Date/Time
Date(s) - 27/02/2025
2:30 pm - 3:30 pm

Speaker: Dr. Marwa Tuffaha (York University)
Dr. Marwa Tuffaha is currently a postdoctoral researcher at York University. Her recent research focuses on population genetics and infectious disease modeling.

Location: Hamilton Hall, Room 410 & Zoom

Title: Mutational Bias Shifts and Severe Environmental Stress Promote Mutator Emergence

Abstract: Elevations in mutation rates, also known as the rise of mutators, can be influenced by two main factors: mutational biases and harsh environmental challenges. We show that shifts in mutational biases—especially reductions or reversals—can increase an organism’s access to previously under-sampled mutations, resulting in higher frequencies of beneficial de novo mutations. Through a discrete-time mathematical model and simulations, we demonstrate that this enhanced access facilitates the rise of mutator strains with larger fitness effects. We also consider how evolutionary rescue can promote mutator lineages under abrupt or gradual environmental stress. Using branching processes and deterministic models, supported by simulations, we show that de novo mutators are likely to hitchhike due to evolutionary rescue events when the wildtype mutation rate is intermediate, while pre-existing mutators in the populations have a significant advantage when mutation costs are minimal due to low wildtype mutation rates. Unsurprisingly, the stronger a mutator is, the more effective it is if the wildtype mutation rate is low, while its relative advantage decreases in populations where the wildtype itself is a mutator. These findings underscore the important role that mutational biases and severe environmental stresses play in mutator emergence in asexual organisms and highlight mechanisms of adaptive evolution and drug resistance development.