Sperm design and variation in the New World blackbirds (Icteridae) |
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Authors: | Stefan Lüpold George M. Linz Tim R. Birkhead |
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Affiliation: | (1) Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK;(2) Kellogg Biological Station, Michigan State University, 3700 Gull Lake Drive, Hickory Corners, MI 49060, USA;(3) USDA/APHIS/WS National Wildlife Research Center, 2110 Miriam Circle, Bismarck, ND 58501, USA |
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Abstract: | 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. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Sperm competition Sperm morphology Sperm velocity Phylogenetic analysis Passerine birds |
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