Recombination rate variation and evolution

Abstract
Meiotic recombination is necessary for the proper segregation of chromosomes during meiosis, and in creating
genetic diversity in populations through the shuffling of alleles. Changes in the number of recombination events,
or recombination rate, can thus have impacts on individual organismal health via meiotic failure, and on
population fitness by influencing the efficacy of selection. And yet, variation in recombination rate has been
documented across the genome, and among populations and species. Despite progress in cataloguing
recombination rate variation, how and why recombination rate changes remains largely unknown. The goal of
my research program is to investigate the genetic and environmental causes of recombination rate variation, and
the consequences of recombination rate variation on genome evolution. Over the next five years, my lab will use
experimental evolution and genomics in Saccharomyces yeast to explore three main questions. First, how does
the recombination landscape change over short time scales? We are using whole genome sequencing to
construct genome wide recombination rates in multiple populations of Saccharomyces uvarum. We seek to
identify how the double strand breaks that initiate recombination are repaired as crossover or non-crossover
gene conversion events, and how these two types of events are conserved or divergent between populations.
This will be the first study to examine evolution in both types of recombination events in multiple populations,
offering an unprecedented view of the mechanism underlying recombination rate variation. Second, we are
investigating how adaptation to a new environment alters recombination rate. Recombination rate plasticity
has been linked to changes in temperature and other environmental factors for many years, but explicit tests of
environmental adaptation influencing recombination rate evolution (or vice versa) are missing. We will evolve
cold tolerant S. uvarum populations in the lab for increased thermotolerance, and use whole genome sequencing
to identify any shifts in recombination rate or the distribution of crossover and non-crossover gene conversion
events that occur as a result of adaptation to temperature. Finally, we’re exploring how recombination rate
influences the distribution and persistence of introgression in the genome following hybridization. We
are evolving admixed strains from 2 diverging populations of S. uvarum with partial reproductive isolation to test
the hypothesis that introgression is reduced in regions of low recombination due to selection against weak,
negative epistatic interactions. We’ll compare the distribution of introgression in evolved populations to
recombination maps to better understand what forces shape genomes in the generations after hybridization.
Overall, my research will leverage the benefits of working with the tractable Saccharomyces system to empirically
test longstanding hypotheses of how and why recombination changes over time.