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Assessing Differences in Sperm Competitive Ability in Drosophila
Published on: August 22, 2013
Tactic-dependent plasticity in ejaculate traits in the swordtail Xiphophorus nigrensis
1Section of Integrative Biology, University of Texas at Austin, 1 University Station C0930, Austin, TX 78712, USA. chadsmith@mail.utexas.edu
Biology Letters
|April 22, 2011
Summary
Sneaking males in swordtails adjust ejaculate quality based on competitor size, with only smaller males showing plasticity in sperm speed. Sperm number and viability remained unchanged, indicating role-dependent sperm quality.
Area of Science:
- Evolutionary biology
- Animal behavior
- Reproductive strategies
Background:
- Alternative reproductive tactics (ART) are common in nature.
- Males employing sneaking tactics often produce larger ejaculates than defending males.
- Ejaculate traits can be plastic, influenced by social environment and sperm competition.
Purpose of the Study:
- To investigate the effect of competitor tactic on ejaculate traits in the swordtail fish (Xipophorus nigrensis).
- To determine if sperm number, viability, and motility are plastic in response to perceived competition.
- To assess if plasticity in ejaculate traits differs between small (sneaking) and large (courting) males.
Main Methods:
- Males of X. nigrensis were exposed to competitors of different sizes and tactics.
- Sperm number, viability, and swimming speed were measured.
- Comparisons were made between small and large males under different social conditions.
Main Results:
- Sperm swimming speed was significantly higher when males perceived a smaller competitor.
- This plasticity in sperm swimming speed was only observed in small (sneaking) males.
- Sperm number and viability did not differ significantly between social environments for either male tactic.
Conclusions:
- Sperm quality is context-dependent and influenced by the male's reproductive role and perceived competition.
- Plastic responses to the social environment in ejaculate traits can vary between alternative male reproductive tactics.
- This study highlights the complex interplay between male strategy, social environment, and ejaculate evolution.
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