Abstract
Sperm competition is a prevalent phenomenon that drives the evolution of sperm function. High levels of sperm competition lead to increased metabolism to fuel higher sperm velocities. This enhanced metabolism can result in oxidative damage (including lipid peroxidation) and damage to the membrane. We hypothesized that in those species experiencing high levels of sperm competition there are changes in the fatty-acid composition of the sperm membrane that makes the membrane more resistant to oxidative damage. Given that polyunsaturated fatty acids (PUFAs) are the most prone to lipid peroxidation, we predicted that higher sperm competition leads to a reduction in the proportion of sperm PUFAs. In contrast, we predicted that levels of sperm competition should not affect the proportion of PUFAs in somatic cells. To test these predictions, we quantified the fatty-acid composition of sperm, testis and liver cells in four mouse species (genus Mus) that differ in their levels of sperm competition. Fatty-acid composition in testis and liver cells was not associated to sperm competition levels. However, in sperm cells, as predicted, an increase in sperm competition levels was associated with an increase in the proportion of saturated fatty-acids (the most resistant to lipid peroxidation) and by a concomitant decrease in the proportion of PUFAs. Two particular fatty acids were most responsible for this pattern (arachidonic acid and palmitic acid). Our findings thus indicate that sperm competition has a pervasive influence in the composition of sperm cells that ultimately may have important effects in sperm function.
Highlights
Sperm competition occurs when the spermatozoa of two or more males compete for the fertilization of the same ovum (Parker, 1970; Birkhead and Møller, 1998)
We found that relative testes size (RTS) in the four species followed the pattern that we reported in previous studies, being lowest in M. pahari, Thomas (0.2460.06; range: 0.13–0.29), followed by M. musculus, Linnaeus (0.3660.05; range: 0.27– 0.40), M. spretus, Lataste (1.1960.11; range: 1.05–1.34) and M. spicilegus, Petenyi (1.4860.06; range: 1.41–1.55; F3,165115.3, p,0.0001)
If species differences in the percentage of a particular group of fatty acids were to follow a pattern similar to the levels of sperm competition inferred from RTS, fatty-acid values should be M. pahari,M. musculus,M. spretus,M. spicilegus if there is a positive relation, or the opposite pattern if the relation is negative
Summary
Sperm competition occurs when the spermatozoa of two or more males compete for the fertilization of the same ovum (Parker, 1970; Birkhead and Møller, 1998). Sperm competition is a prevalent phenomenon and its occurrence leads to several. In rodents, high levels of sperm competition result in a higher proportion of spermatozoa that are morphologically normal, motile, and capable of reaching and fertilizing the ovum (Gomendio et al, 2006; Gomez Montoto et al, 2011b), as well as in modifications in sperm dimensions that may result in improvements in sperm movement (Gomendio and Roldan, 2008; Tourmente et al, 2011). Sperm swimming velocity, an important feature of sperm function, is higher in those species that experience high levels of sperm competition (Fitzpatrick et al, 2009; Kleven et al, 2009; Gomez Montoto et al, 2011a; Tourmente et al, 2011; Lupold, 2013)
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