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. 2011 Jan 13:11:12.
doi: 10.1186/1471-2148-11-12.

Sperm competition and the evolution of sperm design in mammals

Maximiliano Tourmente  1 , Montserrat Gomendio, Eduardo R S Roldan
Affiliations

Sperm competition and the evolution of sperm design in mammals

Maximiliano Tourmente et al. BMC Evol Biol. .

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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Figures

Figure 1
Figure 1
Relation between sperm competition and sperm dimensions in eutherian mammals. Relations between relative testes mass and (A) total sperm length (μm), (B) sperm head length (μm), (C) sperm midpiece length (μm), (D) sperm principal piece length (μm), (E) total sperm flagellum length (μm), and (F) sperm head length/width ratio, among eutherian mammals.
Figure 2
Figure 2
Relations between sperm velocity, sperm size and sperm competition in eutherian mammals. Relations between (A) sperm straight-line swimming velocity (μm/s) and total sperm length (μm), and (B) sperm straight line swimming velocity and relative testes mass, in 26 species of eutherian mammals.
Figure 3
Figure 3
Relation between sperm velocity and sperm head/flagellum ratio in eutherian mammals. Relations were examined between sperm straight-line swimming velocity (μm/s) and the proportion between sperm head length (μm) and sperm total flagellum length (μm), in 19 species of eutherian mammals.
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