The influence of vgll3 genotypes on sea age at maturity is altered in farmed mowi strain Atlantic salmon

Abstract

Background: In Atlantic salmon in the wild, age at maturity is strongly influenced by the vgll3 locus. Under farming conditions, light, temperature and feeding regimes are known significantly advance or delay age at maturity. However, the potential influence of the vgll3 locus on the maturation of salmon reared under farming conditions has been rarely investigated, especially in females.

Results: Here, we reared domesticated salmon (mowi strain) with different vgll3 genotypes under standard farming conditions until they matured at either one, two or more than two sea winters. Interestingly, and in contrast to previous findings in the wild, we were not able to identify a link between vgll3 and age at maturity in females when reared under farming conditions. For males however, we found that the probability of delaying maturation from one to two sea winters was significantly lower in fish homozygous for the early allele compared to homozygous fish for the late allele, while the probability for heterozygous fish was intermediate. These data also contrast to previous findings in the wild where the early allele has been reported as dominant. However, we found that the probability of males delaying maturation from two to three sea winters was regulated in the same manner as the wild.

Conclusions: Collectively, our data suggest that increased growth rates in mowi salmon, caused by high feed intake and artificial light and temperature regimes together with other possible genetic/epigenetic components, may significantly influence the impact that the vgll3 locus has on age at maturity, especially in females. In turn, our results show that the vgll3 locus can only to a large extent be used in selective breeding to control age at maturation in mowi males. In summary, we here show that in contrast to the situation in wild salmon, under farming conditions vgll3 does not seem to influence age at maturity in mowi females whereas in mowi males, maturing as one or two sea winters it alters the early allele effect from dominant to intermediate.

Keywords: Age at puberty; Aquaculture; Atlantic salmon; Genotype phenotype interaction; GxE; Reproduction; Sex dependent penetrance; Time at maturity; Vestigial like protein 3; vgll3.

Fig. 1

Genotype phenotype interaction in females. Graphs a-b show phenotype frequencies (1, 2 or > 2SW) per genotype (EE, EL, LL) and family in females (mowi strain) reared from two different year-classes (Y1 and Y2, fig a and b respectively). Graph c show the probability of delaying maturation (>2SW, instead of 2SW) when comparing Y1 and Y2 females. Maturation phenotypes are denoted 1SW, 2SW and > 2SW and correspond to fish maturing after 1, 2 or > 2 sea winters (SW). Genotypes are denoted as EE (Early-Early), EL (Early-Late) and LL (Late-Late). Graphs a-b shows SEM. Graph c shows confidence interval for the probability for delaying maturation, different lower-case letters indicate significant differences (P < 0.05)

Fig. 2

Genotype phenotype interaction in males. Graphs a and b show maturity frequencies in males (mowi strain, 1, 2 or > 2SW) in relation to sea age genotypes (EE, EL and LL) and family in fish from two different year-classes (Y1 and Y2, a and b, respectively). Graph c show the probability of delaying maturation when comparing genotypes (EE, EL and LL) and year-class (Y1 and Y2). Maturation phenotypes are denoted 1SW, 2SW and > 2SW and correspond to fish maturing after 1, 2 or > 2SW sea winters (SW). Genotypes are denoted as EE (Early-Early), EL (Early-Late) and LL (Late-Late). Graphs a-b show SEM. Graph c shows confidence interval for the probability for delaying maturation, different lower-case letters indicate significant differences (P < 0.05)