Testicular heterochrony in vgll3-mediated maturation age in Atlantic salmon.

Heterochrony, or shifts in developmental timing, drives phenotypic diversity within and between species and shapes life history traits that can be selected for in changing environments, which in turn promotes population resilience. Mutations in heterochronic genes that regulate these processes can induce stable timing shifts, impacting important life history traits such as pubertal timing. Age at maturity is a key adaptive trait across species, with vestigial-like family member 3 (vgll3), a Hippo pathway cofactor, as a main determinant in Atlantic salmon. Recent studies show that early (E) and late (L) vgll3 alleles affect reproductive gene expression in salmon, reinforcing its role in regulating developmental timing. This study examines whether vgll3 influences testicular heterochrony in Atlantic salmon by analyzing gene expression related to the Hippo pathway. We observed heterochronic divergence in Hippo pathway gene transcription, indicating accelerated changes linked to spermatogenesis in vgll3*EE individuals. Our results position vgll3 as a heterochronic gene with a key role in regulating developmental timing in salmon.