Abstract
ABSTRACTSperm performance is often tightly linked to male reproductive success. In many demersal gobiid fishes, the male attaches sperm embedded in a mucus produced by sperm-duct glands to the nest substrate before spawning takes place. Sperm are activated as the mucus and embedded gland content dissolve into the water. To test the importance of gland content on sperm function in Pomatoschistus minutus, a marine fish with external fertilization, we used a paired experimental design, with spermatozoa tested with and without sperm-duct gland content mixed into seawater. We measured sperm velocity, percentage of motile sperm and sperm viability over time. Sperm were found to swim 7.3% faster when gland content was mixed in the seawater. Percentage motile sperm was unaffected by the gland content. Sperm viability in seawater exceeded 24 h, but was unaffected by the gland content. An increase in sperm velocity of similar magnitude as found here has been shown by others to increase fertilization success. Since velocity-boosting properties of sperm-duct gland content have now been found in three distantly related goby species, this trait appears to be conserved across the Gobiidae family and may aid in reproduction across a range of species and environments.This article has an associated First Person interview with the first author of the paper.
Highlights
Sperm are often viewed as short-lived DNA vectors, with an inverse relationship between their velocity and viability (Ball and Parker, 1996; Møller, 1998; Levitan, 2000; but see Snook, 2005)
To control for a potential effect of sperm numbers on velocity, a general linear model analysis of covariance was performed with velocity of the curvilinear path (VCL) as dependent variable, treatment as factor and percent motile sperm as covariate
We found that the treatment with content from the sperm-duct glands significantly increased the velocity of sperm in the sand goby [tested with SDG content mean±s.e.m
Summary
Sperm are often viewed as short-lived DNA vectors, with an inverse relationship (i.e. a trade-off) between their velocity and viability (Ball and Parker, 1996; Møller, 1998; Levitan, 2000; but see Snook, 2005). This trade-off is expected to arise because both velocity and viability require energy (Levitan, 2000) When this is the case, any increase in one trait would come at the expense of the other, and it is the optimal combination of the two traits that is under selection (Ball and Parker, 1996). The non-gametic content of ejaculate is increasingly being. Despite a growing awareness of the importance of ejaculate content other than sperm, we still know relatively little about the effect of such substances during reproduction, especially among animals with external fertilization
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