Speaker
Description
Evolutionary biology studies populations of reproducing individuals and how their composition changes over time.
An important question is to determine the fixation probability of a single advantageous mutant that attempts to invade a homogeneous population of $N$ residents.
Many real populations experience gradients of chemicals or nutrients that cause mutations to be beneficial in some spatial regions and possibly harmful in others.
We study the fixation probability of a mutant placed on a simple one-dimensional spatial structure that experiences such a gradient.
The mutant's fitness varies linearly from $1-s$ to $1+s$, whereas the resident fitness is constant and equal to 1.
The existing literature suggests that such heterogeneity in mutant's fitness should lead to a decrease in its fixation probability.
However, in this work, we find that small, non-negligible gradients ($s<1/\sqrt{N}$) substantially increase the fixation probability, while too large gradients ($s>(\log N)/\sqrt N$) substantially decrease it.
Moreover, we quantify the strength of this phenomenon analytically and we precisely delimit the range of the gradients for which it occurs.
Computer simulations closely match those findings.
Our results indicate that subjecting a simple population structure to natural environmental conditions produces strong counterintuitive effects.
