A potential role for restricted intertactical heritability in preventing intralocus conflict

Intralocus sexual conflict, which arises when the same trait has different fitness optima in males and females, reduces population growth rates. Recently, evolutionary biologists have recognized that intralocus conflict can occur between morphs or reproductive tactics within a sex and that intralocus tactical conflict might constrain tactical dimorphism and population growth rates just as intralocus sexual conflict constrains sexual dimorphism and population growth rates. However, research has only recently focused on sexual and tactical intralocus conflict simultaneously, and there is no formal theory connecting the two. We present a graphical model of how tactical and sexual conflict over the same trait could constrain both sexual and tactical dimorphisms. We then use Coho salmon (Oncorhynchus kisutch), an important species currently protected under the Endangered Species Act, to investigate the possibility of simultaneous sexual and tactical conflict. Larger Coho males gain access to females through fighting while smaller males are favored through sneaking tactics, and female reproductive success is positively correlated with length. We tested for antagonistic selection on length at maturity among sexes and tactics and then used parent–offspring regression to calculate sex- and tactic-specific heritabilities to determine whether and where intralocus conflict exists. Selection on length varied in intensity and form among tactics and years. Length was heritable between dams and daughters (h2 ± 95% CI = 0.361 ± 0.252) and between fighter males and their fighter sons (0.867 ± 0.312), but no other heritabilities differed significantly from zero. The lack of intertactical heritabilities in this system, combined with similar selection on length among tactics, suggests the absence of intralocus conflict between sexes and among tactics, allowing for the evolution of sexual and tactical dimorphisms. Our results suggest that Coho salmon populations are unlikely to be constrained by intralocus conflict or artificial selection on male tactic

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

Identifying Critical Periods of Growth and Mortality in Pacific Salmon and Deciphering Underlying Mechanisms

Size-selective mortality (SSM) is a significant force regulating recruitment of salmon. The life stage(s) and habitat(s) in which SSM occurs can vary among species, stocks, and life history strategies. Moreover, the relationship between juvenile growth and survival is unclear for most salmon stocks. The first marine growth season is commonly regarded as a critical period for growth and survival. For ESA-listed Puget Sound Chinook salmon, preliminary studies suggest that: at least one critical period occurs during the first marine growth season; growth is limited more by food supply than energetic quality of prey or thermal regime; and higher growth and survival rates correspond with higher contributions of key prey like crab larvae. We can identify critical periods using scales to create growth histories of a juvenile cohort sampled serially at successive life stages throughout its first marine growth season. Divergences in growth trajectories indicate reduced contributions of smaller members to subsequent life stages. These divergences indicate critical periods of growth and survival and the magnitude of SSM. We can diagnose factors affecting growth during critical periods through bioenergetics modeling simulations linked to directed sampling of diet, growth and environmental conditions. This approach could improve run forecasting and focus restoration efforts