Wennevik, V. | Search bioRxiv

bioRxiv2022

Overruled by nature: A plastic response to an ecological regime shift disconnects a gene and its trait

In Atlantic salmon, age at maturation is a life history trait ruled by a sex-specific trade-off between reproductive success and survival. Following an ecological regime shift in 2005, many North Atlantic salmon populations currently display smaller size at age and delayed age at maturation. However, whether this change reflects rapid evolution or plastic response is unknown. Some 1500 historical and contemporary salmon from river Etne (Western Norway) genotyped at 50k SNPs revealed three loci significantly associated with age at maturation. These included vgll3 and six6, which collectively explained 36 to 50% of the age at maturation variation in the 1983-1984 period. Strikingly, the combined influence of these genes was nearly absent in all samples from 2013-2016, despite allelic frequencies at vgll3 remaining unchanged. We conclude that the regime shift has led to the sudden bypassing of the influence of vgll3 and six6 on maturation through growth-driven plasticity.

genetics↗

bioRxiv2019

Life history genomic regions explain differences in Atlantic salmon marine diet specialization

O_LIAnimals employ various foraging strategies along their ontogeny to acquire energy, and with varying degree of efficiencies, to support growth, maturation and subsequent reproduction events. Individuals that can efficiently acquire energy early are more likely to mature at an earlier age, as a result of faster energy gain which can fuel maturation and reproduction. C_LIO_LIWe aimed to test the hypothesis that heritable resource acquisition variation that co-varies with efficiency along the ontogeny would influence maturation timing of individuals. C_LIO_LITo test this hypothesis, we utilized Atlantic salmon as a model which exhibit a simple, hence trackable, genetic control of maturation age. We then monitored the variation in diet acquisition (quantified as the stomach fullness and composition) of individuals with different ages, and linked it genomic regions (haploblocks) that were previously identified to be associated with age-at-maturity. C_LIO_LIConsistent with the hypothesis, we demonstrated that one of the life history genomic regions tested (six6) was indeed associated with age-dependent differences in stomach fullness. Prey composition was marginally linked to both genomic regions (six6 and vgll3). We further showed Atlantic salmon switched to the so-called "feast and famine" strategy along the ontogeny, where older age groups exhibited heavier stomach content, but that came at the expense of running on empty more often. C_LIO_LIThese results suggest genetic variation underlying resource utilization variation may explain the genetic basis of age structure in Atlantic salmon. Given that ontogenetic diet has a genetic component and the strong spatial diversity associated with these genomic regions, we predict populations with diverse maturation age will have diverse evolutionary responses to future changes in marine food-web structures. C_LI

ecology↗