Resolving variation in the reproductive tradeoff between sperm size and number
| Autor: | Geoff A. Parker, Stefan Lüpold, Kate L. Durrant, Tim R. Birkhead, Simone Immler, Scott Pitnick, Sara Calhim |
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| Přispěvatelé: | University of Zurich, Immler, Simone |
| Rok vydání: | 2011 |
| Předmět: |
Male
0106 biological sciences endocrine system media_common.quotation_subject Zoology 010603 evolutionary biology 01 natural sciences Competition (biology) Sperm displacement 10127 Institute of Evolutionary Biology and Environmental Studies 03 medical and health sciences Human fertilization biology.animal Testis Animals Passeriformes Sperm competition reproductive and urinary physiology 030304 developmental biology media_common 1000 Multidisciplinary 0303 health sciences Multidisciplinary Sperm Count biology urogenital system Ecology Reproduction fungi Biological Sciences Models Theoretical Spermatozoa Sperm Passerine Sexual selection 570 Life sciences 590 Animals (Zoology) Drosophila Female |
| Zdroj: | Proceedings of the National Academy of Sciences of the United States of America |
| ISSN: | 1091-6490 0027-8424 |
| DOI: | 10.1073/pnas.1009059108 |
| Popis: | Spermatozoa are amongst the most variable cells, and three factors are thought to account for this variation in design: fertilization mode, phylogeny, and postcopulatory sexual selection. In addition, it has long been assumed that a tradeoff exists between sperm size and number, and although postcopulatory sexual selection affects both traits, empirical evidence for a tradeoff has so far been elusive. Our recent theoretical model predicts that the nature of a direct tradeoff between sperm size and number varies with sperm competition mechanism and sperm competition risk. We test these predictions using a comparative approach in two very different taxa with different sperm competition mechanisms: passerine birds (mechanism: simple raffle) and Drosophila fruit flies (sperm displacement). We show that in both groups, males increase their total ejaculate investment with increasing sperm competition risk, but whereas passerine birds allocate disproportionately to sperm number, drosophilids allocate disproportionately to sperm size. This striking difference between the two groups can be at least partly explained by sperm competition mechanisms depending on sperm size relative to the size of the female reproductive tract: in large animals (passerines), sperm numbers are advantageous in sperm competition owing to dilution inside the female tract, whereas in small animals (drosophilids), large sperm are advantageous for physical competition (sperm displacement). Our study provides two important results. First, we provide convincing evidence for the existence of a sperm size–number tradeoff. Second, we show that by considering both sperm competition mechanism and dilution, can we account for variation in sperm size between different taxa. |
| Databáze: | OpenAIRE |
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