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09:34
Assessing Differences in Sperm Competitive Ability in Drosophila
Published on: August 22, 2013
Postcopulatory sexual selection is associated with reduced variation in sperm morphology
Sara Calhim1, Simone Immler, Tim R Birkhead
1Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom. s.calhim@sheffield.ac.uk
Plos One
|May 4, 2007
Summary
Postcopulatory sexual selection shapes sperm morphology within species. Intense sexual selection reduces variation in sperm traits, leading to a species-specific optimum. This evolutionary pressure operates at the intraspecific level.
Area of Science:
- Evolutionary biology
- Reproductive biology
- Animal behavior
Background:
- Postcopulatory sexual selection influences male reproductive traits, including sperm morphology.
- Previous research primarily focused on interspecific variation in sperm morphology due to sperm competition.
- This study investigates the role of sexual selection in intraspecific variation of sperm morphology in birds.
Purpose of the Study:
- To test the hypothesis that intraspecific variation in sperm morphology is driven by postcopulatory sexual selection levels.
- To determine if sexual selection acts on sperm morphology within species, not just between species.
Main Methods:
- Examined sperm morphology in passerine birds.
- Used relative testes size as a proxy for sperm competition level.
- Assessed extrapair paternity levels as another proxy for sperm competition.
Main Results:
- Found a negative association between intermale variation in sperm morphology and the degree of postcopulatory sexual selection.
- This relationship was independent of phylogenetic history.
- Evidence suggests sexual selection significantly impacts sperm morphology variation within species.
Conclusions:
- Postcopulatory sexual selection influences sperm morphology evolution at the intraspecific level.
- Intense sexual selection reduces variation, promoting a species-specific optimal sperm phenotype.
- Sexual selection acts as a stabilizing force within species, decreasing variation in sperm morphology.
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