Exploring epigenetic patterns of spawning time in larval Clupea harengus (Atlantic herring) exposed to temperature and photoperiodicity stress

Background/Question/Methods

Research on Atlantic herring (Clupea harengus), a coastal pelagic fish of economic and ecological significance, have largely contributed to our knowledge on population structure of oceanic pelagic fish. Studies on seasonal spawning time as well as larval dispersal and retention have contributed to our understanding of the complex metapopulation structure of this system, but few have investigated the genetic mechanisms of the early stages of development in this system particularly at the gene expression level. Previous studies have described genes affecting spawning time as a function of temperature and photoperiodicity, but little is known about the effects of these environmental factors on the gene expression at early developmental stages. Here we examine methylation patterns of larval herring under different environmental regimes to better understand how environmental stressors affect spawning time at the epigenetic level. A reciprocal transplant experiment using two temperatures (11°C and 13°C) and two light treatments (6h and 12h) was set up and samples for whole genome bisulfite sequencing were taken at three stages of development prior to first feeding (pre-hatch, post-hatch, and yolk absorption stages).

Results/Conclusions

While no effects were detected on genome wide methylation patterns from photoperiodicity or temperature, larvae derived from late spawning herring reveal consistently high levels of global methylation across all samples (average 74.07%). Importantly, a decrease in global methylation levels was detected across the three stages of development, with an increase in hypermethylation at differentially methylated regions in concordance with literature. Overall, changes in gene expression appears to differentiate the stages of larval development. Consequently, future studies can work to resolve which environmental variables are contributing towards the changes in gene expression.