External Seminar: Christian BRAENDLE

Gianni LITI invites: Christian BRAENDLE – Institut de Biologie Valrose

« Neural circuit evolution and the transition to viviparity in Caenorhabditis nematodes »

 Abstract: The behavioural and genetic mechanisms driving transitions from oviparity to viviparity remain poorly understood, and Caenorhabditis nematodes, which share a simple, well-characterised egg-laying circuit but vary widely in reproductive behaviour, offer a powerful system to address this question. Within C. elegans, natural populations differ markedly in egg-laying behaviour and serotonin sensitivity, and the QTL and molecular variants we are identifying act on environmental sensitivity, vulval muscle excitability, and neuromodulatory signalling, showing that single natural mutations can substantially alter a fundamental reproductive trait. Across more than 40 Caenorhabditis species, we find extensive variation in egg retention and neuromodulatory responses, including multiple independent shifts toward elevated egg retention and the emergence of obligate viviparity in one species. Despite broad conservation of the egg-laying system, this transition involves extensive changes in neuromodulation, muscle excitability, and vulval morphology, including a switch from serotonergic to cholinergic control of offspring release. By combining quantitative genetics within C. elegans with comparative analyses across the genus, this work links microevolutionary and macroevolutionary change and shows how neural circuit evolution can drive major shifts in reproductive strategy.