Morphology-function relationships and repeatability in the sperm of Passer sparrows

Area of Science:

• Evolutionary biology
• Animal reproductive strategies
• Sperm biology

Background:

• Sperm performance is a key factor in male reproductive success, particularly in species with polyandry.
• Understanding sperm traits is crucial for comprehending the evolution of male reproductive strategies.

Purpose of the Study:

• To assess the repeatability of sperm morphology and motility in house sparrows and Spanish sparrows over three breeding seasons.
• To investigate the relationships between sperm morphology and sperm function (motility and longevity).

Main Methods:

• Studied wild-derived captive house sparrows (Passer domesticus) and Spanish sparrows (P. hispaniolensis).
• Measured sperm morphology (total length, component lengths) and motility (swimming speed, longevity) across multiple ejaculates and breeding seasons.

Main Results:

• Total sperm length was highly repeatable, while other morphological components showed moderate repeatability.
• Sperm swimming speed repeatability was lower but significant, suggesting it's a dynamic trait.
• Swimming speed showed unexpected negative correlations with flagellum and total sperm length, and no correlation with midpiece length.
• Total sperm length did not correlate with sperm longevity, contradicting previous findings.

Conclusions:

• Sperm morphology and function relationships in passerine birds are complex and not fully understood.
• Current theoretical predictions regarding sperm morphology and performance may not apply universally across all species.
• Further research is needed to elucidate the intricate links between sperm design and function in avian reproduction.