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Sperm Design and Variation in the New World Blackbirds (Icteridae)
USDA National Wildlife Research Center - Staff Publications
  • Stefan Lüpold, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
  • George M. Linz, USDA/APHIS/WS National Wildlife Research Center
  • Tim R. Birkhead, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
Date of this Version
Published in Behav Ecol Sociobiol (2009) 63:899–909.

Post-copulatory sexual selection (PCSS) is thought to be one of the evolutionary forces responsible for the rapid and divergent evolution of sperm design. However, whereas in some taxa particular sperm traits are positively associated with PCSS, in other taxa, these relationships are negative, and the causes of these different patterns across taxa are poorly understood. In a comparative study using New World blackbirds (Icteridae), we tested whether sperm design was influenced by the level of PCSS and found significant positive associations with the level of PCSS for all sperm components but head length. Additionally, whereas the absolute length of sperm components increased, their variation declined with the intensity of PCSS, indicating stabilising selection around an optimal sperm design. Given the diversity of, and strong selection on, sperm design, it seems likely that sperm phenotype may influence sperm velocity within species. However, in contrast to other recent studies of passerine birds, but consistent with several other studies, we found no significant link between sperm design and velocity, using four different species that vary both in sperm design and PCSS. Potential reasons for this discrepancy between studies are discussed.

Citation Information
Stefan Lüpold, George M. Linz and Tim R. Birkhead. "Sperm Design and Variation in the New World Blackbirds (Icteridae)" (2009)
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