Alternative life histories in the Atlantic salmon: genetic covariances within the sneaker sexual tactic in males

Abstract

Alternative reproductive tactics are ubiquitous in many species. Tactic expression often depends on whether an individual's condition surpasses thresholds that are responsible for activating particular developmental pathways. Two central goals in understanding the evolution of reproductive tactics are quantifying the extent to which thresholds are explained by additive genetic effects, and describing their covariation with condition-related traits. We monitored the development of early sexual maturation that leads to the sneaker reproductive tactic in Atlantic salmon (Salmo salar L.). We found evidence for additive genetic variance in the timing of sexual maturity (which is a measure of the surpassing of threshold values) and body-size traits. This suggests that selection can affect the patterns of sexual development by changing the timing of this event and/or body size. Significant levels of covariation between these traits also occurred, implying a potential for correlated responses to selection. Closer examination of genetic covariances suggests that the detected genetic variation is distributed along at least five directions of phenotypic variation. Our results show that the potential for evolution of the life-history traits constituting this reproductive phenotype is greatly influenced by their patterns of genetic covariance.

Genetic variation underlying the expression of a polyphenism

“…Although there are cases of alternative reproductive strategies where the phenotype adopted by a male is determined entirely by the alleles at a single locus (Shuster, 2008), several cases reflect the conditional expression of male phenotypes in response to environmental cues (Emlen, 2008). Despite conditional male dimorphisms being common, surprisingly few empirical studies have explored the importance of genetic variation in this type of plasticity (but see Emlen, 1996;Doums et al, 1998;Tomkins & Brown, 2004;Unrug et al, 2004;Pá ez et al, 2011). As far as we know, the present study is the first to report the effects of establishing inbred lines to directly investigate the genetic variation for the switchpoint that underlies the expression of male polyphenism.…”

“…More recently, Páez et al. (2011) used a pedigree design with both maternal and paternal half‐sib structure and unveiled additive genetic variance in the switchpoint that determines the timing of sexual maturity (and consequently male polyphenism) in the Atlantic salmon.…”

Reduced fitness of Atlantic salmon released in the wild after one generation of captive breeding

“…), and a genetic correlation was uncovered between sexual maturation and anadromous migration in Atlantic salmon (Paez et al. ). Consequently, a lower survival of smolt‐stocked fish may favor a SSW strategy at the cost of a lower fecundity.…”

Enhanced growth reduces precocial male maturation in Atlantic salmon

“…An intriguing feature of this life‐history dichotomy involves the proximate and ultimate mechanisms with which stream‐dwelling male parr follow a developmental trajectory towards precocial maturation or anadromy. Current evidence suggests that precocious maturation is initiated by parr reaching a polygenic performance threshold that, within populations, correlates with fast growth/size at age (Hutchings & Myers 1994; Aubin‐Horth & Dodson 2004; Piché, Hutchings & Blanchard 2008; Páez, Bernatchez & Dodson 2011). Proximate causation is thought to be associated with the available energy (lipid) reserves, and the rate of energy reserve allocation, an individual has attained prior to the onset of environmental triggers initiating sexual development (Thorpe et al.…”