Genotype-specific variation in seasonal body condition at a large-effect maturation locus

Organisms utilize varying lipid resource allocation strategies as a means to survive seasonal environmental changes and life-history stage transitions. In Atlantic salmon, a certain lipid threshold is needed to initiate sexual maturation. Because of this, an individual’s maturation schedule may be affected by changes in temperature and food availability across the seasons that create natural fluctuations of lipid reserves.Recent studies have found a genome region, including the genevgll3,that explains a large proportion of variation for size and age at maturity. Vgll3encodes a transcription co-factor that acts as an inhibitor of adipogenesis in mice and also affects condition factor and other phenotypes in juvenile salmon. However, even with many studies investigating varying temperature effects, there is a lack of temporal studies examining the effects of seasonality on such phenotypes, nor have the effects ofvgll3genotype on condition factor and maturation in different temperatures at different life stages.Here, we investigate the influence of different larval and juvenile incubation temperatures,vgll3genotype and their interactions on juvenile salmon phenotypes including body condition, and sexual maturation rate. We reared Atlantic salmon for 2 years in varying temperatures with an average 1.76 °C difference between warm and cold treatments in four different larval-juvenile phase treatment groups (Warm-Warm, Warm-Cold, Cold-Warm, and Cold-Cold) until the first occurrence of maturation in males.We found no effect of larval temperature on the measured phenotypes or maturation rate, suggesting the occurrence of growth compensation over the course of the experiment. Agreeing with previous studies, an increased maturation rate was observed in individuals of the warm juvenile temperature treatment.In addition, we observed differences in condition factor associated withvgll3genotype, wherebyvgll3*EEindividuals (the genotype associated with early maturation) had a less variable condition factor across the seasons compared to thevgll3*LL(associated with late maturation) individuals.This result suggests avgll3influence on resource acquisition and allocation strategies, possibly linked with the early maturation process, with individuals carrying the early maturationvgll3genotype having a higher early maturation rate and a higher condition factor in the spring.