Data for: Sex, amitosis, and evolvability in the ciliate Tetrahymena thermophila

Understanding the mechanisms that generate genetic variation, and thus
contribute to the process of adaptation, is a major goal of evolutionary
biology. Mutation and genetic exchange have been well studied as
mechanisms to generate genetic variation. However, there are additional
factors, such as genome architecture, that may also impact the amount of
genetic variation in some populations, and the extent to which these
variation generating mechanisms are themselves shaped by natural selection
is still an open question. To test the effect of genome architecture on
the generation of genetic variation, and hence evolvability, we studied
Tetrahymena thermophila, a ciliate with an unusual genome structure and
mechanism of nuclear division, called amitosis, whereby homologous
chromosomes are randomly distributed to daughter cells. Amitosis leads to
genetic variation among the asexual descendants of a newly produced sexual
progeny because different progeny cells will contain different
combinations of parental alleles. We hypothesize that amitosis thus
increases the evolvability of newly produced sexual progeny relative to
their unmated parents and species that undergo mitosis. To test this
hypothesis, we used experimental evolution and simulations to compare the
rate of adaptation in T. thermophila populations founded by a single
sexual progeny to parental populations that had not had sex in many
generations. The populations founded by a sexual progeny adapted more
quickly than parental populations in both laboratory populations and
simulated populations. This suggests that the additional genetic variation
generated by amitosis of a heterozygote can increase the rate of
adaptation following sex and may help explain the evolutionary success of
the unusual genetic architecture of Tetrahymena and ciliates more
generally.