Mixing of genetic material from previously separated gene pools may
cause evolutionary change and hybrid speciation. This has been mostly
explained through interactions of existing genetic traits. In contrast,
evolutionary novelty through new mutations after admixture is less
explored. Herein, we tested the hypothesis that structural mutations
accumulate in invasive Cottus, an evolutionary young fish of hybrid
origin, relative to both parental species Cottus rhenanus and Cottus
perifretum. Among 10,979 genes screened for CNVs using comparative
hybridization arrays, 25 genes showed significant changes in copy number
in a natural population of invasive Cottus. Three genes with the most
pronounced increase in copy number were previously found to be
upregulated in invasive Cottus, suggesting potentially adaptive gene
dosage effects. Transposable element copy number was estimated by
mapping whole-genome sequencing reads against a de novo genome assembly
of transposable elements. We found a significant copy number increase in
20.7% of all putative transposable elements in invasive Cottus, compared
to a very rare decrease (0.01%) of TE copies relative to the parent
species. The possibility of rapid evolution of de novo copy number
variants was tested in laboratory crosses between the parental species.
F2 individuals of two families (C. rhenanus x C. perifretum) were
screened for de novo copy number changes of three candidate genes and
two transposons using digital droplet PCR. Although our results do not
support high rates new structural mutations they nonetheless show that
structural mutations accumulate after admixture and that copy number
increases of protein coding genes can manifest phenotypically in an
evolutionary young hybrid species. This supports the idea that
structural variants contribute to rapid evolution of admixed lineages.