Life with more than one genome

Thousands of species are currently polyploid, and contain multiple copies of their genome. On the other hand, the long-term establishment of organisms that have undergone ancient whole genome duplications (WGDs) has been exceedingly rare. The apparent paucity of ancient genome duplications and the existence of so many species that are currently polyploid provides a fascinating paradox. Interestingly, many ancient WGDs seem to have been established at very specific times in evolution, for instance during major ecological upheavals and periods of extinction. Our work has shown that WGDs observed for many different plant lineages seem to have coincided with the most recent major mass extinction, i.e. the K/Pg extinction, 66 million years ago. I will put forward different hypotheses of why polyploids, compared to their diploid progenitors, might have had some selective advantage that might explain their survival at times of extinction or environmental turmoil.  On the other hand, the duplication of entire genomes also greatly increases the genomic (and physical) complexity of gene regulatory and interaction networks. It is currently unclear how the increased complexity, modularity and redundancy of duplicated gene regulatory networks might affect polyploids.  Preliminary studies seem to suggest that more complex – e.g. more densely connected - duplicated networks might allow bigger and/or faster jumps in the fitness landscape, which might be advantageous in highly disturbed environments or during periods of environmental turmoil, while being disadvantageous in stable environments, where bigger ‘moves’ in the fitness landscape might be maladaptive or detrimental.