Mating success of alternative male phenotypes and evidence for frequency-dependent selection in Chinook salmon, Oncorhynchus tshawytscha

Abstract

As with other species, frequency-dependent selection during reproduction has long been proposed as an important mechanism in maintaining alternative male reproductive phenotypes in Pacific salmon ( Oncorhynchus spp.). Jack salmon mature one year earlier than the youngest females in a population and are much smaller than older “adult” males. We tested the hypothesis that mating success of both phenotypes is consistent with the frequency-dependent selection model. By holding male density constant and varying the frequency of adults and jacks in eight separate breeding groups, we found that adult male access to females, participation in spawning events, and adult-to-fry reproductive success increased with their decreasing frequency in a breeding group. Jacks exhibited the same pattern (increasing success with decreasing frequency), although the relationships were not as strong as for adults. Overall, jack and adult males mated with a similar number of females, but jacks sired only 20% of all offspring. Observational data suggested that adult males benefited from sperm precedence associated with their ability to court females and enter the nest first at the time of spawning. Our work provides the first experimental evidence of frequency-dependent selection during mating in the family Salmonidae.

Breeding success of four male life history types of spring Chinook Salmon spawning in an artificial stream

“…The aggressive behavior of large anadromous males, for instance, often delayed sperm release by competitors. This gave their sperm precedence over a Relative breeding success was estimated by dividing the mean number of offspring produced in a test group by either jacks, yearling, or sub yearling precocious males by the mean number of offspring produced by large anadromous males any released by rivals and therefore increased the likelihood they would fertilize most of the eggs in a multiple-male spawning (Berejikian et al 2010). Large salmonid males also release significantly greater volumes of milt (Taborsky 1998) at higher pressures (Mjolnerod et al 1998) than smaller competitors.…”

“…Additionally, the operational sex ratio or number of males competing for each female, influences intra-sexual competition and the expression of behavioral tactics within and across male life history types (Emlen and Oring 1977;Quinn et al 1996). Finally, the prevalence of males representing different life history types may also determine how many offspring each type produces and the behavioral tactics that are employed on spawning grounds (Berejikian et al 2010).…”

Co-localization of growth QTL with differentially expressed candidate genes in rainbow trout

“…Changes in gene expression related to the early maturation of male salmonids (Berejikian et al 2010;Guiry et al 2010) could also account for the detection of different QTL and the co-localization of candidate genes with those QTL in mixed-sex and all-female populations. This study examined rainbow trout at 15 months of age before the onset of maturation; however, males may mature precociously at 2 years of age, with significant increases in plasma levels of 11-ketotestosterone (11-KT) seen several months prior to the onset of maturation (Campbell et al 2003).…”

Ovarian fluid impacts flagellar beating and biomechanical metrics of sperm between alternative reproductive tactics

“…Chinook salmon is a semelparous (reproduce once and then die) species, where larger 'hooknose' males mature after 3-5 years on average and display many of the typical guard characters, such as exaggerated secondary sexual characteristics and male-to-male aggressive behaviour (Berejikian et al, 2010;Butts et al, 2012b). In contrast, parasitic jack males reach sexual maturity precociously, after 2 years, and try to outcompete hooknose males during the spawning season by investing disproportionately in reproductive traits, e.g.…”

“…In contrast, parasitic jack males reach sexual maturity precociously, after 2 years, and try to outcompete hooknose males during the spawning season by investing disproportionately in reproductive traits, e.g. gonads and sperm swimming performance (Berejikian et al, 2010;Flannery et al, 2013;Young et al, 2013).…”