Chromosome Dynamics and the Evolution of Sex

We are developing the spectacular plant genus Oenothera (evening primrose) into a model system to answer fundamental questions about the evolutionary significance of chromosome recombination and segregation, as well as the roles of chromosome translocations and hybridization,respectively, in speciation. The ancestral state of this genus is sexual reproduction (outcrossing), however, ~30% of species have evolved a form of functional asexuality called Permanent Translocation Heterozygosity (PTH; see figure).

RecSegSexPTHMy recent postdoctoral work, with Stephen Wright and Marc Johnson at the University of Toronto, examined the consequences of repeated evolution of functional asexuality in the plant genus Oenothera. We analyzed a large RNAseq dataset from 30 Oenothera species, including within-species sampling, that encompasses 10 transitions between sexual reproduction and PTH (functional asexuality). Ongoing work in the Hollister lab will combine population genomics, transcriptome analysis, cytogenetics, and population modeling to address the following questions:

1. Does asexual reproduction reduce the efficacy of purifying selection on deleterious mutations? (Ref 14)

2. How do the timescales over which PTH has evolved compare with speciation times among sexual/PTH pairs? Was speciation concurrent with the evolution of PTH? Did PTH evolve by inter-specific hybridization, or within-species fixation of structural heterozygosity?

3. How do reciprocal translocations evolve within Oenothera populations? What are the population and molecular genetic factors underlying the high rate of translocations in this genus? How do the genes controlling crossing over and chromosome segregation differ among Oenothera species, and among genera in the Onagraceae?