Hybrid lizards with introgressed mtDNA show increased resistance to DNA damage from Reactive Oxygen Species

Hybrids can experience genetic incompatibilities that lead to cellular
dysfunction and infertility. Previous analyses of mitochondrial function
in the lizards Urosaurus graciosus and Urosaurus ornatus found that
hybrids, which had introgressed mtDNA, experienced higher ATP production
which increases reactive oxygen species (ROS) production, one of the main
causes of damage to DNA. Hybrid populations of these lizards have
persisted so we predicted they may have mechanisms for protecting their
DNA from damage. To test this, we exposed liver cells of these lizards to
hydrogen peroxide, a source of ROS, and compared DNA damage using
single-cell gel electrophoresis. Hybrid cells showed significantly less
DNA damage. We then examined potential mechanisms to explain this result
by comparing melanin content of livers and expression levels of
antioxidant genes. If functioning to deal with ROS, these should be
expressed higher in hybrids. Melanin content of livers was highly variable
among U. graciosus individuals and therefore not highest in hybrids as
expected. Eighteen antioxidant genes showed significant differential
expression but were not expressed consistently higher in hybrids. The
overall gene expression profiles of hybrids and U. graciosus were very
similar while that of the mtDNA donor species, U. ornatus, was highly
divergent from both. Three antioxidant genes with different expression
levels in hybrids and that warrant further study were SOD2, SOD3, and
PRDX2. These results show how species can compensate for mtDNA
introgression and highlight the complexity of genetic interactions
encountered when closely related species exchange genetic material in
zones of secondary contact.