Internship Proposal - Master 2

Title

Impacts of harbour development on the larval recruitment and metamorphosis of the common two-banded sea bream Diplodus vulgaris

Laboratory

UMR 7232 CNRS-SU, Biologie Intégrative des Organismes Marins (BIOM), Team EcoEvoDevo

Address

Observatoire Océanologie de Banyuls-sur-Mer, 1 avenue Pierre Fabre, Banyuls-sur-Mer, France

Dates

January to July 2025

Stipend

Yes (~600€/month in France)

Summary

Most marine fishes have a bipartite life cycle, with a pelagic and dispersing larval phase followed by more sedentary juvenile and adult phases within coastal habitats. Research from our group showed that, in coral reef fishes, the transition from the larval to the juvenile phase, called larval recruitment, coincides with a metamorphosis controlled by thyroid hormones (TH). We also showed that it is also the case for temperate reef fishes like the common two-banded sea bream Diplodus vulgaris, although a better characterization of this transition is still needed.

Under the control of TH and metamorphic genes from the TH pathway, larval fishes undergo rapid and major morphological, physiological, and behavioural changes during metamorphosis. These changes are critical for fish survival in the juvenile populations within coastal habitats. Our previous research on coral-reef fishes showed that TH endocrine disruption induced by anthropogenic stressors such as increased temperatures and pollutants can lead to altered metamorphic changes, ultimately impairing juvenile fish survival and threatening the replenishment of fish populations. It is therefore possible to examine the ‘quality’ of larval and juvenile fish in their nursery habitats by looking at their TH levels, levels of expression of metamorphic genes, and metamorphic traits such as size, shape, body condition, pigmentation patterns, and specific behaviours. By coupling these biomarkers with environmental parameters measured in nursery habitats (such as levels of certain pollution like heavy metals, pesticide, temperature, turbidity, and nutrient levels), it is thus possible to distinguish nurseries that are healthy habitats for metamorphosing fishes from nurseries that are ecological traps.

In this context, the intern will participate to the JUVAPORT project, which aims at investigating the effects of the construction of a new wharf in the harbour of Port-Vendres onto the ecological quality of the surrounding fish nurseries. To do so, we have sampled metamorphosing D. vulgaris from four different nursery zones of the harbour, including the new wharf area, since 2021 (i.e. three years before the beginning of the wharf construction) and will pursue this sampling again this year (second and last year of the wharf construction). The intern will thus participate in sampling larval and juvenile D. vulgaris to evaluate their ecophysiology and metamorphic proceedings in the nursery habitats of the Port-Vendres harbour in response to the new wharf construction. In particular, the intern will (i) perform molecular biology analyses (hormonal extractions for triiodothyronine T3, thyroxine T4, cortisol; RNA extraction and qPCR on TRα, TRβ, Klf9 genes) to evaluate the dynamics of the TH signalling pathway in D. vulgaris early life stages ; (ii) examine pigmentation pattern (e.g., appearance of the tail peduncle black bar), morphological traits (e.g., standard length, body height, eye diameter) and body condition (weight / length ratio). To do so, the intern will use stereomicroscopy and computer vision techniques. The intern will take advantage of a 5-year time series (3 years before and 2 years during the wharf construction) to evaluate how these traits, which determine the ecophysiological “quality” of juvenile fish and, in turn, the ecological quality of their nursery habitat, have potentially been impacted by the wharf construction.

The intern will thus (i) gain knowledge in fish ecophysiology and neuroendocrinology, sampling, and histology; (ii) develop biomolecular and laboratory techniques for measuring hormonal levels, gene expression levels, and pigmentation patterns; (iii) practice bioinformatic techniques for analyzing and visualizing data; and (iv) acquire communication skills to present and share scientific results.

References

  • Roux N., Miura S., Dussene M., Tara Y., Lee S.-H., de Bernard S., Reynaud M., Salis P., Barua A., Boulathouf A., Balaguer P., Gauthier K., Lecchini D., Gibert Y., Besseau L., Laudet V. 2023. The multi-level regulation of clownfish metamorphosis by thyroid hormones. Cell Reports.
  • Gairin, E., Dussenne, M., Mercader, M., Berthe, C., Reynaud, M., Metian, M., Mills, S.C., Lenfant, P., Besseau, L., Bertucci, F. Lecchini, D. 2022. Harbours as unique environmental sites of multiple anthropogenic stresses on fish hormonal systems. Molecular & Cellular Endocrinology.
  • Besson M., Feeney W.E., Moniz I., François L., Brooker R.M., Holzer G., Metian M., Roux N., Laudet V., Lecchini D. 2020. Anthropogenic stressors impact fish sensory development and survival via thyroid disruption. Nature Communications.
  • Holzer G., Besson M., Lambert A., François L., Barth P., Gillet B., Hughes S., Piganeau G., Leulier F., Viriot L., Lecchini D., Laudet V. 2017. Fish larval recruitment to reefs is a thyroid hormone-mediated metamorphosis sensitive to the pesticide chlorpyrifos. eLife.

Apply

Contact both supervisors with a CV, a Cover Letter, and references if relevant. Position opened until filled.