Panagrolaimus Mitochondrial Genome Evolution: Impact of Reproductive Mode Samantha C. Lewis ♦ Dr. Dee Denver Zoology Dept. ♦ Center for Genome Research and Biocomputing

Background Recombination: a force at the population, organismal and molecular levels Gonochorists and parthenogens (Sexual species and asexual species) ∞ MUTATION

Background Theory: asexual organisms do not persist as long as sexual ones “Mutational Meltdown” Can reduced selection efficiency be observed at the molecular level?

Hypothesis Inefficient selection may be observed as non-synonymous protein-coding gene changes that lead to deleterious mutation These changes may be observed in the mitochondrial genome

Methods Sequence the mitochondrial genomes of one sexual and one asexual organism; compare Extract DNA from nematodes Sequence amplified products products Amplify mtDNA Perform DNA sequence alignments Genome content comparisons Analysis in MEGA and DNAsp

nad2 tRNA Icob tRNA I ………….. tRNA F tRNA G tRNA R PS 1579 AF 36 C. elegans AF36 sexual PS1579 asexual Gene rRNA No sequence tRNA Work to Date

Insertions; Deletions; Gene order Ka/Ks ratio  An index of selection efficiency  The lower the ratio, the stronger selection is Genome Comparisons Nucleotide diversity  A measure of genetic diversity  Highest in sexual species Homopolymer repeats

Insertions; Deletions; Gene order Ka/Ks ratio Theory Nucleotide diversity Homopolymer repeats Similar to C. elegans Higher in asexual Lower in sexual Higher in sexual Lower in asexual Higher in asexual Lower in sexual

Results AF36 - sexual PS asexual Homopolymers cause slipped strand mispairing during DNA replication Number of Repeats Length of Repeats (bp) Considerably more mononucleotide runs were observed in the asexual strain

Results PI-P PI-G PII-P* PI-P PI-G PII-P* LabelReproductive Mode PI-PPanagrolaimus Parthenogens PI-GPanagrolaimus Gonochorists PII-P*Other Nematode Parthenogens Sexual Panagrolaimus did show higher nucleotide diversity values Asexual Panagrolaimus did not show higher Ka/Ks values [Nucleotide diversity] [Ka/Ks]

Theory Support

Insertions; Deletions; Gene order Theory Support Similar to C. elegans

Insertions; Deletions; Gene order Theory Support Nucleotide diversity Similar to C. elegans Higher in sexual Lower in asexual

Insertions; Deletions; Gene order Theory Support Nucleotide diversity Homopolymer repeats Similar to C. elegans Higher in sexual Lower in asexual Higher in asexual Lower in sexual

Insertions; Deletions; Gene order Ka/Ks ratio Theory Support Nucleotide diversity Homopolymer repeats Similar to C. elegans Higher in asexual Lower in sexual Higher in sexual Lower in asexual Higher in asexual Lower in sexual

Conclusions Panagrolaimus is a superb model to study the evolutionary causes and consequences of transitions to asexuality in animals While some analyses were consistent with a reduced efficiency of natural selection in asexual species, others were not Further studies with expanded data sets are needed

Confirm presence/absence of Arg tRNA in mt genome Sequence more genes from Panagrolaimus and other nematodes – add to Ka/Ks analysis Apply genome scale technologies to the Panagrolaimus system – high-throughput sequencing Future Work

Acknowledgments The Denver lab: Dee, Dana, Bobby, Leslie, Steph, Caroline, Peter, Larry, Ashley Dr. Kevin Ahern Howard Hughes Medical Institute We thank many individuals for providing Panagrolaimus strains: James Baldwin (UC-Riverside, USA) ♦ Ann Burnell (National University of Ireland Maynooth) ♦ Marie-Anne Felix (Institut Jacques Monod, France) Einhard Schierenberg (Universität Köln, Germany) Paul Sternberg (Caltech, USA) ♦ the Caenorhabditis Genetics Center (University of Minnesota, USA)

nad2 tRNA Icob tRNA I ………….. tRNA F tRNA G tRNA R PS 1579 AF 36 C. elegans AF36 sexual PS1579 asexual Gene rRNA No sequence tRNA Work to Date OLD FIGURE!!!!!!!!!!!!!!!!!