A potential role for restricted intertactical heritability in preventing intralocus conflict

Abstract

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

“…Following preliminary analyses suggesting the potential for different heritability values between the sexes (see Table S1 ), we estimated sex‐specific heritabilities as twice the slope from the regression of sex‐specific mean standardized offspring length against the standardized length of each sire and dam in each population and year ( h 2 = 2 b op ; Falconer, 1989 ). This approach has been used to estimate heritability values in other wild populations, including populations of salmonids (Abadía‐Cardoso et al, 2013 ; Dickerson et al, 2005 ; Gamble & Calsbeek, 2021 ).…”

“…to estimate heritability values in other wild populations, including populations of salmonids (Abadía-Cardoso et al, 2013;Dickerson et al, 2005;Gamble & Calsbeek, 2021).…”

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

“…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%).…”