Abstract
Phenotypic plasticity is an important driver of species resilience.
Often mediated by epigenetic changes, phenotypic plasticity enables
individual genotypes to express variable phenotypes in response to
environmental change. Barramundi (Lates calcarifer) is a protandrous
(male-first) sequential hermaphrodite that exhibit plasticity in
length-at-sex change between geographic regions. This plasticity is
likely to be mediated by changes in DNA methylation (DNAm), a
well-studied epigenetic modification. However, region-specific
relationships between length, sex and DNAm in sequential hermaphrodites
were previously unreported. To investigate these relationships, here we
compare DNAm in four conserved vertebrate sex-determining genes in male
and female barramundi of differing lengths from three regions of
northern Australia. Despite a strong association between increasing
length and male-to-female sex change, the data reveal that DNAm becomes
more sex-specific (rather than more female-specific) with length.
Significant differences in DNAm between males and females of similar
lengths suggest that female-specific DNAm arises rapidly during sex
change, rather than gradually with growth. The findings also reveal that
region-specific differences in length-at-sex change are accompanied by
differences in DNAm, and were concurrent with variability in remotely
sensed sea temperature and salinity. Together, these findings provide
the first in situ evidence for epigenetically and environmentally
mediated sex change in a protandrous hermaphrodite, and offer
significant insight into the molecular and ecological processes
governing the marked and unique plasticity of sex in fish.