Cryptic female choice enhances fertilization success and embryo survival in chinook salmon

Abstract

In this study, we investigated two potentially important intersexual postcopulatory gametic interactions in a population of chinook salmon (Oncorhynchus tshawytscha): (i) the effect of female ovarian fluid (OF) on the behaviour of spermatozoa during fertilization and (ii) the effects of multilocus heterozygosity (MLH) (as an index of male quality) and female-male genetic relatedness on sperm behaviour and male fertilization success when there is sperm competition in the presence of that OF. To do this, we conducted a series of in vitro competitive fertilization experiments and found that, when ejaculates from two males are competing for access to a single female's unfertilized eggs, fertilization success was significantly biased towards the male whose sperm swam fastest in the female's OF. Embryo survival-a measure of fitness-was also positively correlated with both sperm swimming speed in OF and male MLH, providing novel evidence that cryptic female choice is adaptive for the female, enhancing the early survival of her offspring and potentially influencing her fitness.

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

“…Fertilization success (%) is the proportion of 48 genotyped offspring sired by each male in a paired-male fertilization trial. in Chinook salmon (Rosengrave et al, 2016). Our data confirm the suggestion that the impact of ovarian fluid on sperm velocity is indeed a mechanism of CFC to effectively bias male fertilization outcome in Chinook salmon (Rosengrave et al, 2008).…”

“…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). Evidence for a second mechanism of CFC in external fertilizers via gamete interactions derives from studies of marine invertebrates, including tunicates (Scofield et al, 1982), sea urchins (Palumbi, 1999), abalone (Swanson et al, 2001), where proteins on the gamete surfaces facilitate non-random sperm-egg fusions.…”

Postmating Female Control: 20 Years of Cryptic Female Choice

“…For example, heterozygosity can be increased when CFC favors male genotypes that are less similar to the female. Broadly consistent with this idea, a recent study in Chinook salmon Oncorhynchus tshawytscha found that the sperm–OF interaction predicted embryo survival better than did sperm competitive ability alone, providing evidence of the adaptive role of CFC [43]. In mussels, CFC promotes early embryonic viability in a way that is consistent with egg selection for genetically compatible sperm [41].…”

Status Specific Tailoring of Sperm Behavior in an External Fertilizer

“…However, disentangling the separate effects of varying quality of sperm and differing ovarian fluids on fertilization success and offspring quality under sperm competition is challenging. Some authors have demonstrated positive effects of ovarian fluid on sperm velocity (Gasparini and Pilastro, 2011;Evans et al, 2012;Oliver and Evans, 2014;Alonzo et al, 2016;Rosengrave et al, 2016), while Lumley et al (2016) revealed no effect of ovarian fluid on relative offspring fitness. Moreover, the only published intraspecific study exchanging ovarian fluid between eggs from different females documented no overall effect of ovarian fluid on paternity success under sperm competition and no evidence for male-female interactions (Evans et al, 2013).…”