Modelling the proximate basis of salmonid life-history variation, with application to Atlantic salmon, Salmo salar L.

Alternative life histories shape brain gene expression profiles in males of the same population

“…Surprisingly, the cluster analysis showed that brain gene expression profiles of sneaker males were more similar to those of immature females than immature males. Although evidence at the molecular and cellular level is limited, this suggests that early maturation as a sneaker could be the default developmental pathway in salmon, with males that fail to reach the threshold size to develop into sneakers, the immature males of this study, being the ones adopting an alternative tactic by actively repressing maturation (Thorpe et al 1998). Indeed, a high percentage of the genes that were upregulated in sneaker males compared with immature males were not significantly different when compared with female brains.…”

Why Do Some Fish Fight More than Others?

“…It often happens that individual animals adopt a lifehistory pattern that involves growing fast and maturing at an early age, as opposed to growing more slowly and maturing later (Thorpe et al 1998). The balance of fitness costs and benefits of early versus late maturation explain why the two life-history patterns coexist over evolutionary time.…”

Ejaculate Allocation and Sperm Competition in Alternative Reproductive Tactics of Salmon and Trout: Implications for Aquaculture

“…This life history strategy is also associated with the impaired sea-water adaptability and reduced smoltification (Myers 1984, Lundqvist et al 1989. Male success is more dependent on social environment than is female success, which is dependent on the allometric relation between body size and gonad mass; therefore no single optimal life history is expected (Thorpe et al 1998). Several decisions about the number of winters in the sea before returning to spawning may be exhibited within a single cohort.…”

“…Several decisions about the number of winters in the sea before returning to spawning may be exhibited within a single cohort. This results in the variable proportions of precociously mature parr, "grilse" and anadromous males that have spent a varying number of years in sea (Thorpe et al 1998). In reproductive biology, male quality equals individual reproductive success.…”

“…Reaction norms are genotype responses describing the manner individuals respond to environmental change within a population (Woltereck 1909). In salmonid fishes, growth rates influence choice of male mating tactic; males in good condition tend to mature early whereas males in poor condition tend to postpone reproduction in favour of prolonged body growth (Hutchings & Myers 1994;Thorpe et al 1998). This choice is a "threshold trait", where a liability toward maturation-age decision depends on the phenotype's position relative to some physiological (or environmental, see below) threshold value.…”