Hybridization increases mitochondrial production of reactive oxygen species in sunfish

Abstract

Mitochondrial dysfunction and oxidative stress have been suggested to be possible mechanisms underlying hybrid breakdown, as a result of mito-nuclear incompatibilities in respiratory complexes of the electron transport system. However, it remains unclear whether hybridization increases the production of reactive oxygen species (ROS) by mitochondria. We used high-resolution respirometry and fluorometry on isolated liver mitochondria to examine mitochondrial physiology and ROS emission in naturally occurring hybrids of pumpkinseed (Lepomis gibbosus) and bluegill (L. macrochirus). ROS emission was greater in hybrids than in both parent species when respiration was supported by complex I (but not complex II) substrates, and was associated with increases in lipid peroxidation. However, respiratory capacities for oxidative phosphorylation, phosphorylation efficiency, and O kinetics in hybrids were intermediate between those in parental species. Flux control ratios of capacities for electron transport (measured in uncoupled mitochondria) relative to oxidative phosphorylation suggested that the limiting influence of the phosphorylation system is reduced in hybrids. This likely helped offset impairments in electron transport capacity and complex III activity, but contributed to augmenting ROS production. Therefore, hybridization can increase mitochondrial ROS production, in support of previous suggestions that mitochondrial dysfunction can induce oxidative stress and thus contribute to hybrid breakdown.

Oxidative cost of interspecific hybridization: a case study of twoTriturusspecies and their hybrids

“…Our results suggest that hybrid individuals are faced with increased ROS production. This was also observed in isolated mitochondria of sunfish hybrids when these were compared with the parents (Du et al, 2017). Regulation of the AOS can be considered as an indirect cost of oxidative stress (Costantini, 2014).…”

“…Boosted anti-oxidant defences in the damselfly (Lestes viridis) and blackbirds (Turdus merula) lead to a trade-off in immune function (Eikenaar et al, 2018;Janssens and Stoks, 2018), while in hybrids of marine copepod, reduced fecundity was associated with disrupted oxidative balance (Barreto and Burton, 2013). Du et al (2017) suggested that increases in ROS production and oxidative stress contribute to the relatively poor competitive ability of sperm in sunfish F 1 hybrids in comparison with that of parental species.…”

“…Interspecific hybridization in newts is often followed by mitonuclear mismatch because of differences in nuclear and mitochondrial DNA in parental species (Maletzky et al, 2008;Arntzen et al, 2009;Gvoždík, 2012). Mitonuclear mismatch can directly affect normal mitochondrial function (OXPHOS pathway), leading to increased electron leak and increased ROS levels (Du et al, 2017), and indirectly to upregulation of the AOS in response to increased ROS production. This upregulation is an energetically costly process, but if ROS production overwhelms anti-oxidant defences, this can further disrupt the oxidative balance in the hybrid, resulting in higher levels of oxidative damage in comparison with the parental species.…”

The genomic impact of historical hybridization with massive mitochondrial DNA introgression

“…TMLHE is involved in carnitine biosynthesis, an antioxidant that might protect mitochondria from oxidative stress [ 84 ]. The control of oxidative stress is an important component of many aspects of physiology and reproduction, and its disruption has been reported to occur in situations of hybridization [ 74 , 85 , 86 ]. These genes are thus candidates to have been affected by cytonuclear co-evolution during and after the hybridization events.…”

Measurement of mitochondrial respiration in permeabilized fish gills

“…The maximal activity (V max ) of citrate synthase (CS) and cytochrome c oxidase (COX) is commonly used as a measure of mitochondrial density (Larsen et al, 2012), so would be expected to correlate with measurements of mitochondrial respiration rate per unit mass of tissue. Activity was assayed at 12°C as previously described (Du et al, 2017;Dawson et al, 2018) using a SpectraMaxPlus 384 spectrophotometer (Molecular Devices, Sunnyvale, CA, USA). Samples were homogenized in 20 volumes of ice-cold homogenization buffer [in mmol l −1 : 100 KH 2 PO 4 , 1 EGTA, 1 EDTA and 1 phenylmethylsulfonyl fluoride (PMSF); pH 7.3].…”