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      Sperm competition and the evolution of sperm design in mammals

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      1 , 2 , 1 , , 1 ,

      BMC Evolutionary Biology

      BioMed Central

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          Abstract

          Background

          The influence of sperm competition upon sperm size has been a controversial issue during the last 20 years which remains unresolved for mammals. The hypothesis that, when ejaculates compete with rival males, an increase in sperm size would make sperm more competitive because it would increase sperm swimming speed, has generated contradictory results from both theoretical and empirical studies. In addition, the debate has extended to which sperm components should increase in size: the midpiece to accommodate more mitochondria and produce more energy to fuel motility, or the principal piece to generate greater propulsion forces.

          Results

          In this study we examined the influence of sperm competition upon sperm design in mammals using a much larger data set (226 species) than in previous analyses, and we corrected for phylogenetic effects by using a more complete and resolved phylogeny, and more robust phylogenetic control methods. Our results show that, as sperm competition increases, all sperm components increase in an integrated manner and sperm heads become more elongated. The increase in sperm length was found to be associated with enhanced swimming velocity, an adaptive trait under sperm competition.

          Conclusions

          We conclude that sperm competition has played an important role in the evolution of sperm design in mammals, and discuss why previous studies have failed to detect it.

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          Most cited references55

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          SPERM COMPETITION AND ITS EVOLUTIONARY CONSEQUENCES IN THE INSECTS

          Biological Reviews, 45(4), 525-567
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            Ejaculate Cost and Male Choice

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              Sperm in competition: not playing by the numbers.

              The outcome of sperm competition is mediated largely by the relative numbers of sperm from competing males. However, substantial variation in features of sperm morphology and behaviour, such as length, longevity and motility, exists and researchers have suggested that this variation functions in postcopulatory sexual selection. Recent studies have determined the effect of these sperm-quality traits on fertilization success and a synthesis of this literature reveals that they are important in both sperm competition and cryptic female choice. To understand how postcopulatory sexual selection influences sperm traits, future research should determine sex-specific interactions that influence paternity, identify genetic correlations between ejaculate characters, quantify the relative costs of producing different sperm traits, and test assumptions of models of sperm quality evolution. Such research will shed light on what evolutionary pressures are responsible for the diversity in sperm morphometry and behaviour.
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                Author and article information

                Journal
                BMC Evol Biol
                BMC Evolutionary Biology
                BioMed Central
                1471-2148
                2011
                13 January 2011
                : 11
                : 12
                Affiliations
                [1 ]Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), José Gutiérrez Abascal 2, 28006 Madrid, Spain
                [2 ]Laboratorio de Biología del Comportamiento, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Vélez Sarsfield 299, X5000JJC Córdoba, Argentina
                Article
                1471-2148-11-12
                10.1186/1471-2148-11-12
                3030547
                21232104
                9b1597c9-5633-44b7-9552-5a790768e5e9
                Copyright ©2011 Tourmente et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Research Article

                Evolutionary Biology

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