Dear MARMAM community, On behalf of the organizing team of the workshop *“Losing genes: deciphering the mechanisms behind gene loss in cetaceans”* at ECS 2026, we warmly invite you to participate in our workshop, which will take place on Monday, April 20, as a half-day event. Please find below detailed information about the workshop, as well as the registration link. Should you have any questions, please do not hesitate to contact us. Gene loss is a key molecular evolutionary mechanism driving adaptation to novel ecological niches. This process does not necessarily entail complete gene deletion but can also arise from mutations that disrupt protein function or impair mRNA production. Cetaceans provide a compelling model for studying this process, due to the extensive suite of inactivation events associated with their transition from terrestrial to aquatic environments. Prior research has documented the loss or inactivation of multiple genes linked to hair follicle development, sebaceous glands, and lung function, aligning with cetaceans specific morphological and physiological traits. This workshop will be divided into two components: a theoretical section providing an overview of gene loss as an evolutionary mechanism, and a practical section in which participants will learn how to investigate gene loss using genomic resources. The practical component will introduce the use of databases such as NCBI, Gene Loss Database and Ensembl as well as tools such asPseudoChecker and Geneious Prime, providing participants with the skills to detect, annotate, and interpret gene loss events in an evolutionary framework. Registration link: https://www.europeancetaceansociety.eu/conference-workshops-37 Looking forward to see you in the conference! Raul Valente (on behalf of the Organizing team) -- *Raul Valente* PosDoc Researcher Coastal Biodiversity Lab - Interdisciplinary Centre of Marine and Environmental Research Department of Biology - Faculty of Sciences of the University of Porto *CIIMAR | Interdisciplinary Centre of Marine and Environmental Research* *of the University of Porto* Terminal de Cruzeiros do Porto de Leixões Avenida General Norton de Matos, S/N 4450-208 Matosinhos | Portugal E-mail: *raulfonsecavalente@gmail.com <raulfonsecavalente@gmail.com>*