Collaborative Research: Unraveling the phylogenetic and evolutionary patterns of fragmented mitochondrial genomes in parasitic lice

Mitochondria are critical for the survival of organisms because they provide the energy necessary for cells to function. Because of their importance, even small changes to the mitochondria can have drastic consequences for the cell. This includes changes to the molecules (chromosomes) that contain genetic information in the mitochondria. Genetic information in the mitochondria is usually contained on a single, circular chromosome. However, chromosomes in the mitochondria of some species of lice (small, parasitic insects of mammals and birds) are separated onto several smaller, circular fragments. Fragmented chromosomes arose multiple times throughout the evolutionary history of lice, but are very rare and harmful in most other animals. Very little is known about how or why these fragmented chromosomes exist in lice. In this project, the researchers will seek to understand fragmented mitochondrial chromosomes by comparing genetic information from many different species of lice. The results from this research will provide insight into how cells work and could help scientists to better understand human mitochondrial diseases. The project will support multiple outreach opportunities in Arkansas, Indiana, and Illinois through the creation of displays and presentations at community STEM events. The project will also provide training for a postdoctoral researcher, graduate students, and undergraduate students working on the project, and for the broader research community through two workshops on analyzing mitochondrial genome data. The research will focus on three hypotheses related to fragmented mitochondrial genomes (mitogenomes) in lice: 1) non-functional, nuclear-encoded mitochondrial genes can result in fragmentation of the mitogenome, 2) fragmented mitogenomes allow for a reduction in purifying selection from mito-nuclear incompatibility, and 3) selection for a balanced number of mitochondrial gene copies can promote an increase in fragmentation. To test these hypotheses, the researchers will use whole genome sequence data to assemble mitogenomes and relevant nuclear genes from 444 species of lice that represent four distinct clades that have varying levels of mitogenome fragmentation. With these data, the researchers will then reconstruct the evolutionary history of mitogenome structure and compare genomic content in the four clades of lice. Specifically, the researchers will 1) estimate a phylogenomic trees to reconstruct the evolutionary patterns of mitochondrial fragmentation, 2) examine the absence of nuclear-encoded mitochondrial genes, 3) test for signatures of relaxed or positive selection, and 4) quantify the relative copy number of mitochondrial genes. This project is jointly funded by Systematics and Biodiversity Science and the Established Program to Stimulate Competitive Research (EPSCoR). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.