Negative epistasis: a route to intraspecific reproductive isolation in yeast?

Abstract

Exploring the molecular bases of intraspecific reproductive isolation captures the ongoing phenotypic consequences of genetic divergence and provides insights into the early onset of speciation. Recent species-wide surveys using natural populations of yeasts demonstrated that intrinsic post-zygotic reproductive isolation segregates readily within the same species, and revealed the multiplicity of the genetic mechanisms underlying such processes. These advances deepened our current understandings and opened further perspectives regarding the complete picture of molecular and evolutionary origins driving the onset of intraspecific reproductive isolation in yeasts.

Keywords: Epistatic interaction; Genetic incompatibility; Intraspecific diversity; Reproductive isolation; Saccharomyces cerevisiae; Yeast.

Figure 1. Negative epistasis segregates within populations of S. cerevisiae related to various environmental conditions

A. Distribution of epistasis cases according to various stress types. Shades of colors represent different conditions tested that belong to the same category. A total of 117 cases are categorized. B. Distribution of epistasis cases according to isolates crossed with S288c. Colors correspond to type of stress as indicated. Isolates are organized clockwise according to the level of sequence divergence compared to S288c, with CLIB192 being most closely related with a divergence of 0.11%.

Figure 2. The molecular basis of the first example of two loci Dobzhansky-Müller incompatibility related to respiration in S. cerevisiae

Crossing between isolate carrying allelic combination of a nonsense mutation and a tRNA nonsense suppressor with isolate without this combination. After meiosis, 25% of the offspring inheriting only the nonsense mutation but not the suppressor were non-viable on conditions with non-fermentable carbon sources, as the nonsense mutation was essential for respiration. Nevertheless, when the nonsense suppressor was introduced other genetic background, it could confer to gain or loss of fitness in different environmental conditions, possibly indicating an adaptive role of certain incompatible alleles in complex ecological contexts.