Abstract
The sperm membrane is a key structure affecting sperm function and thus reproductive success. Spermatozoa are highly specialized and differentiated cells that undergo a long series of processes in the male and female reproductive tracts until they reach the site of fertilization. During this transit, the sperm membrane is prone to damage such as lipid peroxidation. The characteristics and performance of the sperm membrane are strongly determined by the fatty-acid composition of membrane phospholipids. Polyunsaturated fatty-acids (PUFAs) are the most prone to lipid peroxidation. Lipid peroxidation and other types of oxidative damage increase with higher metabolism and with higher levels of sperm competition due to the increased ATP production to fuel higher sperm velocities. Consequently, we hypothesized that, in order to avoid oxidative damage, and the ensuing impairment of sperm function, sperm cells exhibit a negative relationship between PUFA content and mass-specific metabolic rate (MSMR). We also hypothesized that higher sperm competition leads to a reduction in the proportion of sperm PUFAs. We performed a comparative study in mammals and found that high MSMR and high levels of sperm competition both promote a decrease in the proportion of PUFAs that are more prone to lipid peroxidation. The negative relationship between MSMR and these PUFAs in sperm cells is surprising, because a positive relationship is found in all other cell types so far investigated. Our results support the idea that the effects of MSMR and sperm competition on sperm function can operate at very different levels.
Highlights
The efficient functionality of spermatozoa determines the reproductive success of males (Yanagimachi, 1994)
We performed a comparative study in mammals and found that high mass-specific metabolic rate (MSMR) and high levels of sperm competition both promote a decrease in the proportion of Polyunsaturated fatty25 acids (PUFAs) that are more prone to lipid peroxidation
We found that high MSMR and high levels of sperm competition both promote a decrease in the proportion of PUFAs that are more prone to lipid peroxidation
Summary
The efficient functionality of spermatozoa determines the reproductive success of males (Yanagimachi, 1994). Sperm function differs greatly among species and it is specially affected by mass-specific metabolic rate (MSMR) (Lüpold, 2013) and sperm competition (Gómez Montoto et al, 2011; Lüpold, 2013); sperm competition occurs when females mate with more than one male and the sperm of those males compete to fertilize the female’s ova (Parker, 1970; Birkhead & Møller, 1998). The proportion of different types of fatty acids can influence many aspects of membrane function (Hulbert & Else, 1999). A key difference among these different types of fatty acids is their level of unsaturation, which is determined by the number of double bonds within the molecule (Wathes et al, 2007). The most polyunsaturated PUFA is docosahexaenoic acid (DHA), with six double bonds
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