Courtship plasticity reveals the evolution of dialects in allopatric fish populations

Traditionally, reproductive isolation between disjoint populations has been thought to emerge as a result of the accumulation of different mutations, genetic drift, or through the effects of natural and sexual selection^1^. Alternatively, the ability of an organism to express different phenotypes depending on the environment (i.e. phenotypic plasticity) could produce reproductive isolation^2,3^. Sexually selected traits are expected to be phenotypically plastic and can result in modifications of the species recognition system and thus originate new species^4^. Here we show that the population-characteristic male courtship behaviour of a fish (Girardinichthys multiradiatus) is modified in the presence of females from other populations, that this is due to the males responding to subtle cues from females, and that they fail to emulate the female's population-characteristic behaviour. We conclude that plasticity has led to the creation of local dialects in the courtship pattern that hampers communication between heterogametic individuals and promotes pre-mating isolation