MS (Sophie) Valk, MSc

I feel very passionate about marine organisms and the ecosystems they inhabit. Although I am still at an early stage of my scientific career, I have developed a strong interest in molecular ecology. My research interests lie at applying molecular approaches to understand marine ecology. Outside of research, I enjoy sports and spending time in nature.

Academic path

I obtained my Bsc in Biology from Wageningen University in 2019, followed by an Msc in Aquaculture and Marine Resource Management in 2021. In 2022, I started my PhD with the Marine Animal Ecology group.

Current work

My PhD research focuses on the genetic and epigenetic diversity of the European flat oyster (Ostrea edulis). Once widespread in the North Sea, flat oyster populations have declined drastically due to disease, habitat loss, and overfishing, leading to local functional extinction in some areas. Because oyster reefs provide essential habitat for many marine species, restoring flat oyster populations is important for sustaining North Sea biodiversity.

Current restoration efforts involve translocating oysters from other regions or introducing hatchery-produced native oysters. However, the effects of these practices on the genetic diversity of wild populations are still poorly understood. Maintaining genetic diversity is essential for long-term, sustainable restoration. My research therefore aims to characterize geneticdiversity in flat oyster populations in the Netherlands and to assess genetic divergence between wild populations and oysters used in restoration projects.

A key challenge in oyster restoration is their unusual reproductive biology. Flat oysters show highly variable reproductive success and can reverse sex. As they do not display clear sexual dimorphism and lack identified sex chromosomes, determining sex currently requires lethal sampling. As a result, sex ratios in both wild and cultured populations are often unknown, even though skewed sex ratios can negatively affect genetic diversity.

Recent research suggests that epigenetic mechanisms, particularly DNA methylation, play an important role in sex reversal in oysters. In my work, I investigate sex-specific DNA methylation patterns with the aim of developing non-lethal methods for sex identification. We found that hermaphrodite oysters show distinct DNA methylation patterns in gill tissue, where differential methylation is enriched in genes mainly linked to energy metabolism, suggesting changes in energy balance during sex reversal. These findings open the door to using epigenetic biomarkers for non-lethal sex identification in future restoration efforts. Find the full publication here if you want to read more: https://pubmed.ncbi.nlm.nih.gov/40481401/

By elucidating (epi)genetic diversity I aim to contribute to support long-term sustainable restoration of the European flat oyster.

Methods

• SNP characterization
• Structural variant detection
• Nanopore sequencing
• DNA methylation analysis