Chromosomal inversions have been identified in many natural populations
and can be responsible for novel traits and fast adaptation. In zebra
finch, an inversion in the Z chromosome has a pleiotropic effect on
multiple traits but especially on sperm. Males heterokaryotypic for the
inversion have sperm with a longer midpiece and higher velocity. They
have higher fertility and siring success than homokaryotypic males. To
understand the effect the Z inversion on these traits, we examined young
males at different stages of testis development using two homokaryotypic
lines and heterokaryotypes. We sampled both testis and liver tissue to
identify gene expression differences. In testis, 520 differentially
expressed genes were found and most of them were located on chromosome
Z. They were functionally enriched for sperm-related traits. In liver,
420 differentially expressed genes were not enriched for any specific
functions but showed also an overrepresentation on chromosome Z. In both
tissues, this overrepresentation was located near the distal end of Z
but also in the middle of the chromosome. For the heterokaryotype, we
observed several genes with expression patterns more similar to one or
the other karyotype, based on similarity to homokaryotype invidividuals.
This was confirmed with SNPs for three genes, and interestingly one
gene, dmgdh, had allele-specific expression originating from only one
inversion-allele in the testis, yet both inversion alleles were
expressed in the liver. This allele-specific difference in
tissue-specific expression demonstrates a pleiotropic effect of the
inversion and thus suggests a mechanism for divergent phenotypic effects
resulting from an inversion.