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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.
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