious consequences of the original ETC mutations.