Influence of the mutation load on the genomic composition of hybrids
between outcrossing and self-fertilizing species
Abstract
Hybridization is a natural process whereby two diverging evolutionary
lineages reproduce and create offspring of mixed ancestry. Differences
in mating systems (e.g., self-fertilization and outcrossing) are
expected to affect the direction and extent of hybridization and
introgression in hybrid zones. Among other factors, selfers and
outcrossers are expected to differ in their mutation loads. This has
been studied both theoretically and empirically; however, conflicting
predictions have been made on the effects mutation loads of parental
species with different mating systems can have on the genomic
composition of hybrids. Here we develop a multi-locus, selective model
to study how the different mutation load built up in selfers and
outcrossers as a result of selective interference and homozygosity
impact the long-term genetic composition of hybrid populations. Notably,
our results emphasize that genes from the parental population with
lesser mutation load get rapidly over-represented in hybrid genomes,
regardless of the hybrids own mating system. When recombination tends to
be more important than mutation, outcrossers’ genomes tend to be of
higher quality and prevail. When recombination is small, however,
selfers’ genomes may reach higher quality than outcrossers’ genomes and
prevail. Taken together these results provide concrete insights into one
of the multiple factors influencing hybrid genome composition and
introgression patterns in hybrid zones with species containing species
with different mating systems.