Long sperm fertilize more eggs in a bird

Area of Science:

• Evolutionary biology
• Reproductive biology
• Animal behavior

Background:

• Sperm competition exerts strong selective pressures on sperm traits.
• Sperm size and swimming velocity are known to influence fertilization success.
• The interplay between sperm length, velocity, and fertilization success remains understudied.

Purpose of the Study:

• To investigate the impact of sperm total length on fertilization success in the zebra finch (Taeniopygia guttata).
• To determine the role of sperm length in the context of sperm competition, considering its influence on sperm swimming velocity.

Main Methods:

• Conducted sperm competition experiments using pairs of male zebra finches with manipulated sperm length and swimming speed.
• Assessed the number of sperm reaching the ova and the fertilization success rate.

Main Results:

• Males producing longer sperm achieved greater success in sperm competition.
• Longer sperm increased both the number of sperm reaching the ova and the fertilization rate.
• Sperm length emerged as the primary determinant of sperm competition outcomes.

Conclusions:

• Sperm length is a critical factor driving the outcome of sperm competition in zebra finches.
• Complex interactions between male and female reproductive traits may also influence fertilization success.
• Potential mechanisms include differential sperm storage and utilization by females.