Abstracts (first author)
The composition of the sperm membrane across mammals is affected by mass-specifc metabolic rate and the level of sperm competitionPDF
Cellular membranes are key structures affecting cell function. Their characteristics and performance are strongly determined by the fatty-acid composition of the membrane phospholipids. Since higher levels of polyunsaturated fatty acids (PUFAs) are coupled with more metabolically active membranes, the "membrane pacemaker theory of metabolism" proposes that a high content in membrane PUFAs is positively correlated with high mass-specific metabolic rate (MSMR). This theory holds in many somatic cell types investigated so far. 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, they are prone to damage such as lipid peroxidation. We hypothesized that, in order to avoid such damage, and the ensuing impairment of sperm function, sperm cells exhibit a negative relationship between PUFA content and MSMR, since PUFAs are prone to lipid peroxidation, and more lipid peroxidation is likely to occur as metabolism increases. Given that high levels of sperm competition can lead to increased ATP production to fuel higher sperm velocities, we also hypothesized that higher levels of sperm competition would lead to a reduction in the proportion of sperm PUFAs. We performed two comparative studies on mammals (one literature-based, the other being experimental and comparing 4 Mus species that differ in their levels of sperm competition). 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. Our study indicates that the fatty-acid composition of membranes in sperm cells differs from that found in all other cell types, due to unique processes affecting the life of spermatozoa.