Impacts of temperature on recombination rate and meiotic success in thermotolerant and cold-tolerant yeast species.

Meiosis is required for the formation of gametes in all sexually reproducing species and the process is well conserved across the tree of life. However, meiosis is sensitive to a variety of external factors, which can impact chromosome pairing, recombination, and fertility. For example, the optimal temperature for successful meiosis varies between species of plants and animals. This suggests that meiosis is temperature sensitive, and that natural selection may act on variation in meiotic success as organisms adapt to different environmental conditions. To understand how temperature alters the successful completion of meiosis, we utilized two species of the budding yeast Saccharomyces with different temperature preferences: thermotolerant Saccharomyces cerevisiae and cold-tolerant Saccharomyces uvarum. We surveyed three metrics of meiosis: sporulation efficiency, spore viability, and recombination rate in multiple strains of each species. As per our predictions, the proportion of cells that complete meiosis and form spores is temperature sensitive, with thermotolerant S. cerevisiae having a higher temperature threshold for completion of meiosis than cold-tolerant S. uvarum. We confirmed previous observations that S. cerevisiae recombination rate varies between strains and across genomic regions, and add new results that S. uvarum has comparably high recombination rates. We find significant recombination rate plasticity due to temperature in S. cerevisiae and S. uvarum, in agreement with studies in animals and plants. Overall, these results suggest that meiotic thermal sensitivity is associated with organismal thermal tolerance and may even result in temporal reproductive isolation as populations diverge in thermal profiles.