REINFORCEMENT: A NEW PERSPECTIVE ON AN OLD CONTROVERSY

Area of Science:

• Evolutionary biology
• Speciation research
• Reproductive isolation mechanisms

Background:

• The reinforcement model explains how natural selection can strengthen reproductive isolation between diverging populations.
• Theoretical predictions suggest reinforcement is most effective when postzygotic reproductive isolation is nearly complete.
• Previous selection experiments have often overlooked the role of incomplete postzygotic reproductive isolation.

Purpose of the Study:

• To investigate the role of varying levels of postzygotic reproductive isolation in the process of reinforcement.
• To test whether reinforcement can occur when postzygotic reproductive isolation is incomplete.
• To determine the minimum level of postzygotic reproductive isolation required for reinforcement.

Main Methods:

• Experimental evolution using four treatments of postzygotic reproductive isolation: complete, strong, moderate, and none.
• Selection experiments were conducted over 25 generations.
• Quantification of heterotypic mating frequencies as a measure of reinforcement.

Main Results:

• A significant reduction in heterotypic matings was observed only in the treatment with complete postzygotic reproductive isolation.
• No evidence of reinforcement (decrease in heterotypic matings) was detected in treatments with strong, moderate, or no postzygotic reproductive isolation.
• Incomplete postzygotic reproductive isolation did not facilitate reinforcement.

Conclusions:

• Complete postzygotic reproductive isolation is necessary for reinforcement to occur under the tested experimental conditions.
• Incomplete postzygotic reproductive isolation is insufficient to drive reinforcement, contrary to some interpretations of field observations.
• The findings underscore the importance of considering the degree of reproductive isolation in evolutionary reinforcement studies.