Sex‐specific heritabilities for length at maturity among Pacific salmonids and their consequences for evolution in response to artificial selection

Abstract

Artificial selection, whether intentional or coincidental, is a common result of conservation policies and natural resource management. To reduce unintended consequences of artificial selection, conservation practitioners must understand both artificial selection gradients on traits of interest and how those traits are correlated with others that may affect population growth and resilience. We investigate how artificial selection on male body size in Pacific salmon (Oncorhynchus spp.) may influence the evolution of female body size and female fitness. While salmon hatchery managers often assume that selection for large males will also produce large females, this may not be the case—in fact, because the fastest‐growing males mature earliest and at the smallest size, and because female age at maturity varies little, small males may produce larger females if the genetic architecture of growth rate is the same in both sexes. We explored this possibility by estimating sex‐specific heritability values of and natural and artificial selection gradients on length at maturity in four populations representing three species of Pacific salmon. We then used the multivariate breeder's equation to project how artificial selection against small males may affect the evolution of female length and fecundity. Our results indicate that the heritability of length at maturity is greater within than between the sexes and that sire–daughter heritability values are especially small. Salmon hatchery policies should consider these sex‐specific quantitative genetic parameters to avoid potential unintended consequences of artificial selection.

Utility of parentage‐based tagging for monitoring Coho salmon (Oncorhynchus kisutch) in the interior Columbia River basin

“…In natural populations of Coho salmon, it has been estimated that jack males can contribute 35% of the spawning effort, whereas in a hatchery population jacks contributed only 2% (Van Doornik et al., 2002). In addition, not including jacks in hatchery broodstocks can actually limit the adult female size over time due to negative intersexual heredity (i.e., differences in the patterns of heredity among sexes) from selection against jacks, thereby limiting female reproductive output (Gamble & Calsbeek, 2023). Purposefully allowing more jacks into a hatchery broodstock would increase gene flow among broodlines and would be expected to improve the long‐term diversity and sustainability of reintroduced Coho salmon.…”

“…In addition, not including jacks in hatchery broodstocks can actually limit the adult female size over time due to negative intersexual heredity (i.e., differences in the patterns of heredity among sexes) from selection against jacks, thereby limiting female reproductive output (Gamble & Calsbeek, 2023) to 2020, an average of only 11% were jacks (median value of 6%).…”

Selection among critically endangered landlocked salmon (Salmo salar m. sebago) families in survival and growth traits across early life stages and in different environments

“…Maximizing genetic diversity originally preserved in hatchery strains should be prioritized in supportive breeding programs aiming to promote the conservation and productivity of wild salmonid stocks (Withler et al, 2014). Nevertheless, the avoidance of artificial selection and consequent genetic changes remain an obvious challenge (Gamble & Calsbeek, 2023;Neff et al, 2011;Pasquet, 2019;Ryman & Laikre, 1991). In practical broodstock management, families of salmon are often combined already before hatching (at the F I G U R E 3 Sire and dam estimates (on logit scale) for the likelihood of onesummer-old salmon to become sampled after the first summer in hatchery and seminatural rearing environments.…”