Insect Mitochondrial Genomics

The mitochondria (mt) is the primary energy producing organelle of animals. Mt are descended from bacteria which entered into a symbiotic relationship with the earliest eukaryotes and retains a degenerate, bacteria-like genome. The mt genome in animals consists of just 37 genes, 13 protein coding genes, 22 transfer RNA genes and 2 ribosomal RNA genes, as well as a regulatory element referred to as the Control Region. The arrangement of genes in the mt genome has been found to be generally conservative across higher taxonomic groups but vary considerably between groups. Insects are an exception to this rule in that several insect orders are highly variable in their gene orders – Phthiraptera (lice), Thysanoptera (thrips), Psocoptera (bark lice) and Hymenoptera (wasps). We are investigating the evolution of the mitochondrial genome in insects to determine the phylogenetic usefulness of gene arrangement data and total genome sequences. Specifically we have 4 projects going at this time:

1. Mt genome diversity in insects
To date total genomes have been published for only 10 of the 30 insect orders. We aim to sequence at least a single species from each order and several species from larger orders. This work is well advanced and we have to date sequenced an additional 40 species representing 17 additional insect orders; partial genomes have been determined for the remaining orders. The major aim of this project is to examine if genome sequence data is capable of resolving insect interordinal phylogeny.

2. Population effects on insect mt genomes
We are examining what drives the fixation of novel genome arrangements in insects by investigating if genetic drift is a factor. Three of the orders with the highest levels of genome diversity, lice, thrips and wasps, are parasites and have highly fragmented population generally of very low numbers. Genetic theory predicts that neutral and nearly-neutral mutations will accumulate faster in small populations due to higher drift pressures. We are examining groups of insects with small populations (parasites, glacial specialists, cave dwellers) to see if they have higher levels of genome diversity.
**This project is a collaboration with Dale Clayton (University of Utah) and Kevin Johnson (Illinois Natural History Survey).

3. Genome diversity in beetles (Coleoptera)
Beetles are the largest insect group and the most diverse group of life on the planet. The higher relationships of beetles have been notoriously hard to resolve and several of the standard genetic markers such as 18S rRNA genes fail to recover a monophyletic Coleoptera. Initial findings with mt genome sequence are showing that this marker might overcome the limitations of other nuclear markers. Additionally, we are finding that tRNA arrangements in beetles are more variable than previously thought. We are sequencing a wide variety of beetles to see if mt genome sequence data is useful in resolving the phylogeny of the group and also to see if tRNA arrangement can be used to group certain families together.
**This project is a collaboration with Kelly Miller (BYU) and is being undertaken by an undergraduate researcher Jaron Sullivan.

4. Metabolic effects on mt genome evolution in Orthoptera
The mitochondrion is the site of oxidative respiration and the intermediates produced in this process are highly destructive to mtDNA. We are interested in seeing if levels of substitutions, nucleotide composition, codon biases and other measures of genome structure vary in response to differences in metabolism level between insect species. Orthoptera (grasshoppers and crickets) are an ideal group to study in this regard as a wide variety of activity levels (a general indicator of metabolic rate) can be found in the group and furthermore there have been repeated transitions from active to sedentary lifestyles and vice versa. This allows many pairs of groups to be examined to see if changing life style has had an effect on rates of evolution within the mt genome.