Effects of ovarian fluid on sperm velocity in Arctic charr (Salvelinus alpinus)

Abstract

Numbers of studies in externally fertilizing fish species provide evidence for an effect of ovarian fluid on sperm motility characteristics such as duration of forward mobility, velocity or percent motile sperm cells. Yet, because of variations among females in the quality of their ovarian fluid, such effects might differ between individuals. Additionally, ovarian fluid from different females could also be expected to affect each ejaculate differently, resulting in cryptic female choice. In this study on Artic charr (Salvelnius alpinus), sperm velocity from several males was measured in the diluted ovarian fluid of several females according to a fully balanced crossing design. This design allowed us to estimate variations among females in the effect of their ovarian fluid on the velocity of sperm from different males, and to detect variations among males in the ability of their sperm to swim in ovarian fluid. Sperm velocity was estimated by computer-assisted sperm analysis. Average velocity was found to vary among females, with some females having constantly higher velocity measurements in their ovarian fluid, and among males, indicating that some males had overall faster sperm in ovarian fluid than others. Moreover, variation in sperm velocity was shown to depend on individual female-male interactions. Our results document that females vary in the effect of their ovarian fluid on sperm velocity and that their ovarian fluid may stimulate sperm velocity according to individual characteristics of males. This latter result suggests a potential mechanism for cryptic female choice.

Sexual selection for genetic compatibility: the role of the major histocompatibility complex on cryptic female choice in Chinook salmon (Oncorhynchus tshawytscha)

“…These results are similar to previous studies in Arctic charr (Urbach et al, 2005) and Chinook salmon (Rosengrave et al, 2008). Further, we found that the female-male interaction significantly determined sperm velocity and represented the major variance component, which is in line with previous findings in salmonid fish (Urbach et al, 2005;Rosengrave et al, 2008).…”

“…Similar to related studies (Urbach et al, 2005;Rosengrave et al, 2008) we have detected that sperm velocity can mainly be attributed to sperm-ovarian fluid interaction effects and to a smaller degree to male effects. Thus, in our experiment, female-male interaction effects appear to be the main driver of sperm velocity, which significantly impacts fertilization success, indicating the presence of CFC.…”

“…Prior work in several fish species has shown that ovarian fluid, a viscous substance surrounding the spawned ova, enhances sperm longevity, per cent motility, path linearity and sperm velocity compared to water (for example, Litvak and Trippel, 1998;Turner and Montgomerie, 2002;Rosengrave et al, 2008;Galvano et al, 2013). The degree of stimulation of sperm velocity by the ovarian fluid is greatly explained by male-female interactions, which is indicative of the presence of CFC acting to promote gamete fusions of particular female-male combinations (Urbach et al, 2005;Rosengrave et al, 2008). Because sperm velocity is positively linked with fertilization success in fish (Gage et al, 2004;Boschetto et al, 2011;Evans et al, 2013;Rosengrave et al, 2016), it is possible that the differential stimulation of sperm velocity by ovarian fluid represents a mechanism of CFC (Rosengrave et al, 2008).…”

Female mediation of competitive fertilization success in Drosophila melanogaster

“…Similarly, we found that neither female genetic background nor SR length significantly affected sperm velocity. This negative result is potentially important; although a few previous investigations have shown significant female and/or male-by-female interaction effects on sperm velocity (23)(24)(25)(26), all these studies have been conducted in vitro with externally fertilizing species and were not designed to explore genetic variation.…”

Delineating the roles of males and females in sperm competition

“…Previous work on O. tshawytscha and other salmonid fishes has revealed that ovarian fluid (OF), which forms an extracellular matrix surrounding externally spawned eggs, upregulates sperm motility [20] and differentially mediates the swimming velocities of sperm from conspecific males. Specifically, sperm tested in the presence of OF from certain females perform better (swim faster) than when tested with others, and such patterns can be non-transitive across different male-female pairings [21][22][23][24]. As relative differences in sperm swimming velocity have been shown to be associated with sperm competitiveness in salmonid fishes [25], OF has been implicated as a potential arbiter of cryptic female choice in these taxa [23].…”