Speciation in Mnemiopsis

Understanding how populations diverge is one of the oldest and most compelling questions in evolutionary biology but our grasp on the genomic mechanisms underpinning divergence is limited to a handful of species. Indeed, we know even less about divergence in the open ocean, where barriers to gene flow are seemingly absent. Here, we present the most comprehensive genomic study, to date, of the highly invasive, holopelagic invertebrate, Mnemiopsis. We resolve the long-standing taxonomic uncertainty of Mnemiopsis, identifying two distinct species whose divergence coincides with historical glacial melting. We define a hybrid zone, highlight substantial structural variation between species, and uncover key genes linked to environmental adaptation and invasive success. These findings connect microevolutionary processes with macroevolutionary patterns and provide new insights into how ocean dynamics drive speciation and adaptation in pelagic ecosystems.