Evolutionary Innovation by Polyploidy

TL;DR

This paper investigates how polyploidy influences evolutionary innovation, revealing that while it generally slows evolution, it can significantly accelerate adaptation across fitness valleys, with an optimal chromosome number identified.

Contribution

It introduces a simple model of polyploid cells, analyzes their evolutionary rates, and proposes an optimal chromosome number for innovation based on large deviation theory.

Findings

Polyploidy often slows evolution under neutral or gradual conditions.

Polyploidy can drastically increase evolution probability over fitness valleys.

An optimal chromosome number for evolutionary innovation was identified.

Abstract

The preferred conditions for evolutionary innovation is a fundamental question, but little is known, in part because the question involves rare events. We focused on the potential role of polyploidy in the evolution of novel traits. There are two hypotheses regarding the effects of polyploidy on evolution: Polyploidy reduces the effect of a single mutation and slows evolution. In contrast, the gene redundancy introduced by polyploidy will promote neofunctionalization and accelerate evolution. Does polyploidy speed up or slow down evolution? In this study, we proposed a simple model of polyploid cells and showed that the evolutionary rate of polyploids is similar to or much slower than that of haploids under neutral selection or during gradual evolution. However, on a fitness landscape where cells should jump over a lethal valley to increase their fitness, the probability of evolution in polyploidy could be drastically increased, and the optimal number of chromosomes was identified. We theoretically discussed the existence of this optimal chromosome number from the large deviation theory. Furthermore, we proposed that the optimization for achieving evolutionary innovation could determine the range of chromosome numbers in polyploid bacteria.