Causes and consequences of recent freshwater invasions by saltwater animals

Transitions from marine to freshwater habitats constitute dramatic shifts between ‘adaptive zones’ that have initiated the radiation and speciation of many taxa. As recently as 10 000 years ago, deglaciation resulted in marine fauna being trapped in freshwater lakes. In modern times, human activity has caused the acceleration of freshwater invasions from marine or brackish habitats, leading to serious environmental problems. The rapid pace of these invasions provides ideal opportunities for examining initial responses to environmental change and mechanisms involved in habitat transitions. Despite conservation implications and evolutionary applications, recent transitions to fresh water remain inadequately explored.