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During fertilization, an egg and sperm cell fuse to create a new diploid structure. In humans, the process occurs once the egg has been released from the ovary, and travels into the fallopian tubes. The process requires several key steps: 1) sperm present in the genital tract must locate the egg; 2) once there, sperm need to release enzymes to help them burrow through the protective zona pellucida of the egg; and 3) the membranes of a single sperm cell and egg must fuse, with the sperm...

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Related Experiment Video

Updated: Jun 27, 2026

Assessing Differences in Sperm Competitive Ability in Drosophila

Assessing Differences in Sperm Competitive Ability in Drosophila

Published on: August 22, 2013

Sperm competition dynamics: ejaculate fertilising efficiency changes differentially with time.

Tommaso Pizzari¹, Kirsty Worley, Terry Burke

¹Edward Grey Institute, Department of Zoology, University of Oxford, Oxford, UK. tommaso.pizzari@zoo.ox.ac.uk

BMC Evolutionary Biology

|December 18, 2008

Summary

Sperm competition dynamics reveal that ejaculate quality, not just quantity, determines paternity over time. High-quality sperm can outcompete numerous low-quality sperm in domestic hens, Gallus gallus domesticus.

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Area of Science:

Evolutionary Biology
Reproductive Biology
Animal Behavior

Background:

Understanding paternity mechanisms is crucial in evolutionary biology, especially with female promiscuity.
Sperm competition, where ejaculates from multiple males compete for fertilization, is a key factor.
Ejaculate quality, influenced by sperm number and motility, dictates competitive success.

Purpose of the Study:

To investigate how the competitive value of ejaculates changes over time within the female reproductive tract.
To determine the relative importance of sperm number versus sperm quality in sperm competition.

Main Methods:

Experimentally engineered heterospermic ejaculates in domestic hens (Gallus gallus domesticus).
Ejaculates varied in sperm number (large vs. lower) and quality (low vs. high).
Artificial insemination used to introduce mixed ejaculates into females.

Main Results:

Large ejaculates with low-quality sperm fertilized initial eggs.
Smaller ejaculates with high-quality sperm ultimately prevailed in fertilization.
This indicates a temporal shift in paternity determination.

Conclusions:

The competitive value of ejaculates changes significantly over time within the female tract.
This leads to a distinct temporal pattern in paternity outcomes.
Future research should assess the generalizability of these findings across different populations.