Family Dominance at the Fry Stage Weakly Influences Mean Family Body Length at Smolting in Hatchery-Reared Steelhead

<p>Steelhead <i>Oncorhynchus mykiss</i> reared in hatcheries rapidly adapt to captivity. However, the traits under selection in captivity are not well understood. Hatchery-reared salmonids are generally more aggressive than wild fish. Therefore, it is possible that selection in hatcheries favors increased aggressiveness because aggressive fish may dominate food resources and grow larger, resulting in a fitness advantage at release. We tested whether family dominance at the fry stage correlates with mean family fork length at smolting of the same families raised in a parallel experiment. Family dominance was assessed when families were first interacting with each other as fry. Juveniles in the parallel experiment were raised at high or low density to determine whether the effect of family dominance on mean family fork length was stronger at low density. More-dominant families were slightly larger at smolting, and the effect changed little between density treatments. Although the effect we observed was modest, these data are consistent with the hypothesis that dominance as fry is a trait under selection in hatcheries.</p> <p>Received April 8, 2016; accepted July 28, 2016 Published online October 7, 2016 </p

Winter_run steelhead hatchery genotypes

Genotype data from winter-run hatchery steelhead

Effect of genetic background and <i>sod1</i> genotype on life-history traits.

<p>(A) Average size by genotypic class within each lineage at 12 weeks after egg masses were deposited. The points represent the averages of the mean size of individuals of each genotype within each of 3–4 cups (containing 13–17 F2 snails per cup). Error bars represent 1±SE (background 1: n = 45 (<i>BB</i> = 16, <i>BC</i> = 20, <i>CC</i> = 9), background 2: n = 57 (<i>BB</i> = 16, <i>BC</i> = 28, <i>CC</i> = 13) background 3: n = 58 (<i>BB</i> = 16, <i>BC</i> = 28, <i>CC</i> = 14)). Snails with the <i>CC</i> genotype grew significantly more slowly than those with <i>BC</i> and <i>BB</i> genotypes. (B) Average size at 32 weeks of each genotypic class within each lineage. Means are the average of all snails within the genotypic class, and error bars represent 1±SE (background 1: n = 27 (<i>BB</i> = 9, <i>BC</i> = 10, <i>CC</i> = 8), background 2: n = 27 (<i>BB</i> = 9, <i>BC</i> = 10, <i>CC</i> = 8), background 3: n = 30 (<i>BB</i> = 10, <i>BC</i> = 10, <i>CC</i> = 10)). Again, snails with the <i>CC</i> genotype grew significantly more slowly than those with <i>BC</i> and <i>BB</i> genotypes. (C) Average total egg production for five weeks per snail (each raised individually) by genotypic class within each lineage. Means are the average of all snails within the genotypic class, and error bars represent 1±SE (background 1: n = 25 (<i>BB</i> = 9, <i>BC</i> = 9,<i>CC</i> = 7), background 2: n = 27 (<i>BB</i> = 9, <i>BC</i> = 10, <i>CC</i> = 8), background 3: n = 30 (<i>BB</i> = 10, <i>BC</i> = 10,<i>CC</i> = 10)). (D) Mortality at 8-month census of each genotypic class within each lineage. Data points are estimates of the percent mortality in each genotypic class and error bars represent 1±SE on the proportion (for all backgrounds n = 30 (<i>BB</i> = 10, <i>BC</i> = 10, <i>CC</i> = 10)). Snails with the <i>CC</i> genotype exhibited significantly greater mortality than those with the <i>BB</i> or <i>BC</i> genotype. (E) Mortality at 12-month census of each genotypic class within each lineage. Data points are estimates of percent mortality in each genotypic class and error bars represent 1±SE on the proportion (for all backgrounds n = 30 (<i>BB</i> = 10, <i>BC</i> = 10, <i>CC</i> = 10)).</p

Breeding scheme for generating F2 populations with different genetic backgrounds.

<p>We created F2 populations by crossing inbred lines (3 generations of selfing) that were fixed for <i>BB</i> or <i>CC</i> genotypes. F1 offspring from unique inbred line crosses (fixed for the <i>BC</i> genotype) were then bred to generate outbred F2 populations that were segregating for <i>BB</i>, <i>BC</i>, <i>CC</i> genotypes in the expected Mendelian ratio. This was done three times to generate three different genetic backgrounds that differ in average resistance.</p

Resistance of genetic background as a function of average resistance of grandparental inbred lines.

<p>Mid-grandparent resistance was estimated by averaging the resistance of the four inbred, grandparental lines (determined previously). The resistance of each genetic background (Grand-offspring resistance) was estimated by parasite challenges done in triplicate (n = 24×3) for each background (• genetic background 1, ▴ genetic background 2, and ▪ genetic background 3).</p

Lithobates (Rana) pipiens microsatellite data

Lithobates (Rana) pipiens microsatellite dat

Rana luteiventris microsatellite data

GENEPOP input file

Rana cascadae microsatellite data

GENEPOP input file

Rana pretiosa microsatellite data

GENEPOP input file

F_ST values between the unselected control line (GUA) and each selected line (R10 and R30).

<p>Three null RAD markers, aligned with BWA [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005067#pgen.1005067.ref065" target="_blank">65</a>] to Scaffold1, all showed unusually high F_ST in one or both comparisons (red). These markers conform to perfect linkage disequilibrium with the haplotypes as determined by Sanger sequencing, with the different F_ST values owing only to the error inherent in estimating allele frequencies from null markers. An additional unaligned marker with high F_ST in both comparisons was identified with Stacks [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005067#pgen.1005067.ref035" target="_blank">35</a>] and found to reside on Scaffold4 (blue).</p