Bioenergetic consequences of sex-specific mitochondrial DNA evolution

Area of Science:

• Mitochondrial genetics
• Evolutionary biology
• Bivalve reproductive biology

Background:

• Mitochondria are typically maternally inherited in animals.
• Doubly uniparental inheritance (DUI) is an exception where mitochondria are inherited from both parents.
• DUI allows for separate evolution of mitochondrial genomes in males and females.

Purpose of the Study:

• To investigate the impact of sex-specific mitochondrial evolution on gamete bioenergetics in bivalves.
• To compare enzyme activity in gametes of Doubly Uniparental Inheritance (DUI) and Strict Maternal Inheritance (SMI) species.
• To understand the bioenergetic strategies associated with different mitochondrial inheritance patterns.

Main Methods:

• Comparative analysis of key metabolic enzymes.
• Enzyme assays for glycolysis, fermentation, fatty acid metabolism, tricarboxylic acid cycle, oxidative phosphorylation, and antioxidant metabolism.
• Focus on gametes from DUI and SMI bivalve species.

Main Results:

• Reorganized bioenergetic pathways were observed in DUI gametes compared to SMI gametes.
• DUI sperm exhibited decreased enzymatic capacity relative to DUI oocytes.
• This reduction was particularly notable at the electron transport system terminus.

Conclusions:

• The observed bioenergetic remodelling in DUI gametes aligns with a reproductive strategy not requiring high energy input for sperm.
• This may facilitate the preservation of the paternally transmitted mitochondrial genome in DUI species.
• The selective pressures (positive or relaxed) driving this sperm phenotype remain uncertain.