Senescent sperm performance in old male birds

Area of Science:

• Evolutionary biology
• Gerontology
• Reproductive biology

Background:

• Senescence, or the deterioration of traits with age, is poorly understood in birds due to their high metabolic rates.
• Birds are often assumed to exhibit slow senescence, but empirical evidence is limited, especially regarding reproductive functions.

Purpose of the Study:

• To investigate age-related changes in sperm performance in the barn swallow (Hirundo rustica).
• To determine if sperm from older male barn swallows perform differently in female reproductive tract fluid compared to neutral medium.

Main Methods:

• Computer-assisted sperm analysis (CASA) was used to evaluate sperm motility and velocity parameters.
• Sperm from males aged 1-6 years were tested in both a neutral medium and a medium derived from the female reproductive tract.

Main Results:

• Sperm performance significantly declined with age, showing reduced linear movement, track velocity, straight-line velocity, and lower proportions of progressive and motile sperm.
• Sperm from older males exhibited enhanced performance in female medium compared to neutral medium, particularly in track velocity and straight-line velocity.
• Younger males' sperm performed better in neutral medium, while older males' sperm showed a relative improvement in female medium.

Conclusions:

• Sperm performance in barn swallows deteriorates with male age, impacting key reproductive variables.
• Older male barn swallows' sperm show a differential response to female reproductive tract fluid, suggesting an adaptive mechanism potentially related to reproductive strategies.