Pronounced within-individual plasticity in sperm morphometry across social environments

Area of Science:

• Reproductive Biology
• Behavioral Ecology
• Evolutionary Biology

Background:

• Sperm morphometry is crucial for male reproductive success and typically considered under stabilizing selection.
• Recent evidence suggests sperm morphometry may be a phenotypically plastic trait, adaptable to environmental conditions.
• Behavioral strategies, particularly aggression, might influence sperm characteristics.

Purpose of the Study:

• To investigate if behavioral strategies (aggression) in color polymorphic Gouldian finches influence sperm morphometry.
• To determine if social environment affects sperm size and shape in male finches.
• To explore the role of hormonal changes in mediating sperm morphometry adjustments.

Main Methods:

• Comparative analysis of sperm morphometry in aggressive (red) and nonaggressive (black) male Gouldian finches.
• Manipulation of social environments to create varying competitive pressures.
• Measurement of sperm traits, stress hormones, and sex steroid hormones.

Main Results:

• Male Gouldian finches exhibit significant within-individual phenotypic plasticity in sperm morphometry across different social environments.
• Males in high-competition environments increased sperm midpiece length, while those in lower competition increased flagellum length.
• Hormonal changes influenced sperm traits in red males but not black males, indicating non-hormonal factors are also involved.

Conclusions:

• Male Gouldian finches can adjust their sperm morphometry in response to social and competitive environments.
• Phenotypic plasticity in sperm traits allows males to adapt reproductive characteristics to varying conditions.
• Behavioral strategies and social context play a role in modulating sperm morphometry, independent of hormonal levels alone.